Effects of a-Si:H layer thicknesses on the performance of a-Si:H∕c-Si heterojunction solar cells

Abstract

We have fabricated hydrogenated amorphous silicon (a-Si:H)∕crystalline silicon (c-Si) heterojunction solar cells with different a-Si:H layer thicknesses, in order to determine effects of a-Si:H layer thicknesses on the performance of a-Si:H∕c-Si solar cells. The thicknesses of a-Si:H p-i layers formed on a n-type c-Si substrate were controlled accurately on the atomic scale by applying real-time spectroscopic ellipsometry during the a-Si:H growth. With increasing a-Si:H p-i layer thicknesses, the open-circuit voltage (Voc) and fill factor increase drastically up to 40Å (i layer) and 30Å (p layer), whereas the short-circuit current density (Jsc) reduces gradually. By using optimum a-Si:H layer thicknesses (i∕p=40∕30Å), we obtained a solar cell efficiency of 16.1% without incorporating surface texture and a back-surface field structure. Quite interestingly, the optimum a-Si:H i-layer thickness (40Å) shows good correlation with a SiH2-rich interface structure formed at the a-Si:H∕c-Si heterointerface, suggesting that the optimum i-layer thickness is governed by the interface properties of the a-Si:H∕c-Si. Quantum efficiency measurements further revealed that the influence of a-Si:H layer thickness on the solar cell is quite different between a-Si:H p and i layers. Based on results obtained from this study, we discuss the roles of a-Si:H p-i layers incorporated in a-Si:H∕c-Si heterojunction solar cells.