Predicting the Maximum Open Circuit Voltage of Perovskite Solar Cells from Time-Resolved Measurements
Dengyang Guo a, Valentina Caselli a, Eline Hutter a, Tom Savenije a
a Department of Chemical Engineering, Delft University of Technology, 2629 HZ Delft, The Netherlands.
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Dengyang Guo, 018
Publication date: 11th February 2019

While the power conversion efficiency of perovskite solar cells has increased enormously in the past decade, the open circuit voltage, Voc, is still below the conceivable limit. Hence, understanding the factors governing and the improvement of the Vocis essential to exploit the full potential of metal halide perovskites (MHPs). Recently, different academic groups reported that the Voc of perovskite solar cells is not determined by the Fermi levels of the transport materials but more related to the Quasi-Fermi level splitting, μF, of the perovskite layers under illumination. Here, we show a generic method to derive the steady-state Quasi-Femi level splitting from basically any pulsed excitation experiment such as TRMC, THz or TA on bare, non-contacted perovskite films. We first present a kinetic model, which is able to fit time-resolved photoconductance traces recorded over almost four orders of magnitude with one set of rate constants and parameters. Next, using these fitting results we calculate the concentrations of excess electrons and holes under continuous AM1.5 excitation. Finally, μis calculated from the steady-state excess charge carrier concentrations. This new method is applied to previously reported MHP cells and shows that the Voc can approach μF/e closely. We then analyze the kinetic parameters which provide hints to further improve μF/e and hence the Voc. The present method could help to evaluate new perovskite materials, structures or post treatments in an early stage, avoiding the labour-intensive effort to make fully optimized devices.

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