The recorded open-circuit voltage and fill factor achievement of a-Si:H p-i-n/HIT-type tandem solar cells by tuning up the crystalline in tunneling recombination junction layer
In this study, a recorded high open-circuit voltage (Voc) of 1.61 V and fill factor (FF) of 76.65% of a-Si:H p-i-n/heterojunction with intrinsic thin layer (HIT)-type multi-junction solar cells were achieved using grain size enlargement within the p-type μc-Si:H layer in a p-type μc-Si:H/n-type a-Si:H tunneling recombination junction (TRJ) layer. The p-type μc-Si:H layer's conductivity increased from 1.74 × 10−4 to 0.1 S cm−1 as the film's crystallinity increased from 41.5% to 67.5%. The a-Si:H p-i-n/HIT-type multi-junction solar cells also benefited from the tuning up crystalline p-type μc-Si:H layer, showing the increase of Voc and FF from 1.5 V and 49.88% to 1.61 V and 76.65%, respectively; while the short-circuit current density (9.38 ± 0.2 mA cm−2) did not change significantly. These are the highest Voc and FF values achieved in a-Si:H p-i-n/HIT-type multi-junction solar cells, recently. From dark current-voltage analysis, it was deduced that the enhanced crystalline films could assist in suppressing carrier interference in the TRJ layer, thus reduces electric field distortion and mitigates recombination in the device. In summary, an enhanced crystalline p-type μc-Si:H layer could be a viable option for ensuring an excellent TRJ layer, thus achieved high efficiency of inorganic/c-Si tandem solar cells. Using optimal condition with crystallinity of 74.1%, the photovoltaic parameters of the device yield Voc, Jsc and FF of 1.51 V, 13.01 mA cm−2 and 71.45%, which in turned giving an efficiency of 14.04% for a-SiGe:H p-i-n/HIT-type tandem solar cell.