Enhanced carrier management and photogenerated charge dynamics for selenium (Se) film photovoltaics

Abstract

Although power conversion efficiency (PCE) of selenium (Se) solar cells has been improved, the device performance is capped by unexpected open-circuit voltage(VOC), short-circuit current (JSC), and fill factor (FF). The Se solar cells with tin oxide (SnO2) as the n-type buffer layer (NBL) have been reported. Here, the polyacrylic acid with carboxylic functional groups was added into the Alfa-SnO2 colloid to impede SnO2 aggregation during spin-coating. The superior Alfa-SnO2 film compactness with improved film coverage can enhance carrier management. The decreased conduction band offset at NBL/Se can promote rapid carrier injection from Se to Alfa-SnO2. Furthermore, the electrostatic attraction between carboxylic groups and Se atoms will passivate interface defects and promote charge extraction. The increased external quantum efficiency with high photovoltaic parameters (VOC, JSC, and FF) will evidently improve the device performance. Ultimately, a high PCE of 5.82% (a VOC of 0.870 V, a JSC of 10.77 mA cm−2, and a FF of 0.621) for the best-performing Se solar cells is achieved. Also, the photogenerated carrier separation, transport, and extraction processes have also been measured to determine the charge dynamics. The conformal P-Alfa-SnO2 films can largely enhance the light-harvesting performance, and the colloidal Alfa-SnO2 will open up a simple and effective way for improving device performance of Se solar cells.