Performance improvement of pin-type amorphous silicon solar cells with wide bandgap materials

Abstract

The purpose of this study is to enhance the conversion efficiency η of pin-type amorphous silicon (a-Si) solar cells with wide bandgap materials. Since the historical demonstration of the gas phase doping of a-Si thin films it has been commonly accepted that the pin configuration is the optimal implementation of a-Si solar cells. At the same time, the pin configuration makes p, n layer as ‘dead’ layer, photo-generated carrier within the p-a-SiC can not be collected due to accumulation state, and light absorption of n-layer reduces Jsc further. Therefore, the η has reached up limit based on the traditional pin configuration. New materials and configuration are needed to enhance the η further. The light absorption within widow layer can be reduced by adapting wide bandgap materials as p layer/or inserting larger work func??tion material between TCO and p layer to change band bending of p-a-SiC into depleted state. The power loss from the absorption at the n-type layer could be minimized by employing wide band gap materials such as silicon oxides. In organic electronics society, transition metal oxide such as tungsten oxide ($WO_3$) and molybdenum oxide ($MoO_3$) have been extensively studied as a buffer layer between the front ITO anode and active layer, and lithium fluoride (LiF) has been successfully used as interlayer between the carrier transport layer and back electrode. The devices performance have enhanced significantly. In this study we will study the possibility to apply these wide bandgap materials in pin-type a-Si solar cells. Firstly, a thermally evaporated $WO_3$ film is introduced as a buffer layer between $SnO_2$ and p-type amorphous silicon carbide (p-a-SiC) of pin-type a-Si solar cells. Using the band diagram it is shown that the $WO_3$ layer lowered the barrier height between the $SnO_2$ and p-a-SiC, which enhances the open circuit voltage and the blue response compared to a bufferless cell. By inserting a 2-nm-thick $WO_3$ layer between $SnO_...