Investigation On Crystalline Silicon Surface Passivation By Changing The Deposition Condition Of AlO_x By Atomic Layer Deposition

Solar energy is one of the most valuable clean energy. Solar cell,the most effective way of solar energy application, has been concerned by people from the world. The efficiency of the photovoltaic conversion is a key parameter in the area of solar cell. Now, crystalline silicon(c-Si) solar cells play a very important role in the photovoltaic area due to the high conversion efficiency. In order to reduce the cost of solar cells, the thickness of solar cell is thinner and thinner. Then surface passivation arises at the moment,which can reduce the surface recombination velocity(SRV) of minority carriers, and improve “c and Voc of solar cells, and thus the photoelectric conversion efficiency can be improved as well. Atomic layer deposition(ALD) technique is widely researched duing the uniform AlOx films. But for the surface passivation of c-Si’ which still needs further system research. In this experiment,depositing AlOx thin films on p-type textured c-Si surface by ALD, then the theory of surface passivation and the best deposition conditon by changing the deposition conditions are studied.Specific studies are as follows:1)Using the method of ALD deposited AlOx film on the surface of p-type textured c-Si, by changing the substrate temperature(t),analyzing the passivation mechanism of AlOx thin films to draw the passivation performance of influence of the deposition temperature. In addition, all samples before and after annealing was investigated by Quasi Steady State Photo Conductance(QSSPC). The experiment shows that when t = 250℃,The effective minority carrier lifetime(_eff) of samples reached a maximum value(32.4μs). The Capacitance-Voltage(C-V) was also been investigated. It can be found that there shows a shift of C-V curves in positive direction with the AlOx thin film samples,indicating the existence of negative equivalent oxide charge density(Q_f).2)Various thickness of AlOx thin films were fabricated on the same samples by ALD. and fixed t=250℃,by changing the growth cycle to control the thickness of AlOx film. The thickness of AlOx thin films were altered through changing the deposition cycles. Through adjusting the thickness of AlOx thin films, the optical and electrical properties were significant improved. The reflectance of various thickness of AlOx thin films were decreased from 10.12 % to 0.96 % with the increasing of thickness in a wide spectral range from 350 to 1000 nm,which is demonstrated that the AlOx thin films show an effective antireflection properties. Moreover, the passivation effect of AlOx thin films was identified by using QSSPC. The value of_eff exhibits a significant improved with the variety of film thickness from 9.75 jis to 112.2 |as. The C-V was induced to explain the increasing of Xeff.the high Qf =9.51×10~12 cm~-2 indicates that the AlOx thin films can provide significant field-effect passivation effects through suppressing the surface recombination. While the density of interface traps(Dit =6.08×10~11cm ~-2eV~-1) is not the lowest density value, which means that field-effect passivation effect is more obvious for p type semiconductor.