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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 1: Focus: Organic Solar Cells Based on Non-fullerene Acceptors: Loss Mechanism and Options for Above 20 % Efficiencies I
CPP 1.2: Talk
Monday, March 27, 2023, 10:00–10:15, GÖR 226
Can Organic Solar Cells Beat the Near-Equilibrium Thermodynamic Limit? — Tanvi Upreti1, •Constantin Tormann2, and Martijn Kemerink1,2 — 1Complex Materials and Devices, Department of Physics, Chemistry and Biology (IFM), Linköping University, Sweden — 2Insitute for Molecular Systems Engineering and Advanced Materials, Heidelberg University, Germany
Switching to non-fullerene acceptors has led to an impressive increase in power conversion efficiencies (PCEs) of organic photovoltaic cells over the past decade. Despite this, the PCE of such devices is still below the near-equilibrium limit of the corresponding material, which is particularly evident from losses in the open-circuit voltage (Voc). A prominent yet incompletely understood loss channel affecting Voc is the thermalization of photogenerated charge carriers in the density of states, which is broadened by energetic disorder. In contrast to symmetric morphologies like classic bulk heterojunctions, morphologies with a gradient in the donor:acceptor ratio can mitigate this loss channel by rectifying the diffusive motion of the thermalizing photogenerated charge carriers. Here, we show by extensive numerical modelling how funnel-shaped donor and acceptor-rich domains in a phase-separated morphology promote directed transport of positive and negative charge carriers towards the anode and cathode, respectively. In such optimized funnel morphologies, this kinetic, nonequilibrium effect even allows one to surpass the near-equilibrium thermodynamic limit for the same active material in the absence of gradients.