Slow Relaxation of Photogenerated Charge Carriers Boosts Open-Circuit Voltage of Organic Solar Cells

Abstract

Among the parameters determining the efficiency of an organic solar cell, the open-circuit voltage ($V_{\text{OC}}$) is the one with most room for improvement. Existing models for the description of $V_{\text{OC}}$ assume that photogenerated charge carriers are thermalized. Here, we demonstrate that quasi-equilibrium concepts cannot fully describe $V_{\text{OC}}$ of disordered organic devices. For two representative donor:acceptor blends it is shown that $V_{\text{OC}}$ is actually 0.1-0.2 V higher than it would be if the system was in thermodynamic equilibrium. Extensive numerical modeling reveals that the excess energy is mainly due to incomplete relaxation in the disorder-broadened density of states. These findings indicate that organic solar cells work as nonequilibrium devices, in which part of the photon excess energy is harvested in the form of an enhanced $V_{\text{OC}}$.

arXiv commentFinal version; title changed; journal reference added

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Cited by in corpus (3)

• Jumping kinetic Monte Carlo: Fast and accurate simulations of partially delocalised charge transport in organic semiconductors
• Hot Carrier Organic Solar Cells
• Triplet Excitons Reconcile Charge Generation and Recombination in Low-Offset Organic Solar Cells: Efficiency Limits from a 5-State Model