Effect of H treatment on performance of HIT solar cells

Hydrogen is a ubiquitous element in semiconductor processing and particularly in amorphous and microcrystalline silicon where it plays a crucial role in the growth processes as well as in the material properties. Because of its low mass it can easily diffuse through the silicon network and leads to the passivation of dangling bonds but it may also play a role in the stabilization of metastable defects. Thus a lot of work has been devoted to the study of hydrogen diffusion, bonding and structure in disordered semiconductors. The sequence, deposition-exposure to H plasma-deposition was used to fabricate the microcrystalline emitter. A proper atomic H pretreatment of c-Si surface before depositions i layer was expected to clean the surface and passivatates the surface states, as a result improing the device parameters. In this study, H2 pretreatment of c-si surface was used at different time, power and temperature. It is found that a proper H pretreatment improves passivation of c-si surface and improves the device parameters by AFM and testing I-V.

Emitter layer optimization in heterojunction bifacial silicon solar cells

Silicon solar cells continue to dominate the market,due to the abundance of silicon and their acceptable efficiency.The heterojunction with intrinsic thin layer(HIT)structure is now the dominant technology.Increasing the efficiency of these cells could expand the development choices for HIT solar cells.We presented a detailed investigation of the emitter a-Si:H(n)lay-er of a p-type bifacial HIT solar cell in terms of characteristic parameters which include layer doping concentration,thickness,band gap width,electron affinity,hole mobility,and so on.Solar cell composition:(ZnO/nc-Si:H(n)/a-Si:H(i)/c-Si(p)/a-Si:H(i)/nc-Si:H(p)/ZnO).The results reveal optimal values for the investigated parameters,for which the highest computed efficiency is 26.45%when lighted from the top only and 21.21%when illuminated from the back only.

Influence of absorber doping in a-SiC:H/a-Si:H/a-SiGe:H solar cells

This work deals with the design evaluation and influence of absorber doping for aSi：H/aSiC：H/a SiGe：H based thinfilm solar cells using a twodimensional computer aided design （TCAD） tool. Various physical parameters of the layered structure, such as doping and thickness of the absorber layer, have been studied. For reliable device simulation with realistic predictability, the device performance is evaluated by implementing nec essary models （e.g., surface recombinations, thermionic field emission tunneling model for carrier transport at the heterojunction, SchokleyRead Hall recombination model, Auger recombination model, bandgap narrowing ef fects, doping and temperature dependent mobility model and using FermiDirac statistics）. A single absorber with a graded design gives an efficiency of 10.1% for 800 nm thick multiband absorption. Similarly, a tandem design shows an efficiency of 10.4% with a total absorber of thickness of 800 nm at a bandgap of 1.75 eV and 1.0 eV for the top aSi and bottom aSiGe component cells. A moderate ndoping in the absorber helps to improve the efficiency while p doping in the absorber degrades efficiency due to a decrease in the Voc （and fill factor） of the device.

Texturization and rounded process of silicon wafers for heterojunction with intrinsic thin-layer solar cells

Heterojunction with intrinsic thin-layer （HIT） solar cells are sensitive to interface state density. Tradi- tional texture process for silicon solar cells is not suitable for HIT one. Thus, sodium hydroxide （NaOH）, isopropanol （IPA） and mixed additive were tentatively introduced for the texturization of HIT solar cells in this study. Then, a mixture including nitric acid （HNO3）, hydrofluoric acid （HF） and glacial acetic acid （CH3COOH） was employed to round pyramid structure. The morphology of textured surface and the influence of etching time on surface reflectance were studied, and the relationship between etching time and surface reflectance, vertex angle of pyramid structure was analyzed. It was found that the mixture consisting of 1.1 wt% NaOH, 3 vol% IPA and 0.3 vol% additives with etching time of 22.5 min is the best for H1T solar cells under the condition of 80℃. Uniform pyramid structure was observed and the base width of pyramid was about 2-4 μm. The average surface reflec- tance was 11.68%. Finally the effect of different processes on the performance of HIT solar cells was investigated. It was shown that these texturization and rounding techni- ques used in this study can increase short circuit current （Jsc）, but they have little influence on fill factor （FF） and open circuit voltage （Voo） of HIT solar cells.

Effect of chemical polish etching and post annealing on the performance of silicon heterojunction solar cells

Amorphous/crystalline silicon heterostructure solar cells have been fabricated by hot wire chemical vapor deposition （HWCVD） on textured p-type substrates. The influence of chemical polish （CP） etching and the post annealing process on the solar cell performance have been studied. The CP treatment leads to a reduction of stress in the i-layer by the slight rounding of the pyramid peaks, therefore improving the deposition coverage and the contact by each layer, which is beneficial for the performance of the solar cells. An optimized etching time of 10-15 s has been obtained. A post annealing process leads to a considerably improved open voltage （Voc）, filled factor （FF）, and conversion efficiency （η） by restructuring the deposited film and reducing the series resistance. An efficiency of 15.14% is achieved that represents the highest result reported in China for an amorphous/crystalline heterostructure solar cells based on the textured p-type substrates.