Influence of Intrinsic Layer Thickness in the Emitter and BSF of HIT Solar Cells

Abstract

A symmetric structure has been generally used to fabricate heterojunction with intrinsic thin layer (HIT) solar cells, i.e. hydrogenated amorphous silicon (a-Si:H) forms the emitter (i-p stack) and the back surface field (BSF) (i-n stack), and transparent conductive oxide (TCO) covered with metallic electrodes is used on either side. In this contribution, we present the influence of the intrinsic a-Si:H layer thickness in both the emitter and BSF on the passivation and solar-cell performance. Using a thicker intrinsic a-Si:H layer in the emitter results in a longer effective minority carrier lifetime, indicating a better passivation of the a-Si:H/c-Si interface and leading to a higher open-circuit voltage (Voc). In the BSF, thinner or even no intrinsic a-Si:H can be used to increase FF. In both the emitter and BSF, the fill factor (FF) is strongly related to the intrinsic a-Si:H layer thickness. In our investigation, the short circuit current density (Jsc) does not change obviously with the variation of the intrinsic a-Si:H layer thickness. In the case that a full metal contact is used on the BSF side, the solar cell without back TCO shows a better performance. An efficiency of 17.5% is obtained in the flat HIT solar cell without intrinsic a-Si:H passivating layer and TCO on the side of BSF.