Back surface field approach: Surface and interface defect states optimization of high efficient Si-ZnO based heterojunction solar cell

Abstract

An Al/n−type a−ZnO/i−ZnO/c−Si(Interface)/p−typec−Si/c−Si(Interface)/c−Si1−xOx:H/Al heterojunction based solar cell is proposed. Silicon based heterojunction solar cells are popular due to the use of transparent zinc oxide as emitter layers, but their efficiency must be increased at low cost. In addition, majority carrier collection at the back surface field reflector-metal contact is low due to high surface defect states. In this work, a reasonable increase in minority carrier lifetime and a decrease in emitter saturation current density, which boost up the efficiency and the fill factor, are simulated by the optimization of interface defect density. The effective modelling of density of states for all device layers resembling practical data is done. The proper optimization of device structures revealed an efficiency of up to 21.23% and a fill factor of 75.71% at with an external series resistance of 2 Ω cm2. A theoretical approach manifesting design criteria for an effective collection of majority carriers is proposed.