Extracting Microscopic Device Parameters from Transient Photocurrent Measurements of P3HT:PCBM Solar Cells

Abstract

AbstractBy including trap‐limited recombination in a time‐domain drift‐diffusion model of a P3HT:PCBM solar cell, experimental transient photocurrent (TPC) measurements across the current–voltage (J–V) curve in both the light and the dark can be reproduced. Using the same set of model parameters, the steady‐state current–voltage curves and charge‐extraction data are also reproduced. The model is validated by predicting the recombination rate at open circuit and comparing results with the rate as measured by the transient photovoltage (TPV) measurement technique. It is demonstrated that the model, which incorporates transport, carrier trapping, carrier de‐trapping, and recombination, is able to reproduce device dynamics correctly. The fit of the model to the experimental results is improved by varying the shape of the electron and hole density of state (DoS) functions. By discretizing the DoS in energy space and allowing its shape to vary, the TPC transients can be closely fitted and the form of the tails of the electron and hole DoS extracted. It is found that the DoS of trapped carriers can be represented by a series of Gaussians offset in energy. This is tentatively attributed to electronic disorder introduced by molecular packing of the molecules.