18.4%-efficient heterojunction Si solar cells using optimized ITO/top electrode

Abstract

We optimized the thickness of a transparent conductive oxide (TCO) layer, and applied a micro-scale, mesh-pattern metal electrode to prevent efficiency degradation due to current loss caused by the TCO layer and top electrode of an a-Si/c-Si heterojunction solar cell. A solar cell equipped with a micro-grid metal electrode demonstrated a high short-circuit current density (JSC) of 40.1 mA/cm2, and achieved high efficiency of 18.4% with an open-circuit voltage (VOC) of 618 mV and a fill factor (FF) of 74.1%. When compared with conventional bus/finger bar electrodes, the micro-gird metal electrode improved JSC by more than 10% via a shortened carrier path length and a decreased electrode area (more than 50%). Furthermore, by optimizing the process sequence for electrode formation, we could effectively restore the reduction in VOC that occurs during the micro-grid metal electrode formation process. This work is expected to become a fundamental study that can effectively improve current loss in a-Si/c-Si heterojunction solar cells through the optimization of transparent and metal electrodes.