AbstractsPhysics

The plasma-enhanced chemical vapour deposition (PECVD) method is widely used compared to other methods to deposit µc-Si:H because of the high potential to prepare high quality material uniformily on a large area substrate at low temperature. This method was used to grow µc-Si:H p- and i-layers. The effect of p– layer deposition parameters on the short– wavelength response of µc-Si:H solar cells is investigated. We also investigated the influence of deposition parameters on the properties of the µc-Si:H absorber layer deposited at the a-Si:H/ µc-Si:H transition. Parameters such as RF power, silane concentration, and deposition pressure were studied. The effect of these parameters on the material properties of intrinsic µc-Si:H layers and the device performance of single junction µc-Si:H solar cells is presented. The results show that p-layer deposited at 300 seconds with 0.2 sccm diborane flow has the optimum value with respect to transparent and conductive nature. It gave a high FF and Voc when applied in a single junction p-i-n type µc-Si:H solar cells with efficiency of 5.4%. Significant gain in quantum efficiency of the solar cell was observed especially in the short-wavelength region. With the optimized p-layer and at 80 W deposition power, the quantum efficiency increased to about 65% at 400 nm when compared to the obtained value of about 35% with the same optimized p-layer deposited at 60 W. The overall results show that the spectral response is highly sensitive to diborane flow at short wavelength. The result of i-layer sensitivity study reveals µc-Si:H i-layer deposited at a low power but higher pressure has high photoresponse. The structural properties of these layers shows defects which may be related to the grain boundries and material contamination due to stress. This was evident as the film oxidizes immediately it is brought out of the deposition system for FTIR analysis, leaving the substrate with little or no films.