The Critical Role of Temperature-dependent Mobilities in Determining the Open-Circuit Voltage of Bulk-heterojunction Organic Solar Cells
Yahui Tang a b
a Department of Materials Science and Engineering, Monash University, Clayton, Victoria, 3800 Australia, Wellington Rd, Clayton, Australia
b School of Chemistry, The University of Sydney, NSW 2006, Astralia
Proceedings of Device Physics Characterization and Interpretation in Perovskite and Organic Materials (DEPERO)
VALÈNCIA, Spain, 2023 October 3rd - 5th
Organizers: Sandheep Ravishankar, Juan Bisquert and Evelyne Knapp
Oral, Yahui Tang, presentation 018
Publication date: 14th September 2023

The efficiency of solution-processed bulk-heterojunction organic solar cells has continued to increase in recent years and is now approaching 20%. This continued improvement in cell efficiency is maintaining substantial academic as well as commercial interest in this technology. Compared to their inorganic counterparts, the non-radiative energy loss is higher in organic solar cells which limits their open-circuit voltage (VOC) and thus the power conversion efficiency. Therefore, understanding the physical nature of non-radiative energy loss and VOC of organic solar cells is of substantial interest to the community. Studying the temperature dependence of VOC can provide unique insights into the physical origin of non-radiative loss because non-radiative recombination is temperature dependent. In addition, understanding the temperature dependence of VOC is of practical interest because the extrapolation of the VOC vs. temperature curve to 0 K may provide an estimate of the maximum achievable VOC for organic solar cells. In this study, the authors provide a coherent description of the temperature dependence of open-circuit voltage of organic solar cells, combining experimental measurements and numerical simulations. Specifically, the authors have experimentally measured the temperature dependence of charge carrier mobilities which have then been used to simulate the temperature-dependent VOC of organic solar cells. Significantly, it is found that the experimentally measured temperature dependence of open-circuit voltage can be correctly reproduced only if the temperature-dependent mobilities are included. Other factors that can complicate the analysis of the temperature-dependent VOC  will also be covered in the talk including the leakage current,[1] and the different energetic levels at the donor:acceptor interfaces of bulk-heterojunction and bilayer organic solar cells.[2]

This work is supported by the Australian Research Council Centre of Excellence in Exciton Science (funding Grant No. CE170100026).

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