Research On Periodic Electrode For Silicon Based Thin Film Solar Cells

In both PIN-type and NIP-type thin film silicon solar cells, textured light trapping substrates are important and used to enhance light absorption and improve energy conversion efficiencies. Trapping substrates not only can improve the scattering of the incoming light and optical path to enhance the conversion efficiencies, but also can reduce the interference phenomenon of the incident light to enhance the response of the solar cell. Periodic light trapping structure is good at excellent repeatability, easy to simulate and change the structure, etc. In order to research the excellent periodically transparent conductive front electrode for PIN thin film solar cells and excellent periodically back reflector for NIP thin film solar cells. In this paper, we have taken a detailed study at the preparation method and the factors affecting photoelectric properties of periodically transparent conductive front electrode and periodically back reflector, the main research contents and results are given as follows.(1) We proposed a new sauna-like method for producing hexagonal monolayer and closely arranged polystyrene (PS) microspheres. Steam was applied to cause the PS microspheres to shrink and self-assemble.(2) We proposed a new method for producing periodically transparent conductive front electrode that is PS microspheres as the mask. Reactive ion etching (RIE) with O2 gas was used to first shrink the PS microspheres. An initial ZnO film was then deposited by magnetron sputtering, after which the PS microspheres were removed ultrasonically to leave a substrate with a periodic structure. Finally, a second layer of the ZnO film was deposited on the substrate to ensure excellent electrical properties. We researched the effecting reason such as the material of ZnO, the diameter of the PS microspheres, the etching times of the PS microspheres and the nominal thickness of the ZnO film to the periodically transparent conductive front electrode.To illustrate the effect of the improvement in the optical properties of the periodically transparent conductive front electrode on the solar cell performance, PIN-type μc-Si:H solar cells were fabricated using the proposed periodically transparent conductive front electrode. A high efficiency of 8.33%, a Jsc of 25.9 mA/cm2, all indicated that periodically transparent conductive front electrodes offer many advantages for using in μc-Si:H cells(3) The method of PS microspheres as the mask was also fit for periodically back reflector. Reactive ion etching (RIE) with O2 gas was used to first shrink the PS microspheres. An initial Ag film was then deposited by magnetron sputtering, after which the PS microspheres were removed ultrasonically to leave a substrate with a periodic structure. Finally, a second layer of the Ag film was deposited on the substrate to ensure high reflection. We researched the effecting reason such as the diameter of the PS microspheres, the etching times of the PS microspheres and the nominal thickness of the Ag film to the periodically back reflector.To illustrate the effect of the improvement in the optical properties of the periodically back reflector on the solar cell performance, NIP-type μc-Si:H solar cells were fabricated using the proposed periodically back reflector. A high efficiency of 8.56%, a Jsc of 24.05 mA/cm2, FF of 70.57%, all indicated that periodically back reflector offer many advantages for use in μc-Si:H cells.