Understanding Carrier Lifetime in Inverted Polymer Solar Cells with a Thick Electron Selective Layer

Charge carrier life-time in an inverted solar cell is studied as a function of differing thickness of biopolymer-based electron selective layer (ESL) using transient photovoltage (TPV) spectroscopy. Longer carrier lifetimes were obtained for devices with a thicker ESL layer, indicating better device performance. However, thick ESL devices showed lower charge mobility and poorer solar cell performance from double injection current (DI) spectroscopy and current density-voltage (J-V) measurements respectively as compared to thin ESL devices. The origin of this discrepancy is found to be due to enhanced charge carrier trapping in the thick ESL layer as supported by capacitance-voltage (C-V) measurements. (C) 2014 The Electrochemical Society. All rights reserved.