Fabrication of Solar Cells Having SiH2Cl2 Based I-Layer Materials

Abstract

Intrinsic amorphous silicon films were fabricated using electron cyclotron resonance (ECR) assisted chemical vapor deposition and SiH2Cl2 source gas. Intrinsic layers were used for material characterization and also for the absorber layer of solar cells. The highly reducing atmosphere produced by the high energy ECR hydrogen plasma used to deposit these intrinsic films caused some degradation and/or etching of the previously deposited solar cell doped layers as well as the SnO2-coated glass substrates. The p-layer etching rates were greater than those of the n-layer when these layers were exposed to ECR hydrogen plasma. Optimum photovoltaic performance was achieved when an optimized n/i interfacial buffer layer was used for a solar cell deposited in the n-i-p sequence. Better solar cell performances were obtained when the solar cells were measured under n-side illumination. In part, the buffer layer optimization involved careful consideration of band gap matching to the relatively wide band gap (1.85 eV) intrinsic layers prepared from SiH2Cl2. Further performance gains were possible through transparent conductive oxide/substrate optimization. For example, the open circuit voltage (Voc) increased to ∼0.89 V when gallium-doped zinc oxide/glass substrates were used compared to ∼0.63 V when tin oxide/glass substrates were used. Interface recombination and minority carrier diffusion lengths were probed by n- and p-side illuminated quantum efficiency measurement and analysis. The electron and hole µτ products were estimated to be 4.4×10-8 cm2/V and 3.5×10-8 cm2/V, respectively. The stability of the solar cells was also examined.