Reserch Of Silicon Thin Film Tandem Solar Cells Based On Microcrystalline Silicon Solar Cells Deposited In A Single Chamber

For silicon thin film solar cells, high photoelectric conversion efficiency of the solar cell and low cost are two key issues. Tandem solar cells based on microcrystalline silicon solar cells deposited in a single chamber can make much more use of solar spectrum and then has a great potential to increase the conversion efficiency. Plasma deposition of thin film silicon based solar cells in a single-chamber reactor leads to considerable simplifications and reduced costs as compared to multi-chamber processes. So, Tandem solar cells deposited in a single chamber system become a hot research topic of photovoltaic technology. In this thesis, based on the a-Si:H solar cells made by our laboratory or the a-Si:H/a-Si:H tandem solar cells realized in industry using completely single chamber deposition technique, Tandem solar cells based on microcrystalline silicon solar cells deposited in a single chamber were studied. The main research topics and results are described as follows.First of all, Combining Raman and AFM analyses, effect of pre-hydrogen glow discharge on initial growth of intrinsic microcrystalline silicon thin film were systematically investigated. The short circuit current density (Jsc) and open circuit voltage (Voc) were controlled though adjusting silicon concentration and deposition power.1. Considering the importance of initial growth of intrinsic microcrystalline silicon thin film for the subsequent bulk growth and p/i interface in p-i-n solar cells, in this thesis, pre-hydrogen glow method was used to improve nuclei density and reduce the thickness of amorphous incubation layer. The nuclei density obviously affects the subsequent bulk growth and also made the film more compact.2. Considering the significant relationship between the performance ofμc-Si:H solar cells andμc-Si:H thin film structure evolution along the growth direction, in this thesis, silicon concentration and deposition power were adjusted to controlμc-Si:H structure evolution along the growth direction. The result indicates that the performance ofμc-Si:H solar cells mainly depends on the well controlledμc-Si:H structure evolution along the growth direction, but the Jsc and Voc related with p/i interface and initial growth of intrinsic microcrystalline silicon thin film. The above result is very beneficial for modifying tandem solar cells based on microcrystalline silicon solar cells.3. Through the optimization of i layer and p/i interface inμc-Si:H solar cells and incorporation of light trapping,μc-Si:H solar cell with 7.47%(Area=1cm2) initial conversion efficiency was fabricated on a ZnO substrate with certain texture.Secondly, the performance of the micromorph tandem cells were improved by varyingμc-Si:H i-layer thinckness, silane concentration, and pre-hydrogen plasma time.1. Current matching of component cells is very important for tandem cells. In this thesis, fixed the thinckness of top cells at 250nm, current can be matched by adjusting the thinckness of bottom cell i-layer.2. Based on current matching of component cells, silane concentration for the i-layer of bottom cells was optimized for enhancing the performance of a-Si:H/μc-Si:H tandem solar cells.3. Pre-hydrogen plasma had an impact on the performance of p/i interface. Through optimizing pre-hydrogen plasma time, open circuit voltage and conversion efficiency of solar cells were improved.4. An initial conversion efficiency of 11.04% was achieved for micromorph tandem solar cell using ZnO/Al back reflector. Furthermore,100cm2 micromorph tandem module with 9.53% initial conversion efficiency was also obtained.Thirdly, a-Si:H/a-Si:H/μc-Si:H triple junction solar cell were fabricated in a single chamber system.1. Based on the a-Si:H/a-Si:H tandem solar cells realized in industry using single chamber deposition technique, H plasma glow was introduced to etch oxide on the surface, then aμc-Si:H n layer was deposited to obtain good n/p junction.2. a-Si:H/a-Si:H/μc-Si:H triple junction solar cells with 9.52% conversion efficiency have been successfully fabricated by changing deposition conditions for n/p tunnel junction andμc-Si:H bottom solar cells in a single chamber developed by our own. The photoelectric conversion efficiency of a-Si:H/a-Si:H tandem solar cells a-Si:H/a-Si:H/μc-Si:H triple junction solar cells show a increase of more then two percent improved efficiencies compared to a-Si:H/a-Si:H tandem solar cells realized in industry.