Organic photovoltaics (OPVs) represent one of the most promising emerging photovoltaic technologies recently showing a rapid push in power conversion efficiency (PCE). However, this improvement is rather explained by a larger explored phase space of available materials than by a detailed understanding of the fundamental properties limiting the efficiency. Existing studies of efficiency limits in OPVs rely on ensemble descriptions of the light conversion into electrical energy [1]. Entropy appears to play an important role in one of the fundamental physical processes, the separation of strongly bound electron-hole pairs (CT state) into free charge carriers [2]. However, a microscopic theory capturing its non-equilibrium nature is of need, as the separation of the CT state strongly varies due to the amorphous character of OPVs andelectrostatic interactions with the environment. Stochastic thermodynamics [3,4] allows measuring quantities which vary from one experiment to another. It describes stochastic properties of small scale physical systems and allows to analyze nonequilibrium properties. Using the second law of thermodynamics in its stochastic description [3], one can compute the entropy production based on the trajectory of the system state , which is described in a stochastic manner by system transition rates . In this work, we extend our previously developed kinetic Monte Carlo model for OPVs [5]to compute non-equilibrium thermodynamic properties such as energy dissipation and entropy production using trajectory thermodynamics. We study the role of the non-equilibrium nature of the CT state separation and break down the energy losses into the microscopic physical processes considering charge transport, radiative and non-radiative recombination, photon absorption, and CT state separation. In addition, we derive efficiency limits from ensemble averages and compare them with existing limits derived from ensemble thermodynamics [1] [1] N.C. Giebink, et al. Phys. Rev. B 83.19 (2011): 195326. [2] S.N. Hood, and I. Kassal.J. Phys. Chem. Lett. 7.22 (2016): 4495-4500. [3] C. van den Broeck, and M. Esposito. Phys. A 418 (2015): 6-16. [4] U. Seifert. Rep. Prog. Phys. 75.12 (2012): 126001. [5] J. Popp, W. Kaiser, and A. Gagliardi. Adv. Theory Sim. (2019): 1800114.     «

Organic photovoltaics (OPVs) represent one of the most promising emerging photovoltaic technologies recently showing a rapid push in power conversion efficiency (PCE). However, this improvement is rather explained by a larger explored phase space of available materials than by a detailed understanding of the fundamental properties limiting the efficiency. Existing studies of efficiency limits in OPVs rely on ensemble descriptions of the light conversion into electrical energy [1]. Entropy appear...     »