N-type hydrogenated microcrystalline silicon/indium tin oxide back-reflector interfacial characterization for micromorph tandem solar cell applications

Abstract

Back-reflectors (BRs) in hydrogenated amorphous Si (a-Si:H)/hydrogenated micro-crystalline Si (μc-Si:H) solar cells must not only have sufficient properties to efficiently retrieve the unabsorbed light to where it can be used but must also have lesser back-interfacial states, which are needed for efficient carrier collection. In this study, in order to study the effects of μc-Si:H(n)/transparent conductive oxide-BRs interfacial properties on the performance of a-Si:H/μc-Si:H tandem solar cells, indium tin oxide (ITO)-BRs films are deposited using different reactive gases (argon (Ar), Ar-hydrogen (H2), and Ar-helium (He)). A higher recombination of μc-Si:H(n)/ITO-BRs interfaces causes lower open-circuit voltage (Voc) and fill factor (FF). For ITO deposited in Ar-He reactive gas, the higher recombination at the interface of μc-Si:H(n)/ITO-BRs may be attributed to the high energetic He ion bombardment; whereas, with the use of Ar-H2 reactive gas, the higher recombination may be attributed to the blocking carrier collection caused by the higher Schottky barrier height. The highest efficiency of 12.04% (Voc: 1422 mV, short-circuit current density: 11.06 mA/cm2, FF: 76.56%) is obtained for ITO-BRs using pure Ar gas. It is worth noting that both the interface damage and the Schottky barrier can impact device performances.