Reliable extraction of organic solar cell parameters by combining steady-state and transient techniques

A method to extract reliable material and device parameters of organic solar cells is presented. We employ a comprehensive numerical device model to simulate the solar cell operation in transient and steady-state condition. Parameter extraction with numerical simulation is error-prone because model parameters are often correlated, their unique determination is very difficult and extracted parameters are likely to be inaccurate. We combine the current-voltage characteristics, the photo-CELIV currents (charge extraction with linearly increasing voltage) and the photocurrent response to a light pulse to reduce parameter correlation and increase accuracy and reliability of the extracted parameters. With a correlation matrix analysis it is shown that parameter correlation is significantly reduced when combining several experimental data sets compared with the analysis of current-voltage curves only. We find a set of parameters to reproduce the complete series of measurements with the numerical simulation. The full electrical behavior can be described using a basic drift-diffusion model with constant mobilities and direct photon-to-charge conversion. With this model we extract charge carrier mobilities in the order of 10(-4) cm(2)/V s, a Langevin recombination prefactor of 0.08, charge injection barriers equal at both sides in the range of 0.25 eV and further device parameters for a BHJ cell with PT5DPP as donor and PCBM (C70) as acceptor. The solar cell is simulated with the extracted parameters and internal distribution of electrons, holes and the electric field are visualized. (C) 2012 Elsevier B.V. All rights reserved.