Research On Phosphorous/Aluminum Gettering And Heterojunction Solar Cells

The wide use of solar cells will be a feasible way to solve the energy and environmental protection problems. The development of solar cells shows a tendency to improve efficiency and reduce cost. Amorphous silicon /crystalline silicon heterojunction solar cells and crystal silicon solar cells are considered as the most promising cells in the future for their advantages, such as high efficiency, great stability, simple processing, and none-pollution.This work is to achieve the high efficient heteroj unction solar cells and improve the efficiency and reduce the cost of crystal silicon solar cells. The contents of this thesis are as follows:Firstly, intrinsic and n-type amorphous silicon films are deposited on the p-type monocrystal silicon by Plasma Enhanced Chemical Vapour Deposition (PECVD), and indium tin oxide film is deposited on n-type amorphous silicon by RF magnetron sputtering to realize the a-Si/c-Si heterojunction solar cells. I-V test and spectral response measurement are used to analyze the characterization of solar cells. The characterization of ITO thin films is studied by XRD, transmittance spectrum, four-point probe and reflection spectrum. It has been found that the different transparent conductive oxide films (ITO and ZnO:Al) can influence the properties of heterojunction solar cell apparently. The vacuum annealing can greatly improve the electrical and optical properties of ITO thin films. After annealing, the 2.18 X 10"4 Q cm resistivity and 90% transmittance are obtained and the efficiency of a-Si/c-Si heterojuntion solar cells is improved greatly.Secondly, the effect of P/AL gettering on crystalline silicon is researched, and applied on the poly-crystalline solar cells. It is described that a series research of heavy phosphorous diffusion gettering, aluminum and combination of aluminum and phosphorous gettering (evaporation of aluminum on the front and back of the wafers) are applied to crystalline silicon. The changes of minority carrier lifetime and concentration of interstitial oxygen are tested after gettering. It is found that the minority carrier lifetime of the poly-crystalline silicon wafers is improved greatly after getterring. The electric performances of 1 x 1 cm2 poly-crystalline silicon solar cell are tested and the electric properties of these cells are contrasted after getterring. The phosphorous aluminum co-gettering is found to be the most effective way in improving the minority carrier lifetime of the poly-crystalline silicon wafers.