相關申請
此為2016年8月2日提交之美國專利申請第15/226,546號之部分接續申請，該案主張2015年9月25日提交之美國臨時申請第62/232,796號之優先權。彼等申請之全部內容以引用的方式併入本文中。 用於形成太陽能電池電極之導電膠通常包括導電金屬粒子、一或多種玻璃料、有機載體及視情況選用之一或多種添加劑。本發明之有機載體係用於形成導電膠組合物以用於具有改進電學性質之PERC之太陽能電池上的背側焊接片。有機載體
本發明之有機載體提供介質，藉由該介質可將導電金屬粒子及玻璃料施加至矽表面以形成背側焊接片。較佳有機載體為由一或多種較佳為有機溶劑之溶劑形成之溶液、乳液或分散液，該等溶劑確保膠之組分呈溶解、乳化或分散態存在。較佳為提供導電性組合物之組分之最佳穩定性且改進所得PERC之太陽能電池之電氣效能的有機載體。 在一個實施例中，以導電膠組合物之100%總重量計，有機載體以至少約5 wt%、較佳至少約10 wt%、更佳至少約15 wt%、更佳至少約20 wt%且最佳至少25 wt%之量存在於導電性組合物中。同時，以導電膠組合物之100%總重量計，有機載體較佳不超過約60 wt%、較佳不超過約55 wt%且更佳不超過約50 wt%。 在較佳實施例中，有機載體包含至少一種聚矽氧烷化合物。聚矽氧烷化合物為具有多個具有Si-O-Si鍵之矽氧烷官能基之化合物。在較佳實施例中，聚矽氧烷化合物為聚矽氧油，其為具有有機側鏈之液體聚合的矽氧烷。聚矽氧烷化合物在導電膠組合物中之用途顯示為最小化對PERC之太陽能電池之背表面層的蝕刻，由此改進PERC之太陽能電池之開路電壓(Voc)及效率(Eta)。可使用任何適合用於導電膠組合物之聚矽氧油。在較佳實施例中，使用黏度為約1-40 kcps之聚矽氧油，較佳使用黏度為約1-10 kcps，諸如約5 kcP之聚矽氧油，或黏度為約25-35 kcps，諸如約30 kcps之聚矽氧油。根據本文所闡述之方法量測黏度。 在一個實施例中，以有機載體之100%總重量計，有機載體包含至少約0.5 wt%聚矽氧油。同時，有機載體包含不超過約20 wt%聚矽氧油、較佳不超過約15 wt%且最佳不超過約13 wt%。 關於作為整體之膠組合物，以導電膠之100%總重量計，聚矽氧油較佳以至少0.1 wt%且較佳至少約0.2 wt%、更佳至少0.5 wt%且最佳至少1 wt%之量存在。同時，以導電膠之100%總重量計，聚矽氧油較佳以不超過約10 wt%、較佳不超過約5 wt%之量存在。在較佳實施例中，以導電膠之100%總重量計，聚矽氧油較佳以不超過約4 wt%之量存在。在另一較佳實施例中，膠組合物包括約0.2至約3.5wt%、較佳約1至約3 wt%聚矽氧油。 在一個實施例中，一或多種聚矽氧烷化合物分別自有機載體或任何其他膠組分併入導電膠中。一或多種聚矽氧烷化合物可與其他膠組分，亦即導電金屬粒子、玻璃料及有機載體一起添加，或可在已組合膠組分後將一或多種聚矽氧烷化合物添加至膠組合物中。在較佳實施例中，一或多種聚矽氧烷化合物在與剩餘的有機載體組分組合之前與至少一種溶劑混合在一起。在一個實施例中，在組合時觀察溶劑與聚矽氧烷之交互作用以便測定其是否其充分混合或分離。 在一個實施例中，有機載體進一步包括至少一種有機溶劑及至少一種樹脂(例如聚合物)。在較佳實施例中，有機載體包含至少一種有機溶劑、至少一種樹脂、至少一種聚矽氧烷化合物或其任何組合。 較佳樹脂為彼等有助於形成具有有利可印刷性及黏度之導電性組合物的樹脂。此項技術中已知且視為適合於本發明之上下文的所有樹脂均可用作有機載體中之樹脂。較佳樹脂包括但不限於聚合樹脂、單體樹脂及為聚合物與單體之組合的樹脂。聚合樹脂亦可為其中在單個分子中含有至少兩種不同單體單元之共聚物。較佳聚合樹脂為彼等在聚合物主鏈中攜帶官能基之樹脂、彼等在主鏈外攜帶官能基之樹脂及彼等在主鏈內與主鏈外均攜帶官能基之樹脂。較佳在主鏈中攜帶官能基之聚合物包括例如聚酯、經取代之聚酯、聚碳酸酯、經取代之聚碳酸酯、在主鏈中攜帶環基之聚合物、聚糖、經取代之聚糖、聚胺基甲酸酯、經取代之聚胺基甲酸酯、聚醯胺、經取代之聚醯胺、酚類樹脂、經取代之酚類樹脂、前述聚合物中一或多者之單體視情況與其他共聚單體之共聚物或其至少兩者之組合。根據一個實施例，樹脂可為聚乙烯醇縮丁醛或聚乙烯。較佳在主鏈中攜帶環基之聚合物包括例如聚丁酸乙烯酯(polyvinylbutylate，PVB)及其衍生物，及聚萜品醇及其衍生物，或其混合物。較佳聚糖包括例如纖維素及其烷基衍生物，較佳為甲基纖維素、乙基纖維素、羥乙基纖維素、丙基纖維素、羥丙基纖維素、丁基纖維素及其衍生物及其至少兩者之混合物。其他較佳聚合物包括例如纖維素酯樹脂，例如乙酸丙酸纖維素、乙酸丁酸纖維素及其任何組合。較佳在主要聚合物鏈外攜帶官能基之聚合物包括彼等攜帶醯胺基之聚合物、常稱為丙烯酸樹脂之彼等攜帶酸及/或酯基之聚合物或攜帶前述官能基之組合之聚合物或其組合。較佳在主鏈外攜帶醯胺之聚合物包括例如聚乙烯吡咯啶酮(PVP)及其衍生物。較佳在主鏈外攜帶酸及/或酯基之聚合物包括例如聚丙烯酸及其衍生物、聚甲基丙烯酸酯(PMA)及其衍生物或聚甲基丙烯酸甲酯(PMMA)及其衍生物或其混合物。較佳單體樹脂為基於乙二醇之單體、萜品醇樹脂或松脂衍生物或其混合物。較佳基於乙二醇之單體樹脂為彼等具有多個醚基、多個酯基之樹脂或彼等具有一個醚基及一個酯基之樹脂，較佳醚基為甲基、乙基、丙基、丁基、戊基、己基及高碳烷基醚，較佳酯基為乙酸酯及其烷基衍生物，較佳乙二醇單丁醚單乙酸酯，或其混合物。松酯膠樹脂、聚丁酸乙烯酯及乙基纖維素為最佳樹脂。在一個實施例中，乙基纖維素用作黏合劑。 以有機載體之100%總重量計，樹脂可以至少約0.5 wt%、較佳至少約1 wt%且最佳至少約3 wt%之量存在。同時，以有機載體之100%總重量計，樹脂可以不超過約10 wt%且較佳不超過約8 wt%之量存在。在一個實施例中，以有機載體之100%總重量計，樹脂以約5 wt%量存在。 較佳溶劑為在燃燒期間以顯著程度自膠移除之組分。較佳地，其在燃燒之後呈現的絕對重量與在燃燒之前相比較降低至少約80%，較佳與在燃燒之前相比較降低至少約95%。較佳溶劑為彼等有助於有利黏度及可印刷性特徵之溶劑。此項技術中已知且視為適合於本發明之上下文的所有溶劑均可用作有機載體中之溶劑。較佳溶劑為彼等在標準環境溫度及壓力(SATP) (298.15 K，25℃，77℉)、100 kPa (14.504 psi，0.986 atm)下以液體形式存在之溶劑，較佳為彼等沸點高於約90℃且熔點高於約-20℃之溶劑。較佳溶劑為極性的或非極性的，質子的或非質子的，芳族或非芳族的。較佳溶劑包括例如單醇、二醇、聚醇、單酯、二酯、聚酯、單醚、二醚、聚醚、包含此等類別官能基之至少一或多者且視情況包含其他類別官能基(較佳環基、芳族基、不飽和鍵、一或多個O原子經雜原子替換之醇基、一或多個O原子經雜原子替換之醚基、一或多個O原子經雜原子替換之酯基)之溶劑及前述溶劑之兩者或超過兩者之混合物。此上下文中之較佳酯包括例如己二酸之二烷基酯，較佳烷基成分為甲基、乙基、丙基、丁基、戊基、己基及高碳烷基或兩個不同該等烷基之組合，較佳為己二酸二甲酯及兩種或超過兩種己二酸酯之混合物。此上下文中之較佳醚包括例如二醚，較佳乙二醇之二烷基醚，較佳烷基成分為甲基、乙基、丙基、丁基、戊基、己基及高碳烷基或兩種不同該等烷基之組合及兩種二醚之混合物。此上下文中之較佳醇包括例如一級、二級及三級醇，較佳三級醇，較佳萜品醇及其衍生物，或兩種或超過兩種醇之混合物。組合超過一種不同官能基之較佳溶劑為2,2,4-三甲基-1,3-戊二醇單異丁酸酯(常稱為texanol)及其衍生物；2-(2-乙氧基乙氧基)乙醇(常稱為卡必醇)，其烷基衍生物，較佳甲基、乙基、丙基、丁基、戊基及己基卡必醇，較佳己基卡必醇或丁基卡必醇，及其乙酸酯衍生物，較佳丁基卡必醇乙酸酯；或前述至少兩者之混合物。在較佳實施例中，溶劑包括丁基卡必醇、丁基卡必醇乙酸酯、萜品醇中之至少一者或其混合物。咸信此等三種溶劑與聚矽氧烷化合物充分混合。 以有機載體之100%總重量計，有機溶劑可以至少約50 wt%且更佳至少約60 wt%且更佳至少約70 wt%之量存在。同時，以有機載體之100%總重量計，有機溶劑可以不超過約95 wt%且更佳不超過約90 wt%之量存在。 此項技術中已知之表面活性劑可與一或多種聚矽氧烷化合物一起使用。合適的表面活性劑為彼等有助於形成具有有利可印刷性及黏度特徵之導電組合物的表面活性劑。此項技術中已知且視為適合於本發明之上下文的所有表面活性劑皆可用作有機載體中之表面活性劑。較佳表面活性劑為彼等基於直鏈、支鏈、芳族鏈、氟化鏈、聚醚鏈及其組合之表面活性劑。較佳表面活性劑包括但不限於單鏈、雙鏈或多鏈聚合物。較佳表面活性劑可具有非離子、陰離子、陽離子、兩親媒性或兩性離子頭部。較佳表面活性劑可為聚合表面活性劑及單體表面活性劑或其混合物。較佳表面活性劑可具有顏料親和基，較佳具有顏料親和基之羥基官能的羧酸酯(例如DISPERBYK®-108，由BYK USA, Inc.製造)、具有顏料親和基之丙烯酸酯共聚物(例如DISPERBYK®-116，由BYK USA, Inc.製造)、具有顏料親和基之改質聚醚(例如TEGO® DISPERS 655，由Evonik Tego Chemie GmbH製造)及其他具有高顏料親和基團之表面活性劑(例如Duomeen TDO®，由Akzo Nobel N.V.製造)。不在以上清單中之其他較佳聚合物包括但不限於聚氧化乙烯、聚乙二醇及其衍生物及烷基羧酸及其衍生物或鹽，或其混合物。較佳聚乙二醇衍生物為聚(乙二醇)乙酸。較佳烷基羧酸為彼等具有完全飽和烷基鏈之烷基羧酸及彼等具有單不飽和或多不飽和烷基鏈之烷基羧酸，或其混合物。較佳具有飽和烷基鏈之羧酸為彼等烷基鏈長度在約8至約20個碳原子範圍內之羧酸，較佳為C9
H19
COOH (癸酸)、C11
H23
COOH (月桂酸)、C13
H27
COOH (肉豆蔻酸)、C15
H31
COOH (棕櫚酸)、C17
H35
COOH (硬脂酸)或鹽或其混合物。較佳具有不飽和烷基鏈之羧酸為C18
H34
O2
(油酸)及C18
H32
O2
(亞麻油酸)。 若存在，則以有機載體之100%總重量計，一或多種額外的表面活性劑可為至少約0.5 wt%。同時，以有機載體之100%總重量計，表面活性劑較佳不超過約10 wt%且較佳不超過約8 wt%。 有機載體亦可包含一或多種觸變劑及/或其他添加劑。一般熟習此項技術者已知之任何觸變劑可與本發明之有機載體一起使用。舉例而言(非限制性地)，觸變劑可衍生自天然來源或其可經合成。較佳觸變劑包括但不限於蓖麻油及其衍生物、無機黏土、聚醯胺及其衍生物、煙霧狀二氧化矽、羧酸衍生物，較佳脂肪酸衍生物(例如C9
H19
COOH (癸酸)、C11
H23
COOH (月桂酸)、C13
H27
COOH (肉豆蔻酸)、C15
H31
COOH (棕櫚酸)、C17
H35
COOH (硬脂酸)、C18
H34
O2
(油酸)、C18
H32
O2
(亞麻油酸))或其組合。亦可使用市售觸變劑，諸如(例如)Thixotrol®
MAX、Thixotrol®
ST或THIXCIN®
E。 根據一個實施例，以有機載體之100%總重量計，有機載體包含至少約1 wt%且較佳至少約7 wt%觸變劑。同時，以有機載體之100%總重量計，有機載體較佳包括不超過約20 wt%、較佳不超過約15 wt%觸變劑。 較佳有機載體中之添加劑為不同於前述組分且有助於導電性組合物之諸如改進的電氣效能及穩定性特徵之有利性質的彼等物質。可使用此項技術中已知且據認為適合於本發明之上下文的添加劑。較佳添加劑包括但不限於黏度調節劑、穩定劑、無機添加劑、增稠劑、乳化劑、分散劑及pH調節劑。若存在，則以有機載體之100%總重量計，該等添加劑較佳不超過約15 wt%。調配有機載體會影響導電膠組合物之黏度，反過來又影響其可印刷性。若黏度過高，則膠不能很好地轉移通過篩目且可能出現線斷裂或較低點。若黏度過低，則膠可能過於流體而導致印刷線擴展且縱橫比降低。如本文所闡述，為量測膠組分中之任一者之黏度，使用配備有CP-44Y樣品杯及#51圓錐體之布洛克菲爾德HBDV-III數位流變儀(Brookfield HBDV-III Digital Rheometer)。使用TC-502循環溫度浴將樣品溫度保持在25℃。設定量測間隙為0.026 mm且樣品體積為約0.5 ml。使樣品平衡兩分鐘，且接著應用1.0 rpm恆定旋轉速度一分鐘。以kcps為單位報導此間隔後之樣品黏度。導電金屬粒子
導電性組合物亦包含導電金屬粒子。較佳導電金屬粒子為彼等展現最佳導電性且在燃燒之後有效燒結以便其產生具有高導電性之電極之導電金屬粒子。此項技術中已知適用於形成太陽能電池電極之導電金屬粒子為較佳的。較佳金屬粒子包括但不限於元素金屬、合金、金屬衍生物、至少兩種金屬之混合物、至少兩種合金之混合物或至少一種金屬與至少一種合金之混合物。 在本發明之實施例中，以膠之100%總重量計，導電膠可包含至少約30 wt%、較佳至少約35 wt%、更佳至少約40 wt%、更佳至少約45 wt%且最佳至少約50 wt%金屬粒子。在較佳實施例中，以膠之100%總重量計，導電膠包含至少約60 wt%金屬粒子。同時，以膠組合物之100%總重量計，導電膠較佳包括不超過約99 wt%、較佳不超過約95 wt%、更佳不超過約90 wt%、更佳不超過約85 wt%、更佳不超過約80 wt%、更佳不超過約75 wt%、更佳不超過約70 wt%且更佳不超過約65 wt%金屬粒子。具有此導電性金屬粒子含量之導電膠適用於形成PERC之太陽能電池上之背側焊接片。 可用作金屬粒子之金屬包括銀、銅、金、鋁、鎳、鉑、鈀、鉬中之至少一者及其混合物或合金。在較佳實施例中，金屬粒子為銀。銀可以元素銀、銀合金或銀衍生物形式存在。合適的銀衍生物包括例如銀合金及/或銀鹽，諸如鹵化銀(例如氯化銀)、氧化銀、硝酸銀、乙酸銀、三氟乙酸銀、正磷酸銀及其組合。在另一實施例中，金屬粒子可包含塗有一或多種不同金屬或合金之金屬或合金，例如塗有鋁之銀粒子或塗有銀之銅粒子。 金屬粒子可存在有有機或無機的表面塗層。此項技術中已知且視為適合於本發明之上下文的任何此類塗層均可用於金屬粒子上。較佳有機塗層為彼等促進分散入有機載體中之塗層。較佳無機塗層為彼等調節燒結且促進所得導電膠之黏著效能之塗層。若此類塗層存在，則較佳地，以金屬粒子之100%總重量計，塗層對應於不超過約5 wt%、較佳不超過約2 wt%且最佳不超過約1 wt%。 導電粒子可展現各種形狀、尺寸及比表面積。形狀之一些實例包括但不限於球形、角形、細長(桿或針狀)及扁平(片狀)。導電金屬粒子亦可以具有不同形狀之粒子之組合形式存在，諸如(例如)球形金屬粒子與片形金屬粒子之組合。 金屬粒子之另一特徵為其平均粒度d50
。d50
為中值直徑或粒度分佈之中等值。其為50%之累積分佈下的粒徑值。粒度分佈可經由雷射繞射、動態光散射、成像、電泳光散射或此項技術中已知之任何其他方法來量測。特定言之，根據ISO 13317-3:2001來測定根據本發明之粒度。如本文所闡述，使用連接至具有LA-910軟體程式之電腦的Horiba LA-910雷射繞射粒度分析器來測定中值粒徑。金屬粒子之相對折射率選自LA-910手冊且輸入軟體程式中。測試腔室用去離子水填充至貯槽上之適當填充線。接著藉由使用軟體程式中之循環及攪動功能來循環溶液。一分鐘之後，排乾溶液。額外重複此過程一次以確保腔室中無任何殘餘物質。隨後第三次用去離子水填充腔室且使其循環且攪動一分鐘。溶液中之任何背景粒子藉由使用軟體中之空白功能來排除。接著開始超音波攪動，且將金屬粒子緩慢添加至測試腔室中之溶液中直至透射率條處於軟體程式中之適當區域。一旦透射率處於正確程度，立即進行雷射繞射分析且量測金屬組分之粒度分佈且以d50
之形式給出。 較佳地，金屬粒子之中值粒徑d50
為至少約0.1 µm且較佳至少約0.5 µm。同時，d50
較佳不超過約5 µm且更佳不超過約4 µm。在一個實施例中，導電膠組合物包括球形銀粒子與片形銀粒子之組合，其中球形銀粒子之d50
較佳為低於或等於約3 µm且片形銀粒子之d50
較佳為低於或等於約5 µm。 表徵粒子之形狀及表面之另一方式為藉由其比表面積來表徵。比表面積為等同於每單位質量材料總表面積、固體或總體積或截面積之固體性質。其由表面積除以質量(單位為m2
/g)或表面積除以體積(單位為m-1
)來定義。比表面積可藉由此項技術中已知之布厄特(BET，Brunauer-Emmett-Teller)法來量測。如本文所闡述，根據DIN ISO 9277:1995進行BET量測。使用根據SMART方法(具有自適應性配料速率之吸附方法)操作之Monosorb型號MS-22儀器(由Quantachrome Instruments製造)來進行量測。使用作為參考物質之氧化鋁(表面積參考物質目錄號2003，可購自Quantachrome Instruments)。製備樣品以用於在內建式脫氣台中進行分析。流動氣體(30% N2
及70% He)掃除雜質，產生吸附可出現於其上之乾淨表面。可用供應之加熱套將樣品加熱至使用者可選之溫度。數位溫度控制器及顯示器安裝在儀器正面板上。完成脫氣之後，將樣品電池轉移至分析台。快速連接配件在轉移期間自動密封樣品電池，且接著激活系統以開始分析。手動升高填充有冷卻劑之杜瓦瓶(dewar flask)，浸沒樣品電池且引起吸附。儀器在吸附完成(2至3分鐘)時進行偵檢，自動降低杜瓦瓶，且使用內建式熱風鼓風機將樣品電池緩緩加熱回至室溫。因此，脫附氣體信號顯示於數位表上且表面積直接呈現於正面板顯示器上。整個量測(吸附及脫附)循環通常需要少於六分鐘。在吸附及脫附進行時，該技術使用高靈敏度的熱導偵檢器來量測被吸附物/惰性載氣混合物之濃度變化。當藉由機載電子器件整合且與校準比較時，偵檢器提供經吸附或經脫附之氣體的體積。對於吸附量測，使用在77K下分子截面積為0.162 nm2
之N2
5.0進行計算。進行單點分析且內建式微處理器確保線性度且自動計算以m2
/g為單位之樣品之BET表面積。 根據一個實施例，金屬粒子之比表面積可為至少約0.1 m2
/g、較佳至少約0.2 m2
/g。同時，比表面積較佳不超過10 m2
/g且更佳不超過約5 m2
/g。在一個實施例中，金屬粒子之比表面積在約0.7與1.7 m2
/g之間。玻璃料
在用於形成正側太陽能電池電極之導電膠中，玻璃料充當黏著力介質，促進導電粒子與矽基板之間的黏結，且因此提供其間之良好的電接觸。特定言之，在燃燒後，習知的玻璃料蝕刻通過矽基板之表面層(例如抗反射層)以使得可在導電膠與矽晶圓之間製造有效的電接觸。 與玻璃料當在導電膠組合物中所使用時之傳統角色相反，本發明之玻璃料設計成展現最低限度的蝕刻特徵。此類玻璃料特別適用於形成PERC之太陽能電池上之背側焊接片。特定言之，本文所描述之玻璃料將對PERC之太陽能電池之背表面層(例如背面鈍化層及罩蓋層)的蝕刻降至最低，此舉反過來將對彼等層的損壞降至最小，否則會導致分流及開路電壓損耗且因此降低太陽能電池效率。如此，本發明之玻璃料設計成低蝕刻且非接觸成形玻璃。 在一個實施例中，本發明之一或多種玻璃料較佳具有低鉛含量或不含鉛，因為已知鉛對於太陽能電池上之表面層具有強蝕刻性質。如本文所闡述，以玻璃料之100%總重量計，術語「低鉛含量」係指鉛含量為至少0.5 wt%且少於約5 wt%之玻璃料，諸如少於約4 wt%、少於約3 wt%、少於約2 wt%、少於約1 wt%且少於約0.8 wt%。如本文所闡述，以玻璃料之100%總重量計，術語「不含鉛」係指鉛含量少於約0.5 wt%、較佳少於約0.4 wt%、更佳少於約0.3 wt%、更佳少於約0.2 wt%且最佳少於約0.1 wt%鉛之玻璃料。在最佳實施例中，玻璃料包含少於約0.01 wt%鉛，該鉛可以來自其他玻璃組分之附帶雜質的形式存在。在一個較佳實施例中，玻璃組合物不包括任何有意添加之鉛。 在本發明之一個態樣中，玻璃料較佳包含相對較高含量之氧化矽(SiO2
)、氧化硼(B2
O3
)及/或氧化鉍(B2
O3
)。此等氧化物通常充當玻璃成形的氧化物。在一個實施例中，以玻璃料之100%總重量計，SiO2
、B2
O3
及Bi2
O3
之總含量為至少約70 wt%且較佳至少約75 wt%。同時，以玻璃料之100%總重量計，玻璃料包含的SiO2
、B2
O3
及Bi2
O3
之總含量較佳不超過約90 wt%且較佳不超過約85 wt%。 另外，玻璃料較佳包括至少一種鹼性氧化物，諸如(例如)Na2
O、Li2
O及/或K2
O。此等鹼性氧化物通常充當降低玻璃料在升高燃燒溫度下之化學反應性之玻璃改質劑。玻璃料較佳包括此等鹼性氧化物中之至少兩者之組合，諸如Na2
O及Li2
O。在一個實施例中，以玻璃料之100%總重量計，玻璃料包括至少約5 wt%、較佳至少約8 wt%總鹼性氧化物。同時，以玻璃料之100%總重量計，玻璃料包括不超過約20 wt%、較佳不超過約15 wt%總鹼性氧化物。 玻璃料亦可包括氧化鋅(ZnO)。若玻璃料包括ZnO，則以玻璃料之100%總重量計，其以不超過15 wt%、較佳不超過10 wt%之量存在。 玻璃料進一步包括鉬氧化物(例如MoO3
)、鈮氧化物(例如Nb2
O5
)、鋁氧化物、硫氧化物、硒氧化物、碲氧化物、釩氧化物及鎢氧化物中之至少一種。在一個實施例中，以玻璃料之100%總重量計，玻璃料較佳包括至少約2 wt%且不超過約5 wt% MoO3
。若存在，則玻璃料包括少於約2wt% Nb2
O5
。 玻璃料可包括其他元素、氧化物、加熱後產生氧化物之化合物及/或其混合物。在一個實施例中，玻璃料可包括熟習此項技術者已知之其他氧化物或化合物，包括但不限於鎂、鈦、鋯、鎳、釓、銻、鈰、鋯、鈦、錳、錫、釕、鈷、鐵、銅、鍺、銦、鹼土金屬、稀土金屬、磷及鉻或其至少兩者之任何組合、可在燃燒後產生彼等金屬氧化物之化合物或前述金屬中之至少兩者之混合物、前述氧化物中之至少兩者之混合物、可在燃燒時產生彼等金屬氧化物之前述化合物中之至少兩者之混合物或兩者或超過兩者上文所提及之各者中的任一者之混合物。 本發明之較佳玻璃料為展現玻璃轉移之非晶形或部分結晶狀固體之粉末。玻璃轉移溫度Tg
為非晶形物質在加熱後自剛性固體轉換為部分流動之過冷熔體時的溫度。本發明之玻璃料之另一重要特徵為玻璃軟化點，其通常低於玻璃轉移溫度且標識超過某一任意點之玻璃開始軟化時之點。用於測定玻璃軟化溫度及玻璃轉移溫度之方法已為熟習此項技術者所熟知。特定言之，可使用DSC設備SDT Q600 (可購自TA Instruments)來測定玻璃轉移溫度Tg
，其同時記錄差示掃描熱量測定(DSC)及熱解重量分析(TGA)曲線。儀器裝備有水平平衡器及具有鉑/鉑-銠(R型)熱電偶之熔爐。所用樣品固持器為容量為約40-90 µl之氧化鋁陶瓷坩堝。為進行量測及資料評估，分別應用量測軟體Q Advantage；Thermal Advantage Release 5.4.0及Universal Analysis 2000、4.5A版Build 4.5.0.5。至於參考盤及樣品盤，使用體積為約85 µl之氧化鋁盤。將約10-50 mg之量的樣品稱重入樣品盤中，且精確度為0.01 mg。將空的參考盤及樣品盤置放在設備中，關閉烘箱且開始量測。自25℃之起始溫度至1000℃之結束溫度，採用10 K/min加熱速率。始終用氮氣(N2
5.0)吹掃儀器中之平衡器，且用合成空氣(80% N2
及20% O2
，來自Linde)吹掃烘箱，且流動速率為50 ml/min。使用上文所描述之軟體將DSC信號中之第一步驟評估為玻璃轉移，且將經測定之起始值視為Tg
之溫度。 Tg
較佳低於導電膠所需之燃燒溫度。根據本發明，較佳玻璃料之Tg
為至少約200℃且較佳至少約250℃。同時，較佳玻璃料之Tg
為不超過約900℃、較佳不超過約800℃且最佳不超過約700℃。另外，在一個實施例中，玻璃之玻璃軟化點為約400-550℃、更佳約480-530℃。在另一實施例中，玻璃之玻璃軟化點為約650-800℃、較佳約690-760℃。 熟習此項技術者熟知玻璃料粒子可展現各種形狀、尺寸及表面積與體積比。如本文所論述，玻璃粒子可展現與可由導電金屬粒子所展現之形狀相同或類似的形狀(包括長度:寬度:厚度比)。有利於所產生電極之改進電接觸之具有一種形狀或形狀組合之玻璃料粒子為較佳的。較佳地，玻璃料粒子之中值粒徑d50
(如上文關於導電金屬粒子所闡述)為至少約0.1 µm。同時，較佳地，玻璃粉之d50
不超過約10 µm、更佳不超過約5 µm且最佳不超過約3.5 µm。在一個實施例中，玻璃料粒子之比表面積為至少約0.5 m2
/g、較佳至少約1 m2
/g且最佳至少約2 m2
/g。同時，較佳地，該比表面積不超過約15 m2
/g、較佳不超過約10 m2
/g。 根據另一實施例，玻璃料粒子可包括表面塗層。此項技術中已知且視為適合於本發明之上下文的任何該塗層皆可用於玻璃料粒子。本發明之較佳塗層包括彼等促進玻璃分散於有機載體中及導電膠之改進接觸的塗層。若此類塗層存在，則較佳地，在每種情況下以玻璃料粒子之總重量計，塗層對應於不超過約10 wt%、較佳不超過約8 wt%、最佳不超過約5 wt%。 以膠之100%總重量計，導電膠包括至少約0.5 wt%、較佳至少約1 wt%且最佳至少約2 wt%玻璃料。同時。以導電膠之100%總重量計，膠較佳包括不超過約10 wt%、較佳不超過約8 wt%、更佳不超過約6 wt%且最佳不超過約5 wt%玻璃料。添加劑
較佳添加劑為除其他明確提及之組分以外的添加至膠之組分，其有助於提高膠、其產生之電極或所得太陽能電池之電氣效能。除玻璃料及載體中存在之添加劑以外，添加劑亦可獨立地存在於導電膠中。較佳添加劑包括但不限於觸變劑、黏度調節劑、乳化劑、穩定劑或pH調節劑、無機添加劑、增稠劑及分散劑或其至少兩者之組合。較佳無機的有機金屬添加劑包括但不限於Mg、Ni、Te、W、Zn、Mg、Gd、Ce、Zr、Ti、Mn、Sn、Ru、Co、Fe、Rh、V、Y、Sb、P、Cu及Cr或其至少兩者之組合，較佳為Zn、Sb、Mn、Ni、W、Te、Rh、V、Y、Sb、P及Ru或其至少兩者之組合，其氧化物、在燃燒時產生彼等金屬氧化物之化合物或前述金屬中之至少兩者之混合物、前述氧化物中之至少兩者之混合物、在燃燒時可產生彼等金屬氧化物之前述化合物中之至少兩者之混合物或兩者或超過兩者上文所提及之各者中的任一者之混合物。在較佳實施例中，導電膠包含促進黏著力之添加劑，諸如錳氧化物、鋅氧化物、鋁氧化物或鉍氧化物。 根據一個實施例，膠可包括至少約0.1 wt%一或多種添加劑。同時，以膠之100%總重量計，膠較佳包括不超過約10 wt%、較佳不超過約5 wt%且最佳不超過約2 wt%一或多種添加劑。在最佳實施例中，以膠之100%總重量計，導電膠包含不超過約1 wt%一或多種添加劑。。形成導電膠組合物
為形成導電膠，使用此項技術中已知之用於製備膠組合物的任何方法使玻璃料材料與導電金屬粒子及有機載體組合。製備之方法並非至關重要的，只要其產生均質分散之膠即可。組份可諸如用混合器混合，隨後穿過例如三輥碾磨機以製成分散之均勻膠。除同時將所有組分混合在一起以外，可例如在球磨機中將原始玻璃料材料與銀粒子共碾磨2-24小時以達成玻璃料與銀粒子之均質混合物，其接著與有機載體混合。太陽能電池
本發明亦關於一種太陽能電池。在一個實施例中，太陽能電池包含半導體基板(例如矽晶圓)及本文所描述之實施例中之任一者之導電膠組合物。 在另一態樣中，本發明係關於藉由包括以下之方法製備之太陽能電池：將本文所描述之實施例中之任一者之導電膠組合物塗覆至半導體基板(例如矽晶圓)且燃燒半導體基板。矽晶圓
在太陽能電池之其他區域中，本發明之較佳晶圓具有能夠高效率地吸收光以產生電子-電洞對且高效率地跨越邊界、較佳跨越p-n接面邊界來分離電洞與電子的區域。本發明之較佳晶圓為彼等包含由正摻雜層及背摻雜層組成之單一體之晶圓。 晶圓較佳包含經適當摻雜之四價元素、二元化合物、三元化合物或合金。在此上下文中之較佳四價元素包括但不限於矽、鍺或錫，較佳矽。較佳二元化合物包括但不限於兩種或超過兩種四價元素之組合、第III族元素與第V族元素之二元化合物、第II族元素與第VI族元素之二元化合物或第IV族元素與第VI族元素之二元化合物。較佳四價元素之組合包括但不限於兩種或超過兩種選自矽、鍺、錫或碳之元素之組合，較佳SiC。較佳第III族元素與第V族元素之二元化合物為GaAs。根據本發明之較佳實施例，晶圓為矽。明確提及矽之前述描述亦適用於本文所描述之其他晶圓組合物。 p-n接面邊界位於晶圓之正摻雜層與背摻雜層之相接處。在n型太陽能電池中，背摻雜層摻雜有電子供給n型摻雜劑，且正摻雜層摻雜有電子接收或電洞供給p型摻雜劑。在p型太陽能電池中，背摻雜層摻雜有p型摻雜劑且正摻雜層摻雜有n型摻雜劑。根據本發明之較佳實施例，藉由首先提供經摻雜之矽基板且隨後向彼基板之一個面施加相反類型之摻雜層來製備具有p-n接面邊界之晶圓。 經摻雜之矽基板可藉由此項技術中已知且視為適合於本發明的任何方法來製備。本發明矽基板之較佳來源包括但不限於單晶矽、多晶矽、非晶矽及升級冶金矽，最佳為單晶矽或多晶矽。摻雜以形成經摻雜之矽基板可藉由在製備矽基板期間添加摻雜劑來同時進行，或其可在後續步驟中進行。在製備矽基板後之摻雜可例如藉由氣體擴散磊晶法(gas diffusion epitaxy)來進行。經摻雜之矽基板亦可容易地商購獲得。根據一個實施例，矽基板之初始摻雜可藉由向矽混合物添加摻雜劑來與矽基板形成同時進行。根據另一實施例，若存在，則正摻雜層及高度摻雜之背層之塗覆可藉由氣相磊晶法來進行。此氣相磊晶法較佳在至少約500℃、較佳至少約600℃且最佳至少約650℃之溫度下進行。同時，溫度較佳不超過約900℃、較佳不超過約800℃且最佳不超過約750℃。氣相磊晶法較佳在至少約2 kPa、較佳至少約10 kPa且最佳至少約40 kPa之壓力下進行。同時，壓力較佳不超過約100 kPa、較佳不超過約80 kPa且最佳不超過約70 kPa。 此項技術中已知，矽基板可展現多種形狀、表面紋理及尺寸。僅舉幾例，基板之形狀可包括立方形、圓盤、晶圓及不規則多面體。根據本發明之較佳實施例，晶圓為具有兩個類似、較佳相等之維度及顯著小於其他兩個維度之第三維度的立方體。第三維度可比前兩個維度小至少100倍。另外，具有粗糙表面之矽基板為較佳的。一種評定基板粗糙度之方式為評估基板次表面之表面粗糙度參數，該次表面比基板之總表面積小，較佳為小於約總表面積之一百分之一，且其為基本上平面的。表面粗糙度參數值藉由次表面面積與理論表面面積之比率給出，該理論表面係藉由將彼次表面投影至藉由使均方移位最小化而與次表面最佳擬合之平坦平面上來形成。較高表面粗糙度參數值指示較粗糙且較不規則的表面，且較低表面粗糙度參數值指示較光滑且較平坦的表面。根據本發明，矽基板之表面粗糙度較佳經修改以便在包括但不限於光吸收及對表面之黏著力的多種因素之間產生最佳平衡。 可改變矽基板之兩個較大維度以適合所得太陽能電池所需之塗覆。根據本發明，矽晶圓之厚度較佳低於約0.5 mm、更佳低於約0.3 mm且最佳低於約0.2 mm。一些晶圓之最小厚度為0.01 mm或大於0.01 mm。 正摻雜層較佳比背摻雜層薄。正摻雜層之厚度亦較佳為至少約0.1 µm且較佳不超過約10 µm，較佳不超過約5 µm且最佳不超過約2 µm。摻雜劑
較佳摻雜劑為彼等當添加至矽晶圓時藉由將電子或電洞引入能帶結構中來形成p-n接面邊界的摻雜劑。較佳地，此等摻雜劑之身分及濃度經特定選擇以便視需要調諧p-n接面之能帶結構概況且設定光吸收及導電性概況。較佳p型摻雜劑包括但不限於彼等向矽晶圓能帶結構添加電洞之摻雜劑。此項技術中已知且據認為適合於本發明之上下文的所有摻雜劑均可用作p型摻雜劑。較佳p型摻雜劑包括但不限於三價元素，特別為彼等週期表之第13族之三價元素。在此上下文中之較佳的週期表之第13族元素包括但不限於硼、鋁、鎵、銦、鉈或其至少兩者之組合，其中硼為特別較佳的。 較佳n型摻雜劑為彼等向矽晶圓能帶結構中添加電子之n型摻雜劑。較佳n型摻雜劑為週期表之第15族之元素。在此上下文中之較佳的週期表之第15族元素包括但不限於氮、磷、砷、銻、鉍或其至少兩者之組合，其中磷為特別較佳的。 如上文所描述，可改變p-n接面之各種摻雜程度以便調諧所得太陽能電池之所需性質。摻雜程度係使用次級離子質譜分析來量測。 根據某些實施例，半導體基板(亦即矽晶圓)展現高於約60 Ω/□之薄層電阻，諸如高於約65 Ω/□、70 Ω/□、90 Ω/□或100 Ω/□。為量測經摻雜之矽晶圓表面之薄層電阻，使用配備有軟體套件「GP-4 Test 1.6.6 Pro」之裝置「GP4-Test Pro」(獲自GP Solar GmbH)。為進行量測，應用四點量測原理。兩個外部探針應用恆定電流且兩個內部探針量測電壓。使用歐姆定律(Ohmic law)以Ω/□為單位導出薄層電阻。為測定平均薄層電阻，對晶圓之25個相等分佈之點進行量測。在溫度為22±1℃之空調房間中，在量測之前平衡所有設備及材料。為進行量測，「GP-Test.Pro」配備有具有銳利尖端之4點量測頭(零件號04.01.0018)以便穿透抗反射及/或鈍化層。施加10 mA電流。使量測頭與非金屬化晶圓材料接觸且開始量測。在量測晶圓上之25個相等分佈之點後，以Ω/□為單位計算平均薄層電阻。太陽能電池結構
根據本發明之方法獲得之太陽能電池有助於達成上文所描述之目的中之至少一個。本發明之較佳太陽能電池為彼等在入射光總能量轉化成電能輸出之比例方面具有高效率之太陽能電池及彼等輕質且耐久之太陽能電池。在最低限度下，太陽能電池包括：(i)前電極、(ii)正摻雜層、(iii) p-n接面邊界、(iv)背摻雜層及(v)焊接墊。如本文所闡述，太陽能電池亦可包括附加層，特別PERC之太陽能電池。抗反射層
根據本發明，在將電極施加至太陽能電池之正面之前，可施加抗反射層作為外層。在一個實施例中，抗反射層亦可同樣施加至太陽能電池之背表面。可採用此項技術中已知且視為適合於本發明之上下文中的所有抗反射層。較佳抗反射層為彼等降低由正面反射之入射光之比例且增加穿過正面待由晶圓吸收之入射光之比例的抗反射層。產生有利吸收/反射比、易經受導電膠蝕刻、以其它方式對燃燒導電膠所需之溫度具有抗性且不使電極界面附近之電子與電洞之再組合增加之抗反射層為較佳的。較佳抗反射層包括但不限於SiNx
、SiO2
、Al2
O3
、TiO2
或其至少兩者之混合物及/或其至少兩個層之組合。根據較佳實施例，抗反射層為SiNx
，詳言之其中採用矽晶圓。 抗反射層之厚度適合於適當光之波長。根據本發明之較佳實施例，抗反射層之厚度為至少20 nm、較佳至少40 nm且最佳至少60 nm。同時，厚度較佳不超過約300 nm、更佳不超過約200 nm且最佳不超過約90 nm。鈍化層
一或多個鈍化層可作為外層塗覆至矽晶圓之正側及/或背側。可在前電極形成之前或在塗覆抗反射層(若存在抗反射層)之前塗覆一或多個正鈍化層。通常在生產晶圓期間諸如經過電漿氣相沈積技術塗覆一或多個背側鈍化層。在生產PERC之太陽能電池期間，首先塗覆正抗反射層，接著塗覆背面鈍化層，最後塗覆背面罩蓋層。 較佳鈍化層為彼等降低在電極界面附近之電子/電洞再結合速率之鈍化層。可採用此項技術中已知且視為適合於本發明之上下文中的任何鈍化層。本發明之較佳鈍化層包括但不限於氧化鋁(例如Al2
O3
)。鈍化層之厚度較佳為至少0.1 nm、較佳至少10 nm且最佳至少30 nm。同時，厚度較佳不超過約2 µm、較佳不超過約1 µm且最佳不超過約200 nm。額外的保護層
除上述層以外，可添加其他層以用於機械及化學保護。可對電池進行封裝以提供化學保護。根據較佳實施例，若此類封裝存在，則使用常常稱作透明熱塑性樹脂之透明聚合物作為封裝材料。在此上下文中之較佳透明聚合物為矽橡膠及聚乙烯乙酸乙烯酯(PVA)。亦可向太陽能電池之正面添加透明玻璃片以為電池之正面提供機械保護。可將背保護材料添加至太陽能電池之背面以提供機械保護。較佳背保護材料為彼等具有良好的機械性質及耐候性之背保護材料。本發明之較佳背保護材料為具有聚氟乙烯層之聚對苯二甲酸乙二酯。背保護材料較佳存在於封裝層之下方(在背保護層與封裝兩者均存在之情況下)。 太陽能電池外部可添加框架材料以得到機械支撐。框架材料為此項技術中熟知的，且可採用視為適合於本發明之上下文中的任何框架材料。本發明之較佳框架材料為鋁。製備 PERC 之太陽能電池之方法
如下製備PERC之太陽能電池。首先，在矽基板上形成如上文所闡述之正側擴散層。在基板正側上，接著塗覆抗反射塗層，諸如彼等本文所揭示之抗反射塗層。隨後，諸如藉由電漿氣相沈積將諸如氧化鋁層之背面鈍化層塗覆至基板背表面。接著可將諸如氮化矽罩蓋層之附加背面層塗覆至背面鈍化層之上。隨後，移除部分背面鈍化層及附加背面層以曝露底層基板之區域。此步驟可藉由例如酸蝕刻或雷射鑽孔來達成。接著將鋁導電膠塗覆至背面層之上，由此填充藉由移除部分背面鈍化層產生之「洞」。在此等區域中，當燃燒鋁膠時形成局部背表面場。可在塗覆鋁膠之前或之後將背側焊接片施加至背表面上。同時亦根據此項技術中已知之習知方法形成具有背側焊接片之正側電極。例示性PERC之太陽能電池說明於圖2中。在此等圖式中，術語「AR」係指抗反射層，術語「BSF」係指背表面場，術語「AlOx
」係指氧化鋁背面鈍化層，術語「SiNx
」係指背面罩蓋層，術語「背面Al」係指背面鋁膠且術語「背面Ag」係指背側焊接片。導電膠可以此項技術中已知且視為適合於本發明之上下文中的任何方式塗覆。實例包括但不限於浸滲、浸漬、傾倒、滴落、注入、噴灑、刮刀塗佈、簾式塗佈、刷塗或印刷或其至少兩者之組合。較佳印刷技術為噴墨印刷、網版印刷、移動印刷、平版印刷、凸版印刷或模板印刷或其至少兩者之組合。根據本發明，正側及背側導電膠較佳藉由印刷、較佳藉由網版印刷來塗覆。特定言之，篩網較佳具有直徑為約40 µm或小於40 µm(例如約35 µm或小於35 µm、約30 µm或小於30 µm)之網孔。同時，篩網較佳具有直徑為至少10 µm之網孔。接著使基板經受一或多個熱處理步驟，諸如(例如)習知的經乾燥、紅外線或紫外線固化及/或燃燒。在一個實施例中，基板可根據適當概況燃燒。燃燒使經印刷之導電膠燒結以便形成固體電極。燃燒為此項技術中熟知的，且可以視為適合於本發明之上下文中的任何方式來實現。燃燒較佳在高於玻璃料材料之Tg
下進行。根據本發明，設定用於燃燒之最高溫度低於約1000℃、較佳低於約900℃。已採用溫度設定低至約800℃之熔爐以用於獲得太陽能電池。燃燒溫度亦應允許達成金屬粒子之有效燒結。通常設定燃燒溫度分佈以便使來自導電膠組合物之有機材料能燃盡。燃燒步驟通常在空氣中或在帶式熔爐中之含氧氛圍下執行。燃燒較佳以快速燃燒方法進行，且總燃燒時間為至少30秒且較佳至少40秒。同時，燃燒時間較佳不超過約3分鐘、更佳不超過約2分鐘且最佳不超過約1分鐘。晶圓溫度高於600℃之時間最佳在約3秒至7秒範圍內。基板可持續約1至5秒之時間段達到在約700至975℃範圍內之峰值溫度。燃燒亦可以例如約100-700 cm/min之高傳輸率進行，且所得滯留時間為約0.5至3分鐘。多個溫度區(例如3-12個區)可用於控制所需熱分佈。 導電膠正面及背面上之燃燒可同時或依序進行。若塗覆至兩個面之導電膠具有類似、較佳相同的最佳燃燒條件，則同時燃燒為適當的。在適當之情況下，燃燒較佳同時進行。在依序進行燃燒之情況下，較佳首先塗覆且燃燒背導電膠，隨後將導電膠塗覆且燃燒至基板正面。量測導電膠之性質
使用來自Halm Elektronik GmbH之商用IV-測試儀「cetisPV-CTL1」來量測太陽能電池之電氣效能。在電量測期間，量測設備之所有部件以及待測試之太陽能電池均保持在25℃下。在實際量測期間，應藉由溫度探針同時在電池表面上量測此溫度。Xe弧光燈以1000 W/m2
之已知AM1.5強度在電池表面上模擬日光。為使模擬器達到此強度，在短時間段內使燈快閃若干次直至其達到由IV-測試儀之「PVCTControl 4.313.0」軟體所監測之穩定程度。Halm IV測試儀使用多點接觸法來量測電流(I)及電壓(V)以確定太陽能電池之IV曲線。為進行此過程，以一定方式將太陽能電池置放於多點接觸探針之間以使得探針指針與太陽能電池之匯流排(亦即印刷線)接觸。接觸探針線之數目調節至電池表面上匯流排之數目。所有電值自動藉由所實施之軟體套件由此曲線來直接測定。作為參考標準，測試由相同面積維度、相同晶圓材料組成且使用相同正側版面加工之來自ISE Freiburg之校準太陽能電池且將資料與合格值進行比較。量測至少五個以完全相同方式加工之晶圓且藉由計算各值之平均值來解釋資料。軟體PVCTControl 4.313.0提供用於效率(Eta)、填充因數(FF)、短路電流(Jsc)、串聯電阻(Rs)及開路電壓(Voc)之值。太陽能電池模組
可將複數個本發明之太陽能電池在空間上配置且電連接以形成稱作模組之集合配置。本發明之較佳模組可具有多個配置，較佳為稱作太陽能板之矩形配置。極多種電連接太陽能電池之方式以及極多種機械配置及固定該等電池以形成集合配置之方式在此項技術中眾所周知。本發明之較佳方法為彼等產生低質量與功率輸出比率、低體積與功率輸出比率及高耐久性之方法。鋁為用於機械固定本發明之太陽能電池之較佳材料。 在一個實施例中，多個太陽能電池串聯及/或並聯連接且最初電池與最末電池之電極端部較佳連接至輸出接線。將電池接頭接合至其中已形成背側焊接片之區域。太陽能電池通常封裝於透明熱塑膠樹脂中，諸如矽橡膠或乙烯乙酸乙烯酯。將透明玻璃片置放於封裝透明熱塑膠樹脂之正表面上。將例如塗有聚氟乙烯膜之聚對苯二甲酸乙二酯片之背保護材料置放於封裝熱塑膠樹脂下。此等分層材料可在適當真空熔爐中加熱以移除空氣，且接著藉由加熱及壓製整合入一個主體中。此外，由於太陽能電池通常長期露天置放，因此需要用由鋁或其類似物組成之框架材料覆蓋太陽能電池之周邊。 本發明現將結合以下非限制性實例進行描述。實例 1
根據下表1中所闡述之組成製備第一組例示性導電膠組合物及參考導電膠組合物。所有值均以按膠組合物之100%總重量計的重量百分比形式提供。以玻璃料之100%總重量計，各個膠中之玻璃料由約75.5 wt% (SiO2
+B2
O3
+Bi2
O3
)、約13 wt%一或多種鹼金屬氧化物、約9.6 wt% ZnO及約1.9 wt% Nb2
O5
形成。表 1. 例示性膠調配物
接著在PERC晶圓背側上印刷例示性膠調配物中之各者以形成背側焊接片。在此實例中，使用具有在約35 µm線直徑及5 µm EOM下之280網狀不鏽鋼線之篩網將標準正側膠(由賓夕法尼亞州西康舍霍肯的Heraeus Precious Metals North America Conshohocken LLC製造之SOL9621E)網版印刷至PERC晶圓正側以形成指針線及匯流排。所用PERC晶圓係購自臺灣宜蘭的Sunrise Global Solar Energy Co., Ltd. (晶圓1)及俄勒岡希爾斯伯勒的SolarWorld Americas Inc.(晶圓2)。PERC晶圓已具有塗覆至其背側之局部開放的背面鈍化層。至於彼情況，將實例1之例示性膠及參考膠印刷至背表面上以形成延伸跨越電池全長且寬為約3.5 mm且長度為1.53 mm之背側焊接片。接著，將市售鋁背側膠(由中國廣東的Guangzhou Ruxing Technology Development Co., Ltd. 製造之RUX28K30)印刷在晶圓背側上方以在背面鈍化層之局部開放區域中形成鋁背表面場且略微地交疊背側焊接片。隨後在適當溫度下乾燥電池。隨後在約700-975℃之峰值溫度下燃燒具有經印刷之正側及背側膠的矽基板。 接著根據本文所闡述之參數進行例示性PERC之太陽能電池中之各者的電測試。下表2中提供電氣效能結果。所有資料已基於參考膠資料相對於100標準化。如可見，相較於參考膠組合物，兩個例示性膠調配物均展現改進的開路電壓(Voc)。因此，無論使用哪種類型聚矽氧油，皆顯示其存在改進膠組合物之電氣效能。表 2 . 例示性膠組合物之電氣效能 實例 2
根據下表3中所闡述之組成製備第二組例示性膠。所有值均以按膠組合物之100%總重量計的重量百分比形式提供。以玻璃料之100%總重量計，此等膠中之各者之玻璃料由約82 wt% (SiO2
+B2
O3
+Bi2
O3
)、約10 wt%一或多種鹼金屬氧化物、約5 wt% ZnO、約1 wt% Nb2
O5
及約2 wt% MoO3
形成。矽油2與實例1中所揭示之物質相同。表 3. 例示性膠組合物
接著將例示性膠調配物中之各者印刷至PERC晶圓背側且根據實例1中所闡述之參數進行電氣效能測試。在此實例中，所用PERC晶圓係購自中國上海的JinkoSolar Holding Co., Ltd.。 下表4中提供電氣效能結果。所有資料已基於參考膠資料相對於100標準化。如可見，相較於參考膠組合物，所有例示性膠調配物均展現改進的效率(Eta，%)。表 4 . 例示性膠組合物之電氣效能
本發明之此等優點及其他優點對於熟習此項技術者而言將自前述說明書顯而易見。因此，熟習此項技術者將認識到，可在不背離本發明之廣泛發明概念的情況下對上述實施例進行改變或修改。任何特定實施例之具體尺寸僅出於說明之目的而描述。因此應理解，本發明並非限制於本文中所描述之特定實施例，而意欲包括在本發明之範疇及精神範圍內的所有改變及修改。 RELATED APPLICATIONS This is a continuation-in-part of U.S. Patent Application Serial No. Serial No. Ser. The entire contents of their application are hereby incorporated by reference. The conductive paste used to form the electrodes of the solar cell typically comprises conductive metal particles, one or more glass frits, an organic vehicle, and optionally one or more additives. The organic vehicle of the present invention is used to form a conductive paste composition for use in a backside solder tab on a solar cell having PERC having improved electrical properties. Organic Carrier The organic vehicle of the present invention provides a medium by which conductive metal particles and glass frit can be applied to the surface of the crucible to form a backside solder tab. Preferred organic vehicles are solutions, emulsions or dispersions formed from one or more solvents, preferably organic solvents, which ensure that the components of the gum are present in a dissolved, emulsified or dispersed state. It is preferred to provide an organic vehicle which provides optimum stability of the components of the electrically conductive composition and which improves the electrical performance of the resulting PERC solar cell. In one embodiment, the organic vehicle is at least about 5 wt%, preferably at least about 10 wt%, more preferably at least about 15 wt%, more preferably at least about 20 wt%, based on 100% total weight of the conductive paste composition. And preferably in an amount of at least 25 wt%, present in the electrically conductive composition. Also, the organic vehicle preferably does not exceed about 60% by weight, preferably does not exceed about 55% by weight, and more preferably does not exceed about 50% by weight based on 100% by total weight of the conductive adhesive composition. In a preferred embodiment, the organic vehicle comprises at least one polyoxyalkylene compound. The polyoxyalkylene compound is a compound having a plurality of siloxane functional groups having a Si-O-Si bond. In a preferred embodiment, the polyoxyalkylene compound is a polyoxyxane oil which is a liquid polymerized decane having an organic side chain. The use of polyoxyalkylene compounds in conductive paste compositions has been shown to minimize etching of the back surface layer of the PERC solar cell, thereby improving the open circuit voltage (Voc) and efficiency (Eta) of the PERC solar cell. Any polyoxyphthalic acid suitable for use in the conductive paste composition can be used. In a preferred embodiment, a polyoxyxene oil having a viscosity of about 1 to 40 kcps is used, preferably a viscosity of about 1-10 kcps, such as about 5 kcP of a polyoxygenated oil, or a viscosity of about 25-35 kcps. , such as a polyoxygenated oil of about 30 kcps. The viscosity is measured according to the method described herein. In one embodiment, the organic vehicle comprises at least about 0.5 wt% polyoxalate based on 100% by weight of the organic vehicle. Also, the organic vehicle comprises no more than about 20% by weight of polyoxyxylene oil, preferably no more than about 15% by weight and most preferably no more than about 13% by weight. With respect to the gel composition as a whole, the polyoxyxylene oil is preferably at least 0.1 wt% and preferably at least about 0.2 wt%, more preferably at least 0.5 wt% and most preferably at least 1 wt%, based on 100% by total weight of the conductive paste. The amount of % exists. Also, the polyoxyxane is preferably present in an amount of no more than about 10% by weight, preferably no more than about 5% by weight, based on 100% by total weight of the conductive paste. In a preferred embodiment, the polyoxyxane is preferably present in an amount of no more than about 4% by weight based on 100% by total weight of the conductive paste. In another preferred embodiment, the gum composition comprises from about 0.2 to about 3.5 wt%, preferably from about 1 to about 3 wt% polyoxalate. In one embodiment, one or more polyoxyalkylene compounds are separately incorporated into the conductive paste from an organic vehicle or any other glue component. One or more polyoxyalkylene compounds may be added together with other gum components, ie, conductive metal particles, glass frits, and an organic vehicle, or one or more polyoxyalkylene compounds may be added to the glue combination after the gum component has been combined. In. In a preferred embodiment, the one or more polyoxyalkylene compounds are mixed with at least one solvent prior to combining with the remaining organic carrier component. In one embodiment, the interaction of the solvent with the polyoxyalkylene is observed at the time of combination to determine if it is sufficiently mixed or separated. In one embodiment, the organic vehicle further comprises at least one organic solvent and at least one resin (eg, a polymer). In a preferred embodiment, the organic vehicle comprises at least one organic solvent, at least one resin, at least one polyoxyalkylene compound, or any combination thereof. Preferred resins are those which contribute to the formation of an electrically conductive composition having favorable printability and viscosity. All resins known in the art and considered suitable for the context of the present invention are useful as resins in organic vehicles. Preferred resins include, but are not limited to, polymeric resins, monomeric resins, and resins which are combinations of polymers and monomers. The polymeric resin may also be a copolymer in which at least two different monomer units are contained in a single molecule. Preferred polymer resins are resins which carry a functional group in the polymer main chain, resins which carry a functional group outside the main chain, and resins which carry a functional group in both the main chain and the main chain. Preferred polymers which carry a functional group in the main chain include, for example, polyesters, substituted polyesters, polycarbonates, substituted polycarbonates, polymers carrying a cyclic group in the main chain, glycans, substituted a polysaccharide, a polyurethane, a substituted polyurethane, a polyamine, a substituted polyamine, a phenolic resin, a substituted phenolic resin, one or more of the foregoing polymers The monomer may be combined with other copolymers of comonomers or a combination of at least two thereof. According to one embodiment, the resin may be polyvinyl butyral or polyethylene. Polymers which preferably carry a ring group in the main chain include, for example, polyvinylbutylate (PVB) and derivatives thereof, and polyterpineol and derivatives thereof, or mixtures thereof. Preferred glycans include, for example, cellulose and alkyl derivatives thereof, preferably methylcellulose, ethylcellulose, hydroxyethylcellulose, propylcellulose, hydroxypropylcellulose, butylcellulose, and a derivative thereof and a mixture of at least two thereof. Other preferred polymers include, for example, cellulose ester resins such as cellulose acetate propionate, cellulose acetate butyrate, and any combination thereof. Preferred polymers which carry functional groups outside the main polymer chain include those which carry a guanamine group, which are often referred to as acrylic resins, which carry an acid and/or ester group or which carry a combination of the aforementioned functional groups. The polymer or a combination thereof. Polymers preferably carrying a guanamine outside the main chain include, for example, polyvinylpyrrolidone (PVP) and derivatives thereof. Polymers preferably carrying an acid and/or ester group outside the main chain include, for example, polyacrylic acid and derivatives thereof, polymethacrylate (PMA) and derivatives thereof or polymethyl methacrylate (PMMA) and derivatives thereof. Or a mixture thereof. Preferred monomer resins are ethylene glycol based monomers, terpineol resins or rosin derivatives or mixtures thereof. Preferably, the ethylene glycol-based monomer resin is a resin having a plurality of ether groups, a plurality of ester groups, or a resin having an ether group and an ester group, and preferably the ether group is a methyl group or an ethyl group. The propyl group, the butyl group, the pentyl group, the hexyl group and the higher alkyl ether are preferred. The preferred ester group is an acetate and an alkyl derivative thereof, preferably ethylene glycol monobutyl ether monoacetate, or a mixture thereof. Pine resin gum resin, polyvinyl butyrate and ethyl cellulose are the best resins. In one embodiment, ethyl cellulose is used as a binder. The resin may be present in an amount of at least about 0.5 wt%, preferably at least about 1 wt%, and most preferably at least about 3 wt%, based on 100% by total weight of the organic vehicle. Also, the resin may be present in an amount of no more than about 10% by weight and preferably no more than about 8% by weight based on 100% by weight of the organic vehicle. In one embodiment, the resin is present in an amount of about 5 wt% based on 100% by total weight of the organic vehicle. Preferred solvents are those which are removed from the gel to a significant extent during combustion. Preferably, the absolute weight exhibited after combustion is reduced by at least about 80% compared to prior to combustion, preferably by at least about 95% compared to prior to combustion. Preferred solvents are those which contribute to the advantageous viscosity and printability characteristics. All solvents known in the art and considered suitable for the context of the present invention are useful as solvents in organic vehicles. Preferred solvents are those which are present in liquid form at standard ambient temperature and pressure (SATP) (298.15 K, 25 ° C, 77 ° F), 100 kPa (14.504 psi, 0.986 atm), preferably with a high boiling point. A solvent having a melting point above about -20 ° C at about 90 ° C. Preferred solvents are polar or non-polar, protic or aprotic, aromatic or non-aromatic. Preferred solvents include, for example, monoalcohols, diols, polyalcohols, monoesters, diesters, polyesters, monoethers, diethers, polyethers, at least one or more of these functional groups, and optionally other classes Functional group (preferably a cyclic group, an aromatic group, an unsaturated bond, an alcohol group in which one or more O atoms are replaced by a hetero atom, an ether group in which one or more O atoms are replaced by a hetero atom, or one or more O atoms) A solvent of a hetero atom-substituted ester group) and a mixture of two or more of the foregoing solvents. Preferred esters in this context include, for example, dialkyl esters of adipic acid, preferably the alkyl component is methyl, ethyl, propyl, butyl, pentyl, hexyl and higher alkyl or two different The combination of iso-alkyl groups is preferably a mixture of dimethyl adipate and two or more than two adipates. Preferred ethers in this context include, for example, diethers, preferably dialkyl ethers of ethylene glycol, preferably the alkyl component is methyl, ethyl, propyl, butyl, pentyl, hexyl and higher alkyl. Or a combination of two different such alkyl groups and a mixture of two diethers. Preferred alcohols in this context include, for example, primary, secondary and tertiary alcohols, preferably tertiary alcohols, preferably terpineols and derivatives thereof, or mixtures of two or more than two alcohols. A preferred solvent for combining more than one different functional group is 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (commonly known as texanol) and its derivatives; 2-(2-B Oxyethoxyethoxy)ethanol (often referred to as carbitol), an alkyl derivative thereof, preferably methyl, ethyl, propyl, butyl, pentyl and hexyl carbitol, preferably hexyl carbitol Or butyl carbitol, and its acetate derivative, preferably butyl carbitol acetate; or a mixture of at least two of the foregoing. In a preferred embodiment, the solvent comprises at least one of butyl carbitol, butyl carbitol acetate, terpineol or a mixture thereof. It is believed that these three solvents are thoroughly mixed with the polyoxyalkylene compound. The organic solvent may be present in an amount of at least about 50 wt% and more preferably at least about 60 wt% and more preferably at least about 70 wt%, based on 100% by total weight of the organic vehicle. Also, the organic solvent may be present in an amount of no more than about 95 wt% and more preferably no more than about 90 wt%, based on 100% by total weight of the organic vehicle. Surfactants known in the art can be used with one or more polyoxyalkylene compounds. Suitable surfactants are those which help to form an electrically conductive composition having advantageous printability and viscosity characteristics. All surfactants known in the art and considered suitable for the context of the present invention are useful as surfactants in organic vehicles. Preferred surfactants are those based on linear, branched, aromatic, fluorinated, polyether chains, and combinations thereof. Preferred surfactants include, but are not limited to, single chain, double chain or multi chain polymers. Preferred surfactants can have nonionic, anionic, cationic, amphiphilic or zwitterionic heads. Preferred surfactants can be polymeric surfactants and monomeric surfactants or mixtures thereof. Preferred surfactants may have a pigment affinity group, preferably a hydroxy-functional carboxylic acid ester having a pigment affinity group (e.g., DISPERBYK®-108, manufactured by BYK USA, Inc.), an acrylate copolymer having a pigment affinity group ( For example, DISPERBYK®-116, manufactured by BYK USA, Inc., modified polyether with pigment affinity (such as TEGO® DISPERS 655, manufactured by Evonik Tego Chemie GmbH) and other surfactants with high pigment affinity groups (eg Duomeen TDO®, manufactured by Akzo Nobel NV). Other preferred polymers not included in the above list include, but are not limited to, polyethylene oxide, polyethylene glycol and derivatives thereof, and alkyl carboxylic acids and derivatives or salts thereof, or mixtures thereof. A preferred polyethylene glycol derivative is poly(ethylene glycol) acetic acid. Preferred alkyl carboxylic acids are those alkyl carboxylic acids having fully saturated alkyl chains and alkyl carboxylic acids having monounsaturated or polyunsaturated alkyl chains, or mixtures thereof. Preferably, the carboxylic acid having a saturated alkyl chain is a carboxylic acid having an alkyl chain length in the range of from about 8 to about 20 carbon atoms, preferably C 9 H 19 COOH (capric acid), C 11 H 23 COOH (lauric acid), C 13 H 27 COOH (myristic acid), C 15 H 31 COOH (palmitic acid), C 17 H 35 COOH (stearic acid) or a salt or a mixture thereof. Preferred carboxylic acids having an unsaturated alkyl chain are C 18 H 34 O 2 (oleic acid) and C 18 H 32 O 2 (linolenic acid). If present, the one or more additional surfactants can be at least about 0.5 wt% based on 100% by weight of the organic vehicle. Also, the surfactant is preferably no more than about 10% by weight and preferably no more than about 8% by weight based on 100% by weight of the total weight of the organic vehicle. The organic vehicle may also contain one or more thixotropic agents and/or other additives. Any thixotropic agent known to those skilled in the art can be used with the organic vehicle of the present invention. For example, without limitation, the thixotropic agent can be derived from a natural source or it can be synthesized. Preferred thixotropic agents include, but are not limited to castor oil and derivatives thereof, inorganic clays, polyamide and derivatives thereof, fumed silicon dioxide, carboxylic acid derivatives, preferably fatty acid derivative (e.g. C 9 H 19 COOH (Citrate), C 11 H 23 COOH (lauric acid), C 13 H 27 COOH (myristic acid), C 15 H 31 COOH (palmitic acid), C 17 H 35 COOH (stearic acid), C 18 H 34 O 2 (oleic acid), C 18 H 32 O 2 (linolenic acid), or a combination thereof. May also be used commercially available thixotropic agent, such as (e.g.) Thixotrol ® MAX, Thixotrol ® ST or THIXCIN ® E. According to one embodiment, the organic vehicle comprises at least about 1 wt% and preferably at least about 7 wt% of the thixotropic agent, based on 100% by total weight of the organic vehicle. Also, the organic vehicle preferably comprises no more than about 20% by weight, preferably no more than about 15% by weight, of the thixotropic agent, based on 100% by weight of the total weight of the organic vehicle. The additives in the preferred organic vehicle are those which differ from the foregoing components and which contribute to the advantageous properties of the electrically conductive composition, such as improved electrical performance and stability characteristics. Additives known in the art and believed to be suitable for the context of the present invention may be used. Preferred additives include, but are not limited to, viscosity modifiers, stabilizers, inorganic additives, thickeners, emulsifiers, dispersants, and pH adjusters. If present, the additives preferably do not exceed about 15% by weight based on 100% by weight of the organic vehicle. The formulation of the organic vehicle affects the viscosity of the conductive adhesive composition, which in turn affects its printability. If the viscosity is too high, the glue does not transfer well through the mesh and may be broken or lower. If the viscosity is too low, the glue may be too fluid, causing the printed line to expand and the aspect ratio to decrease. To measure the viscosity of any of the gel components, a Brookfield HBDV-III Digital Rheometer equipped with a CP-44Y sample cup and a #51 cone (Brookfield HBDV-III Digital Rheometer) was used. ). The sample temperature was maintained at 25 ° C using a TC-502 circulating temperature bath. Set the measurement gap to 0.026 mm and the sample volume to approximately 0.5 ml. The sample was allowed to equilibrate for two minutes and then a constant rotational speed of 1.0 rpm was applied for one minute. The viscosity of the sample after this interval is reported in units of kcps. Conductive Metal Particles The conductive composition also contains conductive metal particles. Preferred conductive metal particles are conductive metal particles which exhibit optimum conductivity and are effectively sintered after combustion so that they produce electrodes having high conductivity. Preferred conductive metal particles suitable for forming solar cell electrodes are known in the art. Preferred metal particles include, but are not limited to, elemental metals, alloys, metal derivatives, mixtures of at least two metals, mixtures of at least two alloys, or mixtures of at least one metal and at least one alloy. In an embodiment of the invention, the conductive paste may comprise at least about 30 wt%, preferably at least about 35 wt%, more preferably at least about 40 wt%, more preferably at least about 45 wt%, based on 100% by total weight of the gum. And preferably at least about 50 wt% metal particles. In a preferred embodiment, the conductive paste comprises at least about 60 wt% metal particles based on 100% by weight of the gum. Also, the conductive paste preferably comprises no more than about 99 wt%, preferably no more than about 95 wt%, more preferably no more than about 90 wt%, more preferably no more than about 85 wt%, based on 100% by total weight of the gum composition. More preferably, it does not exceed about 80 wt%, more preferably does not exceed about 75 wt%, more preferably does not exceed about 70 wt%, and more preferably does not exceed about 65 wt% of metal particles. The conductive paste having the content of the conductive metal particles is suitable for forming the back side soldering piece on the solar cell of the PERC. Metals useful as metal particles include at least one of silver, copper, gold, aluminum, nickel, platinum, palladium, molybdenum, and mixtures or alloys thereof. In a preferred embodiment, the metal particles are silver. Silver may be present in the form of elemental silver, silver alloy or silver derivatives. Suitable silver derivatives include, for example, silver alloys and/or silver salts such as silver halides (e.g., silver chloride), silver oxide, silver nitrate, silver acetate, silver trifluoroacetate, silver orthophosphate, and combinations thereof. In another embodiment, the metal particles may comprise a metal or alloy coated with one or more different metals or alloys, such as silver particles coated with aluminum or copper particles coated with silver. Metal particles may be present with an organic or inorganic surface coating. Any such coating known in the art and considered suitable for the context of the present invention can be used on metal particles. Preferred organic coatings are those which promote dispersion into the organic vehicle. Preferred inorganic coatings are those which adjust the sintering and promote the adhesion of the resulting conductive paste. If such a coating is present, preferably, the coating corresponds to no more than about 5% by weight, preferably no more than about 2% by weight, and most preferably no more than about 1% by weight, based on 100% by total weight of the metal particles. . The conductive particles can exhibit a variety of shapes, sizes, and specific surface areas. Some examples of shapes include, but are not limited to, spherical, angular, elongated (rod or needle), and flat (sheet). The conductive metal particles may also be present in a combination of particles having different shapes, such as, for example, a combination of spherical metal particles and sheet metal particles. Another feature of the metal particles is their average particle size d 50 . d 50 is the median diameter or the equivalent of the particle size distribution. It is a particle size value under a cumulative distribution of 50%. The particle size distribution can be measured via laser diffraction, dynamic light scattering, imaging, electrophoretic light scattering, or any other method known in the art. In particular, the particle size according to the invention is determined according to ISO 13317-3:2001. The median particle size was determined using a Horiba LA-910 laser diffraction particle size analyzer connected to a computer with the LA-910 software program as described herein. The relative refractive index of the metal particles is selected from the LA-910 manual and entered into the software program. The test chamber is filled with deionized water to the appropriate fill line on the sump. The solution is then circulated by using the cycle and agitation functions in the software program. After one minute, drain the solution. This process is repeated an additional time to ensure that there is no residual material in the chamber. The chamber was then filled with deionized water for the third time and allowed to circulate and agitate for one minute. Any background particles in the solution are excluded by using the blank function in the software. Ultrasonic agitation is then initiated and metal particles are slowly added to the solution in the test chamber until the transmittance strip is in the appropriate region of the software program. Once the transmittance is at the correct level, laser diffraction analysis is performed immediately and the particle size distribution of the metal component is measured and given in the form of d 50 . Preferably, the metal particles have a median particle size d 50 of at least about 0.1 μm and preferably at least about 0.5 μm. At the same time, d 50 is preferably no more than about 5 μm and more preferably no more than about 4 μm. In one embodiment, the conductive paste composition comprises a combination of spherical silver particles and flake-shaped silver particles, wherein the spherical silver particles preferably have a d 50 of less than or equal to about 3 μm and the d 50 of the tabular silver particles is preferably Less than or equal to about 5 μm. Another way to characterize the shape and surface of a particle is by its specific surface area. The specific surface area is a solid property equivalent to the total surface area, solid or total volume or cross-sectional area per unit mass of material. It is defined by the surface area divided by mass (in m 2 /g) or surface area divided by volume (in m -1 ). The specific surface area can be measured by the BET (Brunauer-Emmett-Teller) method known in the art. As described herein, BET measurements were performed in accordance with DIN ISO 9277:1995. The Monosorb model MS-22 instrument (manufactured by Quantachrome Instruments) operated according to the SMART method (adsorption method with adaptive dosing rate) was used for measurement. Alumina was used as a reference material (surface area reference material catalog number 2003, available from Quantachrome Instruments). Samples were prepared for analysis in a built-in degassing station. The flowing gas (30% N 2 and 70% He) sweeps away impurities, creating a clean surface on which adsorption can occur. The sample can be heated to a user selectable temperature using a supplied heating mantle. The digital temperature controller and display are mounted on the front panel of the instrument. After the degassing is completed, the sample cells are transferred to the analysis station. The quick connect accessory automatically seals the sample battery during transfer and then activates the system to begin the analysis. The dewar bottle filled with coolant was manually raised, immersed in the sample cell and caused to adsorb. The instrument detects when the adsorption is complete (2 to 3 minutes), automatically reduces the Dewar, and slowly heats the sample battery back to room temperature using a built-in hot air blower. Thus, the desorption gas signal is displayed on the digital display and the surface area is presented directly on the front panel display. The entire measurement (adsorption and desorption) cycle typically takes less than six minutes. This technique uses a highly sensitive thermal conductivity detector to measure changes in the concentration of the adsorbate/inert carrier gas mixture as adsorption and desorption are performed. The detector provides the volume of the adsorbed or desorbed gas when integrated by the onboard electronics and compared to the calibration. For the adsorption measurement, calculation was carried out using N 2 5.0 having a molecular cross-sectional area of 0.162 nm 2 at 77K. A single point analysis was performed and the built-in microprocessor ensured linearity and automatically calculated the BET surface area of the sample in m 2 /g. According to one embodiment, the metal particles may have a specific surface area of at least about 0.1 m 2 /g, preferably at least about 0.2 m 2 /g. Meanwhile, the specific surface area is preferably not more than 10 m 2 /g and more preferably not more than about 5 m 2 /g. In one embodiment, the metal particles have a specific surface area between about 0.7 and 1.7 m 2 /g. Glass frit In the conductive paste used to form the electrodes of the positive side solar cells, the frit acts as an adhesive medium, promoting adhesion between the conductive particles and the tantalum substrate, and thus providing good electrical contact therebetween. In particular, after combustion, conventional frits are etched through a surface layer of a germanium substrate (eg, an anti-reflective layer) such that an effective electrical contact can be made between the conductive paste and the germanium wafer. In contrast to the conventional role of frit when used in conductive paste compositions, the frits of the present invention are designed to exhibit minimal etch characteristics. Such frits are particularly useful for forming backside pads on solar cells of PERC. In particular, the frit described herein minimizes the etching of the back surface layer of the PERC solar cell (eg, the back passivation layer and the cap layer), which in turn minimizes damage to their layers. Otherwise, it will cause shunt and open circuit voltage loss and thus reduce solar cell efficiency. As such, the frit of the present invention is designed to be low etched and non-contact formed glass. In one embodiment, one or more of the frits of the present invention preferably have a low lead content or no lead because lead is known to have strong etching properties for the surface layer on solar cells. As set forth herein, the term "low lead content", based on 100% by weight of the glass frit, refers to a frit having a lead content of at least 0.5 wt% and less than about 5 wt%, such as less than about 4 wt%, less. It is about 3 wt%, less than about 2 wt%, less than about 1 wt%, and less than about 0.8 wt%. As set forth herein, the term "lead-free" as used herein refers to a lead content of less than about 0.5 wt%, preferably less than about 0.4 wt%, more preferably less than about 0.3 wt%, based on 100% by total weight of the glass frit. More preferably less than about 0.2 wt% and most preferably less than about 0.1 wt% lead frit. In a preferred embodiment, the frit contains less than about 0.01 wt% lead, which may be present in the form of incidental impurities from other glass components. In a preferred embodiment, the glass composition does not include any intentionally added lead. In one aspect of the invention, the glass frit preferably comprises a relatively high level of cerium oxide (SiO 2 ), boron oxide (B 2 O 3 ), and/or cerium oxide (B 2 O 3 ). These oxides typically act as oxides for glass forming. In one embodiment, the total content of SiO 2 , B 2 O 3 , and Bi 2 O 3 is at least about 70 wt% and preferably at least about 75 wt%, based on 100% by total weight of the glass frit. Meanwhile, the total content of SiO 2 , B 2 O 3 and Bi 2 O 3 contained in the glass frit is preferably not more than about 90% by weight and preferably not more than about 85% by weight based on 100% by total weight of the glass frit. Additionally, the glass frit preferably includes at least one basic oxide such as, for example, Na 2 O, Li 2 O, and/or K 2 O. These basic oxides generally act as glass modifiers that reduce the chemical reactivity of the frit at elevated combustion temperatures. The glass frit preferably comprises a combination of at least two of such basic oxides, such as Na 2 O and Li 2 O. In one embodiment, the glass frit comprises at least about 5 wt%, preferably at least about 8 wt% total basic oxide, based on 100% by total weight of the glass frit. At the same time, the glass frit comprises no more than about 20 wt%, preferably no more than about 15 wt% total basic oxide, based on 100% by weight of the glass frit. The glass frit may also include zinc oxide (ZnO). If the glass frit comprises ZnO, it is present in an amount of no more than 15% by weight, preferably no more than 10% by weight, based on 100% by total weight of the glass frit. The glass frit further includes at least at least a molybdenum oxide (eg, MoO 3 ), a cerium oxide (eg, Nb 2 O 5 ), an aluminum oxide, a sulfur oxide, a selenium oxide, a cerium oxide, a vanadium oxide, and a tungsten oxide. One. In one embodiment, 100% of the total weight of the frit glass frit glass preferably comprises at least about 2 wt% and not more than about 5 wt% MoO 3. If present, the frit includes less than about 2 wt% Nb 2 O 5 . The frit may include other elements, oxides, compounds that produce oxides upon heating, and/or mixtures thereof. In one embodiment, the glass frit may include other oxides or compounds known to those skilled in the art including, but not limited to, magnesium, titanium, zirconium, nickel, niobium, tantalum, niobium, zirconium, titanium, manganese, tin, antimony. Any combination of cobalt, iron, copper, ruthenium, indium, alkaline earth metal, rare earth metal, phosphorus and chromium or at least two thereof, a compound which can produce such metal oxides after combustion, or at least two of the foregoing metals a mixture, a mixture of at least two of the foregoing oxides, a mixture of at least two of the foregoing compounds which may produce such metal oxides upon combustion, or both or more than each of the above mentioned a mixture of either. A preferred glass frit of the present invention is a powder which exhibits a glass transition of an amorphous or partially crystalline solid. A glass transition temperature T g of amorphous material is converted to a temperature at which part of the flow of the supercooled melt from a rigid solid after heating. Another important feature of the frit of the present invention is the point at which the glass softening point, which is generally lower than the glass transition temperature and which marks the beginning of softening of the glass beyond any point. Methods for determining the glass softening temperature and glass transition temperature are well known to those skilled in the art. Specifically, a DSC device SDT Q600 (available from TA Instruments) can be used to determine the glass transition temperature Tg , which simultaneously records differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) curves. The instrument is equipped with a horizontal balancer and a furnace with a platinum/platinum-rhodium (R-type) thermocouple. The sample holder used was an alumina ceramic crucible having a capacity of about 40-90 μl. For measurement and data evaluation, the measurement software Q Advantage; Thermal Advantage Release 5.4.0 and Universal Analysis 2000, 4.5A version Build 4.5.0.5 were applied. As for the reference disc and the sample tray, an alumina disc having a volume of about 85 μl was used. A sample of approximately 10-50 mg was weighed into the sample pan with an accuracy of 0.01 mg. Place the empty reference plate and sample tray in the unit, turn off the oven and start measuring. From a starting temperature of 25 ° C to an end temperature of 1000 ° C, a heating rate of 10 K/min was used. The balancer in the instrument was always purged with nitrogen (N 2 5.0) and the oven was purged with synthetic air (80% N 2 and 20% O 2 from Linde) at a flow rate of 50 ml/min. The first step in the DSC signal was evaluated as glass transfer using the software described above, and the measured starting value was taken as the temperature of Tg . The T g is preferably lower than the combustion temperature required for the conductive paste. Preferably, the glass frit has a Tg of at least about 200 ° C and preferably at least about 250 ° C in accordance with the present invention. At the same time, the preferred glass frit has a Tg of no more than about 900 ° C, preferably no more than about 800 ° C and most preferably no more than about 700 ° C. Additionally, in one embodiment, the glass has a softening point of from about 400 to 550 ° C, more preferably from about 480 to 530 ° C. In another embodiment, the glass has a softening point of from about 650 to 800 ° C, preferably from about 690 to 760 ° C. It is well known to those skilled in the art that glass frit particles can exhibit a variety of shapes, sizes, and surface area to volume ratios. As discussed herein, the glass particles can exhibit a shape (including length: width: thickness ratio) that is the same or similar to that exhibited by the conductive metal particles. Glass frit particles having a shape or combination of shapes that facilitate improved electrical contact of the resulting electrode are preferred. Preferably, the glass frit particle median particle size d 50 (as set forth above with respect to the conductive metal particles) is at least about 0.1 μm. Also, preferably, the glass powder has a d 50 of no more than about 10 μm, more preferably no more than about 5 μm and most preferably no more than about 3.5 μm. In one embodiment, the glass frit particles have a specific surface area of at least about 0.5 m 2 /g, preferably at least about 1 m 2 /g and most preferably at least about 2 m 2 /g. Also, preferably, the specific surface area does not exceed about 15 m 2 /g, preferably does not exceed about 10 m 2 /g. According to another embodiment, the frit particles may comprise a surface coating. Any such coating known in the art and considered suitable for the context of the present invention can be used for frit particles. Preferred coatings of the present invention include those coatings which promote dispersion of the glass in the organic vehicle and improved contact of the conductive paste. If such a coating is present, preferably, in each case, the coating corresponds to no more than about 10% by weight, preferably no more than about 8% by weight, optimally no more than the total weight of the glass frit particles. About 5 wt%. The conductive paste comprises at least about 0.5 wt%, preferably at least about 1 wt%, and most preferably at least about 2 wt% glass frit, based on 100% by weight of the gum. Simultaneously. The gum preferably comprises no more than about 10% by weight, preferably no more than about 8% by weight, more preferably no more than about 6% by weight and most preferably no more than about 5% by weight of the glass frit, based on 100% by weight of the total weight of the conductive paste. Additives Preferred additives are components added to the gum other than those specifically mentioned, which help to increase the electrical properties of the glue, the electrode from which it is produced, or the resulting solar cell. In addition to the additives present in the frit and the support, the additives may also be present independently in the conductive paste. Preferred additives include, but are not limited to, thixotropic agents, viscosity modifiers, emulsifiers, stabilizers or pH adjusters, inorganic additives, thickeners and dispersants, or combinations of at least two thereof. Preferred inorganic organometallic additives include, but are not limited to, Mg, Ni, Te, W, Zn, Mg, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Rh, V, Y, Sb, P. And Cu, Cr, or a combination of at least two thereof, preferably Zn, Sb, Mn, Ni, W, Te, Rh, V, Y, Sb, P, and Ru, or a combination of at least two thereof, an oxide thereof, a compound which produces a metal oxide or a mixture of at least two of the foregoing metals, a mixture of at least two of the foregoing oxides, and at least two of the foregoing compounds which may produce such metal oxides upon combustion. A mixture of the two or a mixture of both or more than any of the above. In a preferred embodiment, the conductive paste comprises an additive that promotes adhesion, such as manganese oxide, zinc oxide, aluminum oxide or antimony oxide. According to one embodiment, the glue may include at least about 0.1 wt% of one or more additives. Also, the gum preferably comprises no more than about 10% by weight, preferably no more than about 5% by weight and most preferably no more than about 2% by weight of one or more additives, based on 100% by weight of the gum. In a preferred embodiment, the electrically conductive paste comprises no more than about 1 wt% of one or more additives, based on 100% by weight of the gum. . Forming a Conductive Glue Composition To form a conductive paste, the frit material is combined with conductive metal particles and an organic vehicle using any method known in the art for preparing a glue composition. The method of preparation is not critical as long as it produces a homogeneously dispersed gum. The components can be mixed, for example, with a mixer, and then passed through, for example, a three-roll mill to form a dispersed uniform gel. In addition to mixing all of the components together at the same time, the original frit material can be milled with the silver particles, for example, in a ball mill for 2-24 hours to achieve a homogeneous mixture of frit and silver particles, which is then mixed with the organic vehicle. Solar Cell The present invention also relates to a solar cell. In one embodiment, a solar cell comprises a conductive substrate composition of a semiconductor substrate, such as a germanium wafer, and any of the embodiments described herein. In another aspect, the invention is directed to a solar cell prepared by a method comprising: applying a conductive paste composition of any of the embodiments described herein to a semiconductor substrate (eg, a germanium wafer) And burning the semiconductor substrate. 矽 Wafers In other regions of the solar cell, the preferred wafer of the present invention has the ability to efficiently absorb light to create electron-hole pairs and efficiently cross the boundary, preferably across the pn junction boundary to separate the holes The area with electronics. Preferred wafers of the present invention are wafers comprising a single body consisting of a positively doped layer and a back doped layer. The wafer preferably comprises a suitably doped tetravalent element, a binary compound, a ternary compound or an alloy. Preferred tetravalent elements in this context include, but are not limited to, ruthenium, osmium or tin, preferably ruthenium. Preferred binary compounds include, but are not limited to, a combination of two or more than four tetravalent elements, a binary compound of a Group III element and a Group V element, a binary compound of a Group II element and a Group VI element, or A binary compound of a Group IV element and a Group VI element. Preferred combinations of tetravalent elements include, but are not limited to, two or more than two combinations of elements selected from the group consisting of ruthenium, osmium, tin or carbon, preferably SiC. Preferably, the binary compound of the Group III element and the Group V element is GaAs. According to a preferred embodiment of the invention, the wafer is germanium. The foregoing descriptions explicitly mentioned also apply to other wafer compositions described herein. The pn junction boundary is located at the junction of the positive doped layer and the back doped layer of the wafer. In an n-type solar cell, the back doped layer is doped with electrons to supply an n-type dopant, and the positive doped layer is doped with electron accepting or holes to supply a p-type dopant. In a p-type solar cell, the back doped layer is doped with a p-type dopant and the positive doped layer is doped with an n-type dopant. In accordance with a preferred embodiment of the present invention, a wafer having a pn junction boundary is prepared by first providing a doped germanium substrate and then applying a doped layer of the opposite type to one face of the substrate. The doped germanium substrate can be prepared by any method known in the art and deemed suitable for the present invention. Preferred sources of the tantalum substrate of the present invention include, but are not limited to, single crystal germanium, polycrystalline germanium, amorphous germanium, and upgraded metallurgical germanium, most preferably single crystal germanium or polycrystalline germanium. Doping to form a doped germanium substrate can be performed simultaneously by adding a dopant during the preparation of the germanium substrate, or it can be performed in a subsequent step. The doping after the preparation of the tantalum substrate can be carried out, for example, by gas diffusion epitaxy. The doped germanium substrate can also be readily obtained commercially. According to one embodiment, the initial doping of the germanium substrate can be performed simultaneously with the germanium substrate formation by adding a dopant to the germanium mixture. According to another embodiment, the coating of the positively doped layer and the highly doped back layer, if present, can be performed by vapor phase epitaxy. The vapor phase epitaxy process is preferably carried out at a temperature of at least about 500 ° C, preferably at least about 600 ° C and most preferably at least about 650 ° C. At the same time, the temperature is preferably no more than about 900 ° C, preferably no more than about 800 ° C and most preferably no more than about 750 ° C. The vapor phase epitaxy process is preferably carried out at a pressure of at least about 2 kPa, preferably at least about 10 kPa, and most preferably at least about 40 kPa. At the same time, the pressure preferably does not exceed about 100 kPa, preferably does not exceed about 80 kPa and most preferably does not exceed about 70 kPa. It is known in the art that a tantalum substrate can exhibit a variety of shapes, surface textures, and sizes. The shape of the substrate may include cuboids, disks, wafers, and irregular polyhedrons, to name a few. In accordance with a preferred embodiment of the present invention, the wafer is a cube having two similar, preferably equal, dimensions and a third dimension that is significantly smaller than the other two dimensions. The third dimension can be at least 100 times smaller than the first two dimensions. In addition, a tantalum substrate having a rough surface is preferred. One way to assess substrate roughness is to evaluate the surface roughness parameter of the subsurface of the substrate that is less than the total surface area of the substrate, preferably less than about one percent of the total surface area, and which is substantially planar. The surface roughness parameter value is given by the ratio of the subsurface area to the theoretical surface area, which is best fitted to the subsurface by projecting the surface to the surface by minimizing the mean square displacement. Formed on the plane. Higher surface roughness parameter values indicate a coarser and less irregular surface, and lower surface roughness parameter values indicate a smoother and flatter surface. In accordance with the present invention, the surface roughness of the tantalum substrate is preferably modified to provide an optimum balance between various factors including, but not limited to, light absorption and adhesion to the surface. The two larger dimensions of the tantalum substrate can be varied to suit the desired coating of the resulting solar cell. In accordance with the present invention, the thickness of the germanium wafer is preferably less than about 0.5 mm, more preferably less than about 0.3 mm, and most preferably less than about 0.2 mm. Some wafers have a minimum thickness of 0.01 mm or more. The positive doped layer is preferably thinner than the back doped layer. The thickness of the positively doped layer is also preferably at least about 0.1 μm and preferably no more than about 10 μm, preferably no more than about 5 μm and most preferably no more than about 2 μm. Dopants Preferred dopants are dopants that form pn junction boundaries by introducing electrons or holes into the band structure when added to a germanium wafer. Preferably, the identity and concentration of such dopants are specifically selected to tune the band structure profile of the pn junction as desired and to set the light absorption and conductivity profiles. Preferred p-type dopants include, but are not limited to, dopants that add holes to the germanium wafer band structure. All dopants known in the art and believed to be suitable for the context of the present invention can be used as p-type dopants. Preferred p-type dopants include, but are not limited to, trivalent elements, particularly the trivalent elements of Group 13 of their periodic table. Preferred Group 13 elements of the periodic table in this context include, but are not limited to, boron, aluminum, gallium, indium, antimony or combinations of at least two thereof, with boron being particularly preferred. Preferred n-type dopants are n-type dopants that add electrons to the germanium wafer band structure. Preferred n-type dopants are elements of Group 15 of the periodic table. Preferred Group 15 elements of the periodic table in this context include, but are not limited to, nitrogen, phosphorus, arsenic, antimony, bismuth or combinations of at least two thereof, with phosphorus being particularly preferred. As described above, the various doping levels of the pn junction can be varied to tune the desired properties of the resulting solar cell. The degree of doping is measured using secondary ion mass spectrometry. According to some embodiments, the semiconductor substrate (ie, the germanium wafer) exhibits a sheet resistance of greater than about 60 Ω/□, such as greater than about 65 Ω/□, 70 Ω/□, 90 Ω/□, or 100 Ω/ □. To measure the sheet resistance of the doped wafer surface, a device "GP4-Test Pro" (available from GP Solar GmbH) equipped with a software kit "GP-4 Test 1.6.6 Pro" was used. For measurement, the four-point measurement principle is applied. Two external probes apply a constant current and two internal probes measure the voltage. The sheet resistance was derived in Ω/□ using Ohmic law. To determine the average sheet resistance, 25 equally distributed points of the wafer were measured. In an air-conditioned room at a temperature of 22 ± 1 ° C, balance all equipment and materials prior to measurement. For measurement, "GP-Test.Pro" is equipped with a 4-point measuring head (part number 04.01.0018) with a sharp tip to penetrate the anti-reflection and/or passivation layer. Apply 10 mA of current. The probe is brought into contact with the non-metallized wafer material and measurement begins. After measuring 25 equally distributed points on the wafer, the average sheet resistance is calculated in Ω/□. Solar Cell Structure The solar cell obtained according to the method of the present invention contributes to achieving at least one of the objects described above. The preferred solar cells of the present invention are solar cells and their lightweight and durable solar cells that have high efficiency in converting the total energy of incident light into a ratio of electrical energy output. At a minimum, the solar cell includes: (i) a front electrode, (ii) a positive doped layer, (iii) a pn junction boundary, (iv) a back doped layer, and (v) a solder pad. As explained herein, the solar cell can also include additional layers, particularly PERC solar cells. Antireflection Layer According to the present invention, an antireflection layer can be applied as an outer layer before the electrode is applied to the front side of the solar cell. In one embodiment, the anti-reflective layer can also be applied to the back surface of the solar cell. All antireflective layers known in the art and considered suitable in the context of the present invention may be employed. Preferred anti-reflective layers are anti-reflective layers that reduce the proportion of incident light that is reflected by the front side and increase the proportion of incident light that is absorbed through the front surface of the wafer. An antireflection layer that produces a favorable absorption/reflection ratio, is susceptible to etching by conductive paste, is otherwise resistant to the temperature required to burn the conductive paste, and does not increase the recombination of electrons and holes in the vicinity of the electrode interface is preferred. . Preferred antireflective layers include but are not limited to SiN x, SiO 2, Al 2 O 3, TiO 2 or a mixture of at least two compositions and / or at least two layers. According to a preferred embodiment, the anti-reflective layer is SiN x , in particular a germanium wafer is used. The thickness of the antireflective layer is adapted to the wavelength of the appropriate light. According to a preferred embodiment of the invention, the antireflection layer has a thickness of at least 20 nm, preferably at least 40 nm and most preferably at least 60 nm. At the same time, the thickness is preferably no more than about 300 nm, more preferably no more than about 200 nm and most preferably no more than about 90 nm. Passivation Layer One or more passivation layers can be applied as an outer layer to the front side and/or the back side of the germanium wafer. One or more positive passivation layers may be applied prior to formation of the front electrode or prior to application of the anti-reflective layer (if an anti-reflective layer is present). One or more backside passivation layers are typically applied during the production of the wafer, such as by plasma vapor deposition techniques. During the production of the PERC solar cell, a positive anti-reflective layer is first applied, followed by a backside passivation layer, and finally a back cover layer. Preferred passivation layers are passivation layers that reduce the electron/hole recombination rate near the electrode interface. Any passivation layer known in the art and considered suitable in the context of the present invention may be employed. Preferred passivation layers of the present invention include, but are not limited to, alumina (e.g., Al 2 O 3 ). The thickness of the passivation layer is preferably at least 0.1 nm, preferably at least 10 nm and most preferably at least 30 nm. At the same time, the thickness is preferably no more than about 2 μm, preferably no more than about 1 μm and most preferably no more than about 200 nm. Additional Protective Layer In addition to the above layers, additional layers may be added for mechanical and chemical protection. The battery can be packaged to provide chemical protection. According to a preferred embodiment, if such a package is present, a transparent polymer, often referred to as a transparent thermoplastic resin, is used as the encapsulating material. Preferred transparent polymers in this context are ruthenium rubber and polyvinyl acetate (PVA). A transparent glass sheet can also be added to the front side of the solar cell to provide mechanical protection to the front side of the battery. A back protection material can be added to the back of the solar cell to provide mechanical protection. Preferred back protection materials are those having good mechanical properties and weather resistance. A preferred back protective material of the present invention is polyethylene terephthalate having a polyvinyl fluoride layer. The back protective material preferably exists below the encapsulation layer (in the presence of both the back protection layer and the package). A frame material can be added to the outside of the solar cell to obtain mechanical support. The frame material is well known in the art and any frame material deemed suitable for use in the context of the present invention can be employed. A preferred frame material for the present invention is aluminum. PERC was prepared a solar cell of the solar cell was prepared by the PERC. First, a positive side diffusion layer as explained above is formed on the germanium substrate. On the positive side of the substrate, an anti-reflective coating, such as the anti-reflective coatings disclosed herein, is then applied. Subsequently, a back passivation layer such as an aluminum oxide layer is applied to the back surface of the substrate, such as by plasma vapor deposition. An additional backing layer, such as a tantalum nitride cap layer, can then be applied over the back passivation layer. Subsequently, a portion of the back passivation layer and an additional back layer are removed to expose the area of the underlying substrate. This step can be achieved by, for example, acid etching or laser drilling. An aluminum conductive paste is then applied over the backside layer, thereby filling the "holes" created by removing portions of the backside passivation layer. In these areas, a local back surface field is formed when the aluminum glue is burned. The back side solder tab can be applied to the back surface either before or after application of the aluminum glue. A positive side electrode having a backside solder tab is also formed according to conventional methods known in the art. An exemplary PERC solar cell is illustrated in FIG. In these figures, the term "AR" refers to the anti-reflective layer, the term "BSF" refers to the back surface field, the term "AlO x " refers to the backside passivation layer of alumina, and the term "SiN x " refers to the back cover. Layer, the term "back side Al" refers to the back side aluminum paste and the term "back side Ag" refers to the back side solder sheet. The conductive paste can be applied in any manner known in the art and deemed suitable in the context of the present invention. Examples include, but are not limited to, impregnation, dipping, pouring, dripping, injecting, spraying, knife coating, curtain coating, brushing or printing, or combinations of at least two thereof. Preferred printing techniques are ink jet printing, screen printing, mobile printing, lithography, letterpress or stencil printing, or a combination of at least two thereof. According to the invention, the positive and back side conductive pastes are preferably applied by printing, preferably by screen printing. In particular, the screen preferably has a mesh having a diameter of about 40 μm or less (e.g., about 35 μm or less, about 30 μm or less than 30 μm). At the same time, the screen preferably has a mesh having a diameter of at least 10 μm. The substrate is then subjected to one or more heat treatment steps such as, for example, conventional drying, infrared or ultraviolet curing and/or combustion. In one embodiment, the substrate can be burned according to an appropriate profile. Combustion sinters the printed conductive paste to form a solid electrode. Combustion is well known in the art and can be considered in any manner suitable for the context of the present invention. Preferably the combustion in the feed material greater than T g of the glass. According to the invention, the maximum temperature set for combustion is less than about 1000 ° C, preferably less than about 900 ° C. Furnaces with temperature settings as low as about 800 ° C have been employed for obtaining solar cells. The combustion temperature should also allow for effective sintering of the metal particles. The combustion temperature profile is typically set so that the organic material from the conductive paste composition can be burned out. The combustion step is usually carried out in air or in an oxygen-containing atmosphere in a belt furnace. The combustion is preferably carried out in a rapid combustion process with a total burn time of at least 30 seconds and preferably at least 40 seconds. At the same time, the burning time is preferably no more than about 3 minutes, more preferably no more than about 2 minutes and most preferably no more than about 1 minute. The time at which the wafer temperature is higher than 600 ° C is preferably in the range of about 3 seconds to 7 seconds. The substrate can reach a peak temperature in the range of about 700 to 975 ° C for a period of about 1 to 5 seconds. The combustion can also be carried out, for example, at a high transmission rate of about 100 to 700 cm/min, and the resulting residence time is about 0.5 to 3 minutes. Multiple temperature zones (eg, 3-12 zones) can be used to control the desired heat distribution. The burning of the front and back sides of the conductive paste can be carried out simultaneously or sequentially. If the conductive paste applied to both faces has similar, preferably identical, optimum combustion conditions, simultaneous combustion is appropriate. Where appropriate, the combustion is preferably carried out simultaneously. In the case of sequential combustion, it is preferred to first coat and burn the back conductive paste, and then coat and burn the conductive paste to the front side of the substrate. Measuring the properties of the conductive adhesive The electrical performance of the solar cell was measured using a commercial IV-tester "cetisPV-CTL1" from Halm Elektronik GmbH. During the power measurement, all components of the measuring device and the solar cells to be tested were kept at 25 °C. During the actual measurement, this temperature should be measured simultaneously on the surface of the battery by means of a temperature probe. The Xe arc lamp simulates daylight on the surface of the battery with a known AM 1.5 intensity of 1000 W/m 2 . In order for the simulator to reach this intensity, the lamp is flashed several times in a short period of time until it reaches the stability monitored by the "PVCTControl 4.313.0" software of the IV-tester. The Halm IV tester uses a multi-point contact method to measure current (I) and voltage (V) to determine the IV curve of the solar cell. To perform this process, the solar cells are placed between the multi-point contact probes in a manner such that the probe hands are in contact with the busbars (i.e., printed lines) of the solar cells. The number of contact probe wires is adjusted to the number of bus bars on the surface of the battery. All electrical values are automatically determined directly from the software package implemented by this curve. As a reference standard, calibrated solar cells from ISE Freiburg, which consisted of the same area dimension, the same wafer material and processed using the same positive side layout, were tested and compared to the pass values. At least five wafers processed in exactly the same manner are measured and the data is interpreted by calculating the average of the values. Software PVCTControl 4.313.0 provides values for efficiency (Eta), fill factor (FF), short circuit current (Jsc), series resistance (Rs), and open circuit voltage (Voc). Solar Cell Module A plurality of solar cells of the present invention can be spatially configured and electrically connected to form a collective configuration called a module. The preferred module of the present invention can have a plurality of configurations, preferably a rectangular configuration called a solar panel. A wide variety of ways to electrically connect solar cells, as well as a wide variety of mechanical configurations and ways of securing such cells to form a collective configuration are well known in the art. Preferred methods of the present invention are those which produce low mass to power output ratios, low volume to power output ratios, and high durability. Aluminum is a preferred material for mechanically fixing the solar cell of the present invention. In one embodiment, a plurality of solar cells are connected in series and/or in parallel and the electrode ends of the first and last cells are preferably connected to the output wires. The battery connector is joined to the area in which the back side solder tab has been formed. Solar cells are typically packaged in a clear thermoplastic resin such as silicone rubber or ethylene vinyl acetate. The transparent glass piece is placed on the front surface of the packaged transparent thermoplastic resin. A back protective material such as a polyethylene terephthalate sheet coated with a polyvinyl fluoride film is placed under the packaged thermoplastic resin. These layered materials can be heated in a suitable vacuum furnace to remove air and then integrated into a body by heating and pressing. Further, since the solar cell is usually placed in the open air for a long time, it is necessary to cover the periphery of the solar cell with a frame material composed of aluminum or the like. The invention will now be described in connection with the following non-limiting examples. Example 1 A first set of exemplary conductive paste compositions and a reference conductive paste composition were prepared according to the compositions set forth in Table 1 below. All values are provided as a percentage by weight based on 100% by total weight of the gum composition. The glass frit in each gum is from about 75.5 wt% (SiO 2 + B 2 O 3 + Bi 2 O 3 ), about 13 wt% of one or more alkali metal oxides, about 9.6, based on 100% by weight of the glass frit. Wt% ZnO and about 1.9 wt% Nb 2 O 5 are formed. Table 1. Exemplary gel formulations Each of the exemplary glue formulations is then printed on the back side of the PERC wafer to form a backside solder tab. In this example, a standard positive side glue (manufactured by Heraeus Precious Metals North America Conshohocken LLC of West Conshohocken, PA) was used using a screen with 280 mesh stainless steel wire at a wire diameter of about 35 μm and 5 μm EOM. SOL9621E) Screen printing onto the positive side of the PERC wafer to form the pointer lines and bus bars. The PERC wafers used were purchased from Sunrise Global Solar Energy Co., Ltd. (Wafer 1) in Yilan, Taiwan and SolarWorld Americas Inc. (Wafer 2) in Hillsboro, Oregon. The PERC wafer already has a partially open back passivation layer applied to its back side. For the latter case, the exemplary glue and reference glue of Example 1 were printed onto the back surface to form a backside solder tab that extends across the entire length of the cell and has a width of about 3.5 mm and a length of 1.53 mm. Next, a commercially available aluminum backside glue (RUX28K30 manufactured by Guangzhou Ruxing Technology Development Co., Ltd. of Guangdong, China) was printed on the back side of the wafer to form an aluminum back surface field in a partially open region of the back passivation layer and The back side solder tabs are slightly overlapped. The battery is then dried at the appropriate temperature. The tantalum substrate with the printed positive and back side gums is then burned at a peak temperature of about 700-975 °C. Electrical testing of each of the exemplary PERC solar cells is then performed in accordance with the parameters set forth herein. Electrical performance results are provided in Table 2 below. All data has been standardized relative to 100 based on reference gel data. As can be seen, both exemplary gel formulations exhibited improved open circuit voltage (Voc) compared to the reference gel composition. Therefore, regardless of the type of polyoxyxene used, it is shown that the presence of the improved electrical properties of the adhesive composition. Table 2. Exemplary electrical gum composition of efficacy Example 2 A second set of exemplary gels was prepared according to the compositions set forth in Table 3 below. All values are provided as a percentage by weight based on 100% by total weight of the gum composition. The glass frit of each of these gums is oxidized by about 82 wt% (SiO 2 + B 2 O 3 + Bi 2 O 3 ), about 10 wt% of one or more alkali metals, based on 100% by weight of the glass frit. Form, about 5 wt% ZnO, about 1 wt% Nb 2 O 5 and about 2 wt% MoO 3 are formed. Emu oil 2 is the same as that disclosed in Example 1. Table 3. Exemplary Glue Compositions Each of the exemplary gel formulations was then printed onto the back side of the PERC wafer and the electrical performance test was performed according to the parameters set forth in Example 1. In this example, the PERC wafers used were purchased from Jinko Solar Holding Co., Ltd., Shanghai, China. Electrical performance results are provided in Table 4 below. All data has been standardized relative to 100 based on reference gel data. As can be seen, all of the exemplary gel formulations exhibited improved efficiency (Eta, %) compared to the reference gel composition. Table 4 illustrates exemplary electrical gum composition of efficacy These and other advantages of the present invention will be apparent to those skilled in the art from this description. Thus, it will be appreciated by those skilled in the art that the invention may be modified or modified without departing from the scope of the invention. The specific dimensions of any particular embodiment are described for purposes of illustration only. Therefore, it is to be understood that the invention is not limited to the specific embodiments described herein, and all modifications and variations are intended to be included within the scope and spirit of the invention.