Beyond 25% efficient crystalline silicon heterojunction solar cells with hydrogenated amorphous silicon oxide stacked passivation layers for rear emitter

Abstract

Hydrogenated amorphous silicon oxide (a-SiOx:H) alloy is considered as a promising alternative to hydrogenated amorphous silicon (a-Si:H) in crystalline silicon heterojunction (SHJ) solar cells due to its reduced parasitic absorption induced by the incorporation of oxygen. However, the large valence band offset (ΔEV) between a-SiOx:H and crystalline silicon (c-Si) usually leads to low fill factor (FF) for the solar cells. Here, we designed a trilyer a-SiOx:H(i) stacked passivation scheme underneath the rear emitter (p) for the SHJ solar cell on n-type c-Si wafer via depositing the a-SiOx:H(i) layers with different oxygen contents by plasma-enhanced chemical vapor deposition (PECVD). Highly efficient SHJ solar cells with the average efficiency of 25.37% were obtained by optimizing the trilayer a-SiOx:H(i) passivation structure with an oxygen-rich layer inserted between two oxygen-less layers. Comparing to the solar cells with complete a-Si:H passivation layers, higher short-circuit current density (JSC) and open-circuit voltage (VOC) of the solar cells were achieved, which indicated excellent passivation and low parasitic absorption contributed from the a-SiOx:H(i) stacked layers. At the same time, FF of the solar cells was also increased slightly. The corresponding improvement mechanisms were analyzed carefully. As a demonstration, the highest efficiency of the SHJ solar cells passivated by the trilayer a-SiOx:H(i) scheme for rear emitter was up to 25.44%.