KR101691134B1 - Kesterite photo-absorber by Spatially tuned energy band gap - Google Patents
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Abstract
본 발명은 케스트라이트 Cu2ZnSnSe4 소재의 공간적인 에너지 밴드갭 변조방법에 의한 태양전지의 광흡수층 구조에 관한 것으로서, 케스트라이트 광흡수층에 경사를 갖는 전도밴드 구조를 만드는 방법에 관한 것이다. 이를 위해서, Sn 대신에 Ge을 일부 치환한 Cu2Zn(GexSn1-x)Se4 의 3층으로 구성된 광흡수층을 제작한다. Sn 대신에 Ge을 치환하게 되면 상기소재의 에너지 밴드갭이 증가된다. 광흡수층을 3층으로 나누어서 상층부와 하층부가 중간부보다 Ge의 치환량을 많게 만든다. 광흡수층의 상층부와 하층부를 비교하였을 경우에는 하층부에 Ge을 더 많이 치환하게 만들어서 에너지 밴드갭이 더 크게 만든다. 상기 구조로 제작된 광흡수층에는 광여기된 전자가 광흡수층의 상층부 위에 위치한 투명전극 쪽으로 잘 수집되며, 광전류 증가 효과를 얻을 수 있다. The present invention relates to a light absorption layer structure of a solar cell by a spatial energy bandgap modulation method of Kestlite Cu2ZnSnSe4 material, and relates to a method of making a conduction band structure having a slope in a Kestlite light absorption layer. For this purpose, a light absorbing layer composed of three layers of Cu2Zn (GexSn1-x) Se4 in which Ge is partially substituted for Sn is prepared. If the Ge is substituted for Sn, the energy band gap of the material is increased. The light absorption layer is divided into three layers so that the upper and lower layers make more Ge substitution than the middle portion. When the upper layer and the lower layer of the light absorbing layer are compared with each other, the energy band gap is made larger by substituting the Ge in the lower layer. In the light absorbing layer made of the above structure, the photoexcited electrons are collected well toward the transparent electrode located on the upper part of the light absorbing layer, and a photocurrent increasing effect can be obtained.
Description
본 발명은 태양전지 광흡수층으로 이용되는 케스트라이트 Cu2ZnSnSe4 소재의 에너지 밴드갭 변조방법에 의한 광흡수층 구조에 관한 것으로서, 더욱 상세하게는 Sn 대신에 Ge을 일부 치환하여서 밴드갭을 공간적으로 변조시키는 방법에 의한 태양전지의 광흡수층 구조에 관한 것이다.More particularly, the present invention relates to a method of spatially modulating a band gap by partially replacing Ge by a method of modulating an energy band gap of a Kestlite Cu2ZnSnSe4 material used as a solar cell light absorbing layer To a light absorbing layer structure of a solar cell.
케스트라이트 Cu2ZnSnS4 혹은 Cu2ZnSnSe4 소재는 태양전지의 광흡수층으로 이용되고 있다. Cu2ZnSnS4는 밴드갭이 1.4∼1.5 eV, Cu2ZnSnSe4는 밴드갭이 1∼1.1eV 값을 가지고 있다. 따라서 이 소재의 밴드갭 변조는 S와 Se의 성분조성에 따라서 밴드갭 이 조정된다. Cu2ZnSn(SxSe1 -x)4 에서 x의 값이 0에서 1로 증가되면, 밴드갭의 크기도 ∼1 eV에서 ∼1.5 eV로 증가된다. 이상적인 태양전지의 광흡수층 밴드갭은 1.3∼1.5 eV가 적당하지만, 상기 케스트라이트 태양전지의 경우는 S가 일부 Se으로 치환된 광흡수층을 사용할 경우 최고의 효율을 보이고 있다.(Device Characteristics of CZTSSe Thin-Film Solar Cells with 12.6% Efficiency, Wang et al, Adv. Energy Mater., 2014, 4, 1301465 )Light cast Cu 2 ZnSnS 4 or Cu 2 ZnSnSe4 materials have been used as a light absorbing layer of the solar cell. Cu2ZnSnS4 has a band gap of 1.4 to 1.5 eV, and Cu2ZnSnSe4 has a band gap of 1 to 1.1 eV. Therefore, the band gap modulation of this material is adjusted depending on the composition of S and Se. When the Cu2ZnSn (S x Se 1 -x) 4 value of x is increased from 0 to 1, the size of the band gap also increased in ~1 eV to ~1.5 eV. Ideally, the band gap of the light absorbing layer of the solar cell is suitably in the range of 1.3 to 1.5 eV. However, in the case of the Kestlite solar cell, when the light absorbing layer in which S is partially substituted with Se is used, Device efficiency of CZTSSe Thin- Film Solar Cells with 12.6% Efficiency, Wang et al, Adv. Energy Mater., 2014, 4, 1301465)
한편, 태양전지의 효율을 높이는 다른 기술로는 광흡수층의 에너지 밴드갭을 변조하는 기술이 Cu(In,Ga)Se2 태양전지에서 연구되고 있다. 도 1의 광흡수층은 밴드갭의 크기가 깊이 별로 다른 값을 가진다. 그 크기는 Eg3>Eg1>Eg2의 크기 순서로 만들어져서 광여기된 전자가 윈도우층에 잘 도달할 수 있게 만들어졌다(Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films, A. Chirila et al., Nature Materials 10, 857-861 (2011)). 이것은 광전류의 증가를 가능하게 해서 궁극적으로 광전변환 효율을 증가시킬 수 있다. 이런 목적을 위해서는 광흡수층의 공간적 밴드갭을 변조시키는 기술이 필요하다. 발표된 논문의 에너지 밴드갭 변조는 In에 대한 Ga의 치환량을 통해서 가능하다. Ga의 치환량이 Eg3 부분이 제일 많고, Eg1 및 Eg2 순서로 많이 치환되게 만들면, 상기의 에너지 갭 순서를 따르게 된다. On the other hand, as another technique for increasing the efficiency of a solar cell, a technique for modulating the energy band gap of the light absorption layer is studied in a Cu (In, Ga) Se 2 solar cell. In the light absorbing layer of FIG. 1, the band gap has a different value depending on the depth. Its size is Eg3>Eg1> Eg2 is created and the order of the light excited electrons is made able to better reach the window layer (Highly efficient Cu (In, Ga ) Se 2 solar cells grown on flexible polymer films, A. Chirila et al., Nature Materials 10, 857-861 (2011)). This makes it possible to increase the photocurrent and ultimately increase the photoelectric conversion efficiency. For this purpose, a technique for modulating the spatial band gap of the light absorbing layer is required. The energy bandgap modulation of the published paper is possible through the substitution of Ga for In. When the substitution amount of Ga is the largest in the Eg 3 portion and is made to be largely substituted in the order of
케스트라이트의 태양전지의 경우는 Sn에 대한 Ge의 치환량의 조절을 통해서 밴드갭 변조가 가능하다. Cu2ZnSnSe4에 Ge이 Sn 대신에 치환될 경우 에너지 밴드갭이 커지고, 이로 인해서 태양전지의 개방전압(open circuit voltage: Voc)이 커져서 광전변환 효율이 증가됨이 보고되었다(Hydrazine-Processed Ge-Substituted CZTSe Solar Cells, S. Bag, O. Gunawan, T. Gokmen, Y. Zhu, and D. B. Mitzi, Chemistry Materials 24(23) 4588-4593, 2012). Bag 등의 연구에서는 광흡수층을 공간적으로 그 성분을 변조하지 않고, 광흡수층을 Cu2ZnSnSe4 대신에, Cu2ZnSn0.6Ge0.4Se4을 사용하였다. In the case of Kestlite's solar cell, bandgap modulation is possible by adjusting the amount of Ge substitution on Sn. It has been reported that when Ge is substituted for Sn in Cu 2
한편, Cu2Zn(Sn1 - xGex)S4 소재에서 Ge의 치환량 x를 변조함으로써 공간적으로 광흡수층의 전도밴드가 단일 경사를 지게 만드는 연구가 보고되었다(Bandgap Graded Cu2Zn(Sn1 - xGex)S4 Thin Film Solar Cells Derived from Metal Chalcogenide Complex Ligand Capped Nanocrystals, Inhyuk Kim et al., Chemistry of Materials, 26(13), p3957-3965). 보고된 연구에서는 버퍼층 부분에 비해 바탕 전극층 부분쪽에 Ge을 많이 치환하여 광흡수층의 전도 밴드를 경사지게 만들었다. 이를 통해 광여기된 전자가 버퍼층 쪽으로 잘 전달되게 고안되었다. 하지만, 황화물 기반 광흡수층이 이용되었기 때문에, 버퍼층 CdS 부근의 광흡수층은 밴드갭이 1.62 eV, 바탕전극층 부근의 밴드갭은 1.84eV를 나타내었다. 이 밴드갭들은 태양광 스펙트럼을 이상적으로 흡수하기 하기 위한 밴드갭 크기 1.2∼1.4 eV보다 큰 값이어서 고효율 태양전지로 이용되기에 한계가 있다. On the other hand, it has been reported that modulating the substitution amount x of Ge in the Cu 2 Zn (Sn 1 - x Ge x ) S 4 material makes the conduction band of the light absorption layer spatially uniform by modulating the substitution amount x of the Cu 2 Zn (Sn 1 - - x Ge x ) S 4 Thin Film Solar Cells Derived from Metal Chalcogenide Complex Ligand Capped Nanocrystals, Inhyuk Kim et al., Chemistry of Materials, 26 (13), p3957-3965). In the reported study, the conduction band of the light absorbing layer was made to be inclined by substituting a lot of Ge in the part of the background electrode layer in comparison with the buffer layer part. The photoexcited electrons are designed to transfer to the buffer layer. However, since a sulfide-based light absorption layer was used, the band gap of the light absorption layer near the buffer layer CdS was 1.62 eV, and the band gap near the background electrode layer was 1.84 eV. These bandgaps are larger than the bandgap sizes of 1.2 to 1.4 eV for ideally absorbing the solar spectrum, and thus they are limited to be used as high-efficiency solar cells.
따라서, 광흡수층 변조를 위해서 셀레늄 기반 광흡수층 제조 방법이 요구된다. 즉, Cu2Zn(Sn1-xGex)Se4 소재에서 Sn의 치환량 x를 변조함으로서 광흡수층의 밴드갭 변조 방법을 제안한다. 이 경우 Ge의 치환량에 따라서 밴드갭이 1 eV에서 ∼1.5 eV까지 변조가 가능하다.Therefore, a method for manufacturing a selenium-based light absorbing layer for modulating the light absorption layer is required. That is, a band gap modulation method of a light absorption layer is proposed by modifying the substitution amount x of Sn in Cu2Zn (Sn1-xGex) Se4 material. In this case, it is possible to modulate the band gap from 1 eV to ~ 1.5 eV according to the substitution amount of Ge.
본 발명은 케스터라이트 태양전지의 광흡수층의 공간적 에너지 밴드갭 변조방법에 의한 상기 광흡수층 구조에 관한 것으로서 경사 전도 밴드를 갖는 태양전지의 광흡수층 제조를 목적으로 한다.The present invention relates to a light absorption layer structure by a spatial energy bandgap modulation method of a light absorption layer of a kesterlight solar cell, and aims at manufacturing a light absorption layer of a solar cell having an inclined conduction band.
케스트라이트 태양전지의 광수층은 도면 1에서 보이듯이 Eg3>Eg1>Eg2 순서의 크기로 제조되어서 광흡수층의 전도밴드가 이중 경사를 가지게 한다. The light-receiving layer of the Kestlite solar cell is fabricated in the order of Eg3> Eg1> Eg2, as shown in FIG. 1, so that the conduction band of the light absorption layer has a double inclination.
이와 같은 목적을 위해서 Cu2Zn(Sn1 - xGex)Se4 광흡수층에서 Ge을 Sn 대신에 치환하여서 광흡수층 밴드갭을 공간적으로 조정한다. Ge의 치환에 따라서 밴드갭이 1 eV에서 ∼1.4 eV까지 변조가 가능하다. 도 2에서와 같이 광흡수층을 Ge이 치환된 양에 따라 3개의 영역으로 나누어서 Region III에 Ge 치환량을 최대로 하고, Region I에 Ge 치환량을 중간으로 하며, Region II에 Ge 치환량을 최소로 해서 광흡수층을 구성한다.For this purpose, the band gap of the light absorption layer is spatially adjusted by substituting Ge for Sn in the Cu 2 Zn (Sn 1 - x Ge x ) Se 4 light absorption layer. According to the substitution of Ge, it is possible to modulate the band gap from 1 eV to ~ 1.4 eV. As shown in FIG. 2, the photoabsorption layer is divided into three regions according to the amount of Ge substitution to maximize Ge substitution in Region III, moderate Ge substitution in Region I, minimize Ge substitution in Region II Thereby constituting an absorbent layer.
Region III에 Ge 치환량을 최대로 하고, Region I에 Ge 치환량을 중간으로 하며, Region II에 Ge 치환량을 최소로 해서 광흡수층을 구성하면, 광수층은 도 1에서 보이듯이 Eg3>Eg1>Eg2 순서의 크기로 제조된다. 광흡수층의 전도밴드가 도 2와 같이 이중 경사를 가지면, Eg3가 크기 때문에 광여기된 전자는 윈도우층으로 효과적으로 전달된다. 한편, Eg1>Eg2이기 때문에 버퍼층 쪽의 밴드갭 Eg1이 다소 커지면 개방전압(Voc)이 커져서 광전 변환 효율이 커진다. 따라서 광흡수층의 전도밴드를 이중 경사를 가지게 해서 고효율 케스트라이트 태양전지 제조를 기대할 수 있는 효과가 있다.If the photoabsorption layer is made up to the maximum Ge substitution in Region III, the Ge substitution in Region I is the middle, and the Ge substitution in region II is the minimum, then the optical water layer will have the order Eg3> Eg1> Eg2 Size. When the conduction band of the light absorbing layer has a double tilt as shown in Fig. 2, the excited electrons are effectively transmitted to the window layer because Eg3 is large. On the other hand, since Eg1> Eg2, if the band gap Eg1 on the side of the buffer layer is somewhat larger, the open-circuit voltage Voc becomes larger and the photoelectric conversion efficiency becomes larger. Accordingly, the conduction band of the light absorbing layer has a double inclination, so that a highly efficient cast light solar cell can be expected to be manufactured.
도 1은 본 발명에 따른 광흡수층의 에너지 밴드 다이아그램. 전도밴드가 이중 경사를 가진다.
도 2는 본 발명에 따른 이중경사를 가진 광흡수층이 적용된 태양전지 다이아그램.
도 3은 본 발명에 따른 단일경사를 가진 광흡수층이 적용된 태양전지 다이아그램.
도 4는 Ge의 치환량 x를 0=x=1 로 변화시켜서 만든 Cu2Zn(Sn1 - xGex)Se4 박막의 UV-Visible spectroscopy 측정결과.
도 5는 Ge의 치환량 x를 0=x=1로 변화시켜서 만든 Cu2Zn(Sn1 - xGex)Se4 박막의 Raman spectroscopy 측정결과
도 6은 Ge의 치환량 x를 0=x=1로 변화시켜서 만든 Cu2Zn(Sn1 - xGex)Se4 박막의 X-ray diffraction 측정결과
도 7은 Ge의 치환량 x=0.3, 0.5, 0.7로 해서 만든 Cu2Zn(Sn1 - xGex)Se4 박막의 표면 주사전자현미경(SEM) 이미지1 is an energy band diagram of a light absorbing layer according to the present invention. The conduction band has double inclination.
2 is a photovoltaic cell diagram to which a light absorption layer having a double inclination according to the present invention is applied.
FIG. 3 is a photovoltaic cell diagram to which a light absorption layer having a single inclination according to the present invention is applied.
Figure 4 is the substitution amount x of
5 shows Raman spectroscopy results of Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin films prepared by changing the substitution amount x of Ge to 0 = x = 1
Figure 6 is the substitution amount x 0 = x = 2 made by changing a
FIG. 7 is a scanning electron microscope (SEM) image of a Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin film made of Ge substitution x = 0.3, 0.5,
이하에서는, 본 발명의 바람직한 실시예를 첨부한 도 2 내지 6을 참조하여 상세하게 설명하기로 한다. 본 실시예는 당해 발명에 속하는 기술분야에서 통상의 지식을 가진 자가 본 발명을 용이하게 실시할 수 있을 정도로 상세하게 설명하기 위한 것이지, 이로써 본 발명의 사상 및 범주가 한정되는 것을 의미하지는 않는다.Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 2 to 6 attached hereto. The present embodiments are intended to illustrate the present invention in a manner that allows a person skilled in the pertinent art to easily carry out the present invention, and thus the spirit and scope of the present invention are not limited thereto.
도 2는 본 발명에 따른 광흡수층의 이중 경사를 가진 광흡수층이 적용된 태양전지를 보여준다. 광흡수층의 Region I, Region II, Region III의 Ge 치환량 x, y, z를 다르게 함으로써 3층의 에너지 밴드갭을 다르게 구현한다. x, y, z의 크기는 z>x>y 의 크기로 해서 에너지 밴드갭이 Region III > Region I > Region II 로 구현한다. 이렇게 구현된 광흡수층은 도 1의 에너지 밴드 다이아그램을 갖는다. FIG. 2 shows a solar cell to which a light absorption layer having a double inclination of the light absorption layer according to the present invention is applied. By varying the Ge substitution x, y, z of Region I, Region II, and Region III of the light absorption layer, the energy bandgap of the three layers is differently implemented. The size of x, y, and z is the size of z> x> y and the energy bandgap is implemented as Region III> Region I> Region II. The light absorbing layer thus implemented has the energy band diagram of Fig.
한편, Region I 과 Region III 의 두께를 조정하고, Region I, Region II, Region III의 Ge 치환량의 차이가 적게 되면 도 3과 같은 단일 경사의 에너지 밴드가 구현될 수 있다.On the other hand, if the thicknesses of Region I and Region III are adjusted and the difference in Ge substitution between regions I, II, and III is small, a single inclined energy band as shown in FIG. 3 can be realized.
도 4는 Ge의 치환량 x 를 0 ≤ x ≤ 1로 변화시켜서 만든 Cu2Zn(Sn1 - xGex)Se4 박막의 UV-Visible spectroscopy 측정결과로 각 그래프의 접선의 x 축 절편이 에너지 밴드갭을 나타낸다. X가 0에서 1로 변할 경우 그 크기가 ∼1 eV에서 ∼1.5 eV로 커짐을 보여준다. 이 결과는 스프레이 기반으로 만든 시료의 실험 결과이다. Figure 4 is the substitution amount x of 0 ≤ x ≤ made by changing to 1 Cu 2 Zn of Ge (Sn 1 - x Ge x) Se 4 UV-Visible spectroscopy the x-axis intercept of the tangent of each graph with measurement results of energy band of a thin film Lt; / RTI > When X changes from 0 to 1, its size increases from ~ 1 eV to ~ 1.5 eV. This result is an experimental result of a spray-based sample.
도 5는 Ge의 치환량 x를 0 ≤ x ≤ 1로 변화시켜서 만든 Cu2Zn(Sn1 - xGex)Se4 박막의 Raman spectroscopy 측정결과로 x가 0에서 1로 변할 경우 Raman A1 mode peak 위치가 ~194 cm- 1 에서 ~204 cm-1로 점차적으로 이동됨을 보여준다. 이 결과는 Sn 보다 Ge이 무겁기 때문에 phonon vibration frequency가 Ge이 치환됨에 따라 커짐을 의미한다. 여기서 Raman spectrum 의 패턴과 peak의 반치폭이 크게 변하지 않음을 알 수 있고, 이는 Ge이 치환되어도 그 Cu2Zn(Sn1 - xGex)Se4 박막의 결정성이 크게 나빠지지 않음을 의미한다. 이 결과는 스프레이 기반으로 만든 시료의 실험 결과이다.5 is Ge substitution amount x to create varied as 0 ≤ x ≤ 1 Cu 2 Zn of - if the Raman spectroscopy measurements of the (Sn 1 x Ge x) Se 4 thin-film x is changed to 1 0 Raman A1 mode peak position the ~ 194 cm - 204 cm -1 at one to ~ shows that gradually moved. This result implies that the phonon vibration frequency increases with the substitution of Ge because Ge is heavier than Sn. It can be seen that the half width of the pattern and peak of the Raman spectrum are not largely changed. This means that the crystallinity of the Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin film is not deteriorated even if Ge is substituted. This result is an experimental result of a spray-based sample.
도 6은 Ge의 치환량 x를 0 ≤ x ≤ 1로 변화시켜서 만든 Cu2Zn(Sn1 - xGex)Se4 박막의 X선 회절(XRD) 측정결과로 x가 0에서 1로 변할 경우 XRD peak 위치가 더 큰 2theta 값을 갖는 쪽으로 변하고 있다. 이는 Sn 보다 Ge이 사이즈가 더 크기 때문에 결정의 격자상수가 Ge이 치환됨에 따라 커짐을 의미한다. 여기서 XRD peak의 반치폭이 크게 변하지 않음을 알 수 있고, 이는 Ge이 치환되어도 그 결정성이 크게 나빠지지 않음을 의미한다. 이 결과는 스프레이 기반으로 만든 시료의 실험 결과이다.6 shows XRD results of Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin films formed by changing the substitution amount x of Ge to 0 ≦ x ≦ 1, and when X changes from 0 to 1, XRD the peak position is shifting toward a larger 2theta value. This means that the crystal lattice constant increases with the substitution of Ge because the size of Ge is larger than that of Sn. Here, it can be seen that the half width of the XRD peak is not largely changed, which means that even if Ge is substituted, the crystallinity thereof does not deteriorate greatly. This result is an experimental result of a spray-based sample.
도 7 은 Ge의 치환량 x = 0.3, 0.5, 0.7로 해서 만든 Cu2Zn(Sn1 - xGex)Se4 박막의 표면 주사전자현미경(SEM) 이미지로서 모든 박막이 비교적 큰 grain을 가진 다결정 구조로 잘 성장하였음을 보여준다. 이는 Ge이 치환되어도 결정성이 좋은 Cu2Zn(Sn1-xGex)Se4 박막이 성장됨을 보여준다. 이 결과는 스프레이 기반으로 만든 시료의 실험 결과이다.7 is a scanning electron microscope (SEM) image of a Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin film made of Ge substitution x = 0.3, 0.5 and 0.7, wherein all thin films have a relatively large grained polycrystalline structure As well. This shows that Cu 2 Zn (Sn 1-x Ge x ) Se 4 thin film having good crystallinity is grown even when Ge is substituted. This result is an experimental result of a spray-based sample.
도 4는 밴드갭 크기도 Ge의 치환량 x에 따라 임의로 조정할 수 있음을 보여준다. 따라서 Ge이 치환된 Cu2Zn(Sn1 - xGex)Se4 박막을 이용해서 도 1과 도 2의 에너지 밴드갭이 변조된 광흡수층을 용이하게 구현할 수 있음을 알 수 있다. 예를 들어서 도 4의 결과에 의하면 Region Ⅰ을 x=0.5인 Cu2Zn(Sn1 - xGex)Se4 박막을 만들고, Region II를 x=0, Region III을 x=0.3인 Cu2Zn(Sn1 - xGex)Se4 박막으로 만들면 Eg1=1.262 eV, Eg2=1.074 eV, Eg3=1.181 eV인 가운데 부분의 밴드갭이 가장 작은 이중 경사를 가진 광흡수층을 구현할 수 있다. 도 5 내지 도 7의 결과는 Ge의 치환량 x를 0=x=1로 변화시켜서 만든 Cu2Zn(Sn1 - xGex)Se4 박막을 만들 경우 박막의 결정성이 나빠지지 않고 잘 제조할 수 있음을 의미한다.FIG. 4 shows that the band gap size can be arbitrarily adjusted according to the substitution amount x of Ge. Therefore, it can be seen that the optical absorption layer with the energy band gap modulated in FIGS. 1 and 2 can be easily implemented using the Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin film substituted with Ge. For example, according to the results shown in FIG. 4, a Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin film having x = 0.5 is formed in Region I, a Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin film, it is possible to realize a light absorbing layer having a double slope having the smallest bandgap in the center portion, Eg1 = 1.262 eV, Eg2 = 1.074 eV and Eg3 = 1.181 eV. 5 to 7 show that when a Cu 2 Zn (Sn 1 - x Ge x ) Se 4 thin film formed by changing the substitution amount x of Ge to 0 = x = 1 is formed, the crystallinity of the thin film is not deteriorated, .
이와 같이 본 발명은 공간적 에너지 밴드갭 변조방법에 의해 다층 구조의 Cu2Zn(Sn1-xGex)(Se1-mSm)4로 된 태양전지의 광흡수층을 갖는데, 이 중 3층 구조의 광흡수층의 경우 상기 광흡수층의 상층부는 Cu2Zn(Sn1-xGex)(Se1-mSm)4, 중간부는 Cu2Zn(Sn1-yGey)(Se1-mSm)4, 하층부는 Cu2Zn(Sn1-zGez)(Se1-mSm)4로 구성하며 y<x<z(여기서 x는 0 < x < 1, y는 0 < y < 1, z는 0 < z ≤ 1 임)로 구성한다.As described above, the present invention has a light absorbing layer of a solar cell made of Cu 2 Zn (Sn 1-x Ge x ) (Se 1-m S m ) 4 of a multi-layer structure by a spatial energy band gap modulation method, for the structure of the upper light absorbing layer of the light absorbing layer is Cu 2 Zn (Sn 1-x Ge x) (Se 1-m S m) 4, The middle part consists of Cu 2 Zn (Sn 1-y Ge y) (Se 1-m S m) 4, lower layer is Cu 2 Zn (Sn 1-z Ge z) (Se 1-m S m) 4 , and y < x <z, where x is 0 <x <1, y is 0 <y <1, and z is 0 <z ≤ 1.
또한 상기 광흡수층의 상층부는 Cu2Zn(Sn1 - xGex)(Se1 - mSm)4, 중간부는 Cu2Zn(Sn1 -yGey)(Se1-mSm)4, 하층부는 Cu2Zn(Sn1 - zGez)(Se1 - mSm)4로 구성하며 x=y=z(여기서 x, y, z는 0<x,y,z≤1 임)로 구성한다. 이 경우 광흡수층은 단순히 Ge이 전체적으로 균일하게 치환된 단일층과 같으며, 광흡수층의 전도밴드는 경사를 가지지 않는다. 단 Ge의 도핑으로 광흡수층의 에너지 밴드갭이 커지는 효과가 기대된다.The upper part of the light absorption layer is composed of Cu 2 Zn (Sn 1 - x Ge x ) (Se 1 - m S m ) 4 , Intermediate portions Cu 2 Zn (Sn 1 -y Ge y) (Se 1-m S m) 4, lower layer is Cu 2 Zn (Sn 1 - z Ge z) - consists of (Se 1 m S m) 4, and x = y = z where x, y, z are 0 < x, y, z < In this case, the light absorbing layer is simply a single layer in which Ge is uniformly substituted as a whole, and the conduction band of the light absorbing layer does not have a slope. However, the effect of increasing the energy band gap of the light absorption layer by doping with Ge is expected.
한편 상기 광흡수층의 상층부, 중간부, 하층부의 두께는 임의의 두께 값을 가질 수 있도록 하되, 상기 상층부, 중간부, 하층부로 이루어진 광흡수층의 총 두께는 100nm 에서 10,000nm 사이의 값을 갖는 것이 바람직하며, Cu2Zn(Sn1-xGex)(Se1-mSm)4로 된 광흡수층의 다층 구조에서 m은 0<m≤0.95로 구성하는 것이 바람직하다.Meanwhile, it is preferable that the thickness of the upper layer portion, the middle portion and the lower layer portion of the light absorbing layer has an arbitrary thickness value, and the total thickness of the light absorbing layer composed of the upper layer portion, the middle portion and the lower layer portion has a value between 100 nm and 10,000 nm , And m in the multilayer structure of the light absorption layer made of Cu 2 Zn (Sn 1-x Ge x ) (Se 1-m S m ) 4 is preferably 0 <m ≦ 0.95.
10 : 광흡수층의 valence band maximum
20 : 광흡수층의 conduction band minimum
30 : 광흡수에 의해 생긴 광 전자(electron)10: valence band maximum of the light absorption layer
20: Conduction band minimum of the light absorbing layer
30: photoelectron generated by light absorption
Claims (6)
상기 광흡수층의 상층부, 중간부, 하층부의 두께는 임의의 두께 값을 가질 수 있도록 하되, 상기 상층부, 중간부, 하층부로 이루어진 광흡수층의 총 두께는 100nm 에서 10,000nm 사이의 값을 갖는 것을 특징으로 하는 공간적 에너지 밴드갭 변조방법에 의한 태양전지의 광흡수층 구조.The method according to claim 1 or 4,
The total thickness of the light absorbing layer composed of the upper layer portion, the middle portion and the lower layer portion has a value between 100 nm and 10,000 nm so that the thickness of the upper layer portion, middle portion and lower layer portion of the light absorbing layer can have an arbitrary thickness value. Structure of Photovoltaic Cells by Spatial Energy Bandgap Modulation.
m은 0.1<m≤0.95로 구성한 것을 특징으로 하는 공간적 에너지 밴드갭 변조방법에 의한 태양전지의 광흡수층 구조.The method according to claim 1 or 4,
m is 0.1 < m < = 0.95.
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