Heterojunction emitter for crystalline silicon thin-film cells

Crystalline silicon thin-film solar cells on a foreign substrate were fabricated using an i-a-Si/n-a-Si heterojunction instead of a diffused phosphorus emitter. The heterojunction was adopted to the rough 10 μm-thin absorber layer with different grain sizes and grain heights. The fabrication of the thin heterojunction structures reduces the thermal budget (max. temperature ≪ 300°C) of the fabrication process and has positive effects on the impurity diffusion from the substrate. We measured the electrical and optical characteristics (current-voltage curve, EQE) of the heterojunction cells and compared them with cells using a diffused phosphorus emitter by rapid thermal diffusion (RTP). The structures with heterojunction resulted in first solar cells with 6.2% efficiency and an increased open circuit voltage (+14 mV) compared to the reference cells.