Microcrystalline silicon carbide window layers in thin film silicon solar cells

Crystalline silicon carbide alloys have a very high potential to be used as transparent conductive window layers in thin-film solar cells provided they can be prepared in thin-film form and at compatible deposition temperatures. Using Hot-Wire Chemical Vapor Deposition (HWCVD) technique, silicon carbide in microcrystalline form (μc-SiC:H) has been prepared at low substrate temperature. Monomethylsilane and hydrogen are used as the precursor gases. The material is highly conductive, unintentionally n-type in nature, and possess wide optical gap. These properties have been utilized by employing the μc-SiC:H layer as the window layer in n-side illuminated single junction microcrystalline silicon (μc-Si:H) solar cells. Some typical issues related to this device research and development are described here. In particular the nucleation of the intrinsic μc-Si:H absorber layer on the n-type μc-SiC:H layer needs attention. With proper device design high short-circuit current densities of 29.6 mA/cm2 and quantum efficiencies up to 90% are obtained resulting in a maximum conversion efficiency of 9.6% within a 2-μm-thick μc-Si:H solar cell.