TWI401812B - Solar battery - Google Patents

Description

Solar battery

The present invention relates to a solar cell, and more particularly to an amorphous germanium solar cell.

The spectrum of solar radiation is mainly centered on visible light, and its distribution range is from 0.3 micrometer (μm) ultraviolet light to several micrometers of infrared light. If converted into photon energy, it is about 0.4eV (electron volt). Between 4eV. In general, an ideal solar cell material must have the following characteristics: an energy gap between 1.1 eV and 1.7 eV, a direct energy gap semiconductor, a non-toxic material, a thin film deposition technique, and a large-area fabrication. It has good photoelectric conversion efficiency and long-term stability. The energy gap of germanium is 1.12eV, and it is an indirect energy gap semiconductor. It has poor absorption of light, so it is not the best in this respect. The material, but it is the second most abundant element on the earth, and the ruthenium itself is non-toxic, its oxide is stable and not water-soluble, so the current solar cells still use bismuth as the main material.

According to different crystallization modes, germanium atoms can be divided into single crystal germanium, polycrystalline germanium and amorphous germanium. Solar cells made of single crystal germanium are highly efficient and stable in performance, and have been widely used in space and on land; polycrystalline germanium There are more than one kind of atomic packing method. It is composed of a single crystal in a variety of different orientations. Because of its simple process and low cost, the solar cell production produced by polycrystalline germanium has gradually surpassed that of single crystal germanium. Amorphous germanium means that the arrangement of germanium atoms is very disordered and there are no rules to follow. Generally, the amorphous germanium is an amorphous germanium film having a thickness of about 1 micrometer (μm) grown on a substrate such as glass by a Plasma Enhanced Chemical Vapor Deposition (PECVD) because of the amorphous germanium pair. The absorption of light is about 500 times stronger than that of bare, so only a thin layer is needed for the amorphous germanium to absorb the energy of the photon, and it is not necessary to use an expensive crystalline germanium substrate, and the price is cheaper. The glass, ceramic or metal substrate can not only save a lot of material costs, but also make it possible to make a large area of solar cells.

Referring to FIG. 1, a general amorphous germanium solar cell structure includes a substrate 11, an amorphous germanium film 12 deposited on the substrate 11, and a top electrode 13 in ohmic contact with the amorphous germanium film 12.

The substrate 11 has a substrate 111 made of glass, and a transparent conductive film 112 formed on the surface of the substrate 111 and made of indium tin oxide (ITO). The amorphous germanium film 12 is formed on the transparent conductive film 112. And ohmic contact with the transparent conductive film 112, the electric energy can be generated by the photovoltaic effect when the light is irradiated, the top electrode 13 is formed on the amorphous germanium film 12, and the transparent conductive film 112 can cooperate with the amorphous germanium film. 12 The generated electric energy is output to the outside.

The amorphous germanium film 12 has a positive-type semiconductor 123 and a negative-type semiconductor 125 having a step difference by doping, and an energy level is located in the P and N types. An intrinsic semiconductor 124 between the energy levels of the semiconductors 123, 125, when the amorphous germanium thin film solar cell is illuminated, the P-type semiconductor 123, the pure semiconductor 124, and the N-type semiconductor 125 absorb photons to generate electrons - In the pair of holes, the electron-hole pair forms a photocurrent due to the separation of the built-in power, and the top electrode 13 and the transparent conductive film 112 cooperate to output the generated photocurrent to the outside.

However, the production ratio of amorphous germanium solar cells has gradually declined in recent years, and the main factor affecting the development of amorphous germanium solar cells is the stability problem. Since amorphous germanium materials contain a large number of defects and unbonded Dangling Bonds, under intense light irradiation, defects will occur and current drops (the so-called Staebler-Wronski effect) occur. The problem of unstable power supply, and with the increase of illumination time, the efficiency of amorphous silicon solar cells will also decay rapidly. Although dual-junction (a-Si/a-SiGe) batteries are currently used to improve the stability of amorphous tantalum thin film solar cells, there is still room for continuous development.

Therefore, how to develop the disadvantages of reducing the instability of the amorphous germanium film and the material suitable for the energy gap of the solar cell to improve the stability and light utilization efficiency of the amorphous germanium solar cell has been an important goal of the continuous efforts of the solar energy technology field. .

Accordingly, it is an object of the present invention to provide an amorphous germanium solar cell having high stability and high light utilization efficiency.

Thus, a solar cell of the present invention comprises a substrate, an amorphous germanium film, and a top electrode.

The substrate is electrically conductive.

The amorphous germanium film is formed on the transparent conductive film and is in ohmic contact with the substrate, and includes a P-type semiconductor doped with energy level difference, an N-type semiconductor, and an energy level located in the P, N-type semiconductor An intrinsic semiconductor between the energy levels, the intrinsic semiconductor having a crystalline region and an amorphous region, the proportion of the crystalline region being 25 to 45% of the intrinsic semiconductor, the grain size being no greater than 30 nm, and located at 2070 to 2100 cm The Si-H bonding strength of ^-1 accounts for 35-60% of the crystalline region, and the amorphous germanium film with nanocrystalline crystal can convert light energy into electrical energy by the photovoltaic effect when receiving solar energy.

The top electrode is formed on the amorphous germanium film, and the substrate can cooperate with the substrate to output the electrical energy generated by the amorphous germanium film to the outside.

The effect of the invention is that the crystallinity is between 25 and 45%, and the grain size of the crystallized state is controlled to be no more than 30 nm, and the Si-H bonding strength at 2070 to 2100 cm ^-1 is occupied by the crystal. 35 to 60% of the intrinsic semiconductors in the region can not only reduce the problem of the efficiency of the amorphous silicon solar cell after illumination, but also form a multi-gap structure to increase the light absorption capacity of different wavelengths, and increase the photocurrent of the output. .

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Referring to FIG. 2, the preferred embodiment of the solar cell of the present invention is similar in structure to the conventional amorphous germanium solar cell, and comprises a substrate 2, an amorphous germanium film 3, and a top electrode 4.

The substrate 2 has a substrate 21 and a transparent conductive film 22 formed on the surface of the substrate 21. The substrate and the related processes and materials of the transparent conductive film 22 are well known in the art. It is not the focus of the present invention, so the description is not repeated. In the preferred embodiment, the substrate 21 is glass, and the transparent conductive film 22 is made of zinc oxide containing doped carriers. The transmittance between 50 and 800 nm and the surface roughness of 5 to 25 nm in visible light is more than 85% and the sheet resistance is between 5 Ω/□ and 15 Ω/□.

It is worth mentioning that when the doping carrier concentration of the transparent conductive film 22 is insufficient or the carrier mobility is too low, the conductivity is poor and the output efficiency is affected. Therefore, preferably, the doping is performed. The zinc oxide has a doping carrier concentration of 1×10 ¹⁹ to 4×10 ²⁰ cm ⁻³ , a crystal size of 5 to 15 nm, and a carrier mobility of 5 to 250 cm ² /Vs.

Referring to Table 1, Table 1 shows conductive films having different carrier concentrations, carrier mobility, crystal size, and sheet resistance values at different ratios of O ₂ :Ar process gases.

The amorphous germanium film 3 is formed on the transparent conductive film 22 with a surface roughness of 2 to 15 nm and is in ohmic contact with the transparent conductive film 22, and converts light energy into a photovoltaic effect when receiving solar energy. The electric energy includes a P-type semiconductor 31 doped with an energy level difference, an N-type semiconductor 33, and an intrinsic semiconductor 32 having an energy level between the energy levels of the P, N-type semiconductors 31, 33.

In particular, the intrinsic semiconductor 32 has a crystalline region and an amorphous region, and the ratio of the crystalline region is 25 to 65% of the intrinsic semiconductor, that is, the crystallinity of the intrinsic semiconductor 32 is 25 to 65%, and the crystal The particle size is not more than 30 nm.

It should be noted that since the crystalline form of the crystalline region of the intrinsic semiconductor has a great influence on the energy gap and efficiency of the intrinsic semiconductor 32, the more dense the crystal in the crystalline region and the less the defects, the better the quantum efficiency. From the analysis of Si-H bond FT-IR, it is known that the Si-H bond with a relatively dense crystallinity has a strong absorption between 2070 and 2100 cm ^-1 and a peak occurs. Therefore, preferably, the essence The Si-H bonding strength of the semiconductor 32 at 2070-2100 cm ^-1 is between 35 and 60% of the crystallization region.

In particular, when the crystal grain of the nanocrystalline crystal is less than 30 nm, a quantum confinement effect can be formed, and the change of the energy gap can be adjusted by the size, and when the electron is affected by the quantum confinement effect, the original continuous band structure becomes The energy level structure of the split, which in turn causes the original indirect energy gap of the crucible to become an energy band structure close to the direct energy gap. In addition, the quantum confinement effect can improve the electrical characteristics to increase the range of absorbable incident light energy spectrum, but when the proportion of the crystallization region is greater than 50%, the leakage current of the intrinsic semiconductor 32 will increase; When the ratio of the crystallization zone is too small, the carrier mobility will also decrease. Therefore, preferably, the ratio of the crystallization zone is between 25% and 50%, and more preferably, the ratio of the crystallization zone is between 25%. Between % and 45%.

By controlling the crystallization ratio of the intrinsic semiconductor 32 to be between 25 and 65% and the grain size to be no more than 30 nm, more energy bands can be introduced in the intrinsic semiconductor 32 to form a multi-gap structure to increase different wavelengths. Light absorption, which increases the photocurrent of the output.

In addition, the microcrystalline germanium structure can be introduced into the N-type semiconductor 33 and the P-type semiconductor 31 at the same time, which not only improves the illumination stability of the solar cell, but also can increase the height, the medium, and the amorphous germanium film 3 of the solar cell of the present invention. In the low energy level, the structure of the multi-energy gap and the multi-energy band is further formed, and the light absorption of different wavelengths can be more effectively increased, and the photocurrent of the output can be improved; preferably, the crystallinity of the N-type semiconductor is Between 50% and 80%, the surface roughness is 2~15nm, and the grain size of the crystalline state is between 10nm and 100nm, and the Si-H bond strength at 2070~2100cm ^-1 is crystallized. Between 45 and 85% of the ratio, the crystallinity of the P-type semiconductor is between 10 and 30%, and the crystal grain size of the crystalline state is between 5 nm and 20 nm, and it is located at 2070 to 2100 cm ^-1 . The Si-H bond strength is between 15 and 35% of the crystallization ratio.

The deposition process pressure is 20mtorr, and the surface roughness and carrier mobility of the amorphous germanium semiconductor film prepared by different deposition power and deposition gas ratio, and the crystallinity of the intrinsic semiconductor are respectively arranged as shown in Table 2 and Table 3. Show.

In the preferred embodiment, the P-type semiconductor 31 and the N-type semiconductor 33 are respectively P-type amorphous germanium and N-type amorphous germanium doped by group III and group V elements, and the intrinsic semiconductor 32 is composed of The base material is composed of a crystalline state of nanocrystalline germanium and an amorphous state of amorphous germanium. The crystallinity of the N-type semiconductor is between 50 and 80%, and the crystallite size of the crystalline state is between 10 nm and ~ 100 nm, and its Si-H bonding strength at 2070-2100 cm ^-1 is between 45 and 85% of the crystallization ratio, and the crystallinity of the P-type semiconductor is between 10 and 30%. The grain size is between 5 nm and 20 nm, and the Si-H bond strength at 2070~2100 cm ^-1 is between 15 and 35% of the crystallization ratio, and the order of energy is about 1.5 to 1.8 eV. The structure of the amorphous germanium film 3 of the P-type semiconductor 31, the intrinsic semiconductor 32, and the N-type intrinsic semiconductor 33 of 1.3 to 1.6 eV and 1.2 to 1.4 eV.

The top electrode 4 is formed on the amorphous germanium film 3, and the transparent conductive film 22 can cooperate with the transparent conductive film 22 to output the electric energy generated by the amorphous germanium film 3. In the preferred embodiment, the top electrode 4 is selected. It is self-aluminum and has a surface roughness of 2 to 15 nm.

The nanocrystalline germanium of the intrinsic semiconductor 32 of the present invention is located in the amorphous germanium, and since the nanocrystalline germanium has better conductivity than the amorphous germanium - the carrier mobility ratio of the nanocrystalline germanium Generally, the amorphous germanium film is one to two orders of magnitude higher, and the dark conductance value is between 10 ^-5 and 10 ^-7 (S.cm ^-1 ), which is 3-4 orders of magnitude higher than the general amorphous germanium. At the same time, the nanocrystalline germanium has better light absorption characteristics and illumination stability than the amorphous germanium, thereby preventing the recombination of electrons and holes in the defect structure of the amorphous germanium, and improving the open circuit of the solar cell. The voltage increases the conversion efficiency of the amorphous germanium solar cell, and also reduces a large number of defects in the amorphous germanium structure and the unbonded anchoring button, which can attenuate the battery efficiency under strong light irradiation, and can improve solar energy. Battery life.

Referring to FIG. 3 and FIG. 4, FIG. 3 shows a Raman spectrum diagram of an intrinsic semiconductor prepared by diluting a ratio R (R=H ₂ /SiH ₄ ) at a hydrogen power density of 0.55 W/cm ² . Figure 4 shows the FT-IR analysis of an intrinsic semiconductor prepared with R = 30, RF power of 1200 W, and a deposition pressure of 30 mtorr.

As can be seen from Fig. 3, the peaks at R = 10, R = 20, and R = 30 are all around 480 cm ^-1 . When R=40, the peak of 510~520 cm ^-1 begins to appear in the figure. Compared with the crystallinity, it can be found that when the hydrogen dilution ratio is gradually increased to R=40, the crystallinity will rise slowly, where R=H ₂ /SiH ₄ .

Referring to FIG. 4, curve 1 in FIG. 4 is an FT-IR spectrum of the intrinsic semiconductor, curves 2 and 3 are crystal regions of the intrinsic semiconductor, and curves 4 and 5 are amorphous regions of the intrinsic semiconductor, and curve 4 is The absorption peak represents the Si-H bond of amorphous yttrium (a-Si:H), and the absorption peak of curve 5 is the methane (SiH ₄ ) of the intrinsic semiconductor during the deposition process because the dissociation is incomplete or in the reaction process. The Si-H bond of the agglomerate (SiH ₃ ) formed in the middle, and the curve 2 with the absorption peak between 2070 and 2100 cm ^-1 represents the denser and less defective microcrystalline germanium and naphthalene in the crystalline region. The Si-H bond of the rice bismuth, the absorption peak of the curve 3 indicates the Si-H bond in which the crystal structure is loose and has many defects, and the Si-H spectrum analysis results of each region show that The Si-H bond of the embodiment between 2070 and 2100 cm ^-1 accounts for about 56%.

In summary, the present invention can not only improve the crystal stability of the solar cell, but also improve the crystal stability of the solar cell by separately or simultaneously controlling the crystallinity of the intrinsic semiconductor, the N-type semiconductor, and the P-type semiconductor. In the high, medium and low energy levels of the amorphous germanium film of the solar cell, a multi-energy gap and multi-energy band structure is further formed, which can more effectively increase the light absorption of different wavelengths, and can improve the output photocurrent. The object of the invention can indeed be achieved.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

2‧‧‧Substrate

21‧‧‧Substrate

22‧‧‧Transparent conductive film

3‧‧‧Amorphous film

31‧‧‧P-type semiconductor

32‧‧‧ Essential Semiconductor

33‧‧‧N type semiconductor

4‧‧‧ top electrode

1 is a schematic view showing a conventional amorphous germanium thin film solar cell structure; FIG. 2 is a schematic view showing a preferred embodiment of the solar cell of the present invention; and FIG. 3 is a Raman spectrogram showing the preferred embodiment of the present invention. The intrinsic semiconductor of the embodiment; and Figure 4 is an FT-IR spectrum showing the absorption peaks of different Si-H bonds of the intrinsic semiconductor of the preferred embodiment of the invention.

2. . . Substrate

twenty one. . . Substrate

twenty two. . . Transparent conductive film

3. . . Amorphous germanium film

31. . . P-type semiconductor

32. . . Essential semiconductor

33. . . N-type semiconductor

4. . . Top electrode

Claims (10)

A solar cell comprising: an electrically conductive substrate having a substrate and a transparent conductive film formed on the surface of the substrate; an amorphous germanium film formed on the substrate and in ohmic contact with the transparent conductive film a P-type semiconductor having an energy level difference, an N-type semiconductor, and an intrinsic semiconductor having an energy level between the energy levels of the P and N-type semiconductors, the intrinsic semiconductor having a crystallization region and a In the amorphous region, the ratio of the crystalline region is 25 to 65% of the intrinsic semiconductor, the grain size is not more than 30 nm, and the Si-H bonding strength at 2070 to 2100 cm ^-1 is 35~ of the crystalline region. 60%, the amorphous germanium film with nanocrystalline crystal can convert light energy into electrical energy by receiving photovoltaic effect when receiving solar energy; and a top electrode formed on the amorphous germanium film, which can interact with the substrate The electric energy generated by the amorphous germanium film is combined to be output to the outside. The solar cell according to claim 1, wherein the ratio of the crystal region is 25 to 45% of the intrinsic semiconductor. The solar cell according to claim 1, wherein the transparent conductive film and the top electrode have a surface roughness of 5 to 25 nm. The solar cell according to claim 1, wherein the crystallinity of the N-type semiconductor is between 50 and 80%, and the crystallite size of the crystallized state is between 10 nm and 100 nm, and the The Si-H bond strength of 2070~2100cm ^-1 is between 45~85% of the crystallization ratio. The solar cell according to claim 1, wherein the P-type semiconductor has a crystallinity of between 10 and 30%, and the crystallite size of the crystal is between 5 nm and 20 nm, and is located at The Si-H bond strength of 2070~2100cm ^-1 is between 15% and 35% of the crystallization ratio. The solar cell according to claim 1, wherein the electrically conductive substrate has a transparent conductive film composed of a metal oxide having a doped carrier. The solar cell according to claim 6, wherein the transparent conductive film has a crystal size of 5 to 15 nm, and the doping carrier has a concentration of between 1 × 10 ¹⁹ and 4 × 10 ²⁰ cm ^-3 . . The solar cell according to claim 7, wherein the transparent conductive film is made of zinc oxide and has a thickness of between 50 and 800 nm, a transmittance of visible light of not less than 85%, and a sheet. The resistance value is between 5 Ω/□ and 15 Ω/□. The solar cell according to claim 6, wherein the doping carrier has a mobility of 5 to 250 cm ² /Vs. The solar cell according to claim 2, wherein the amorphous germanium film has a surface roughness of between 2 and 15 nm.