Energetics and Kinetics Requirements for Organic Solar Cells to 2 Break the 20% Power Conversion Efficiency Barrier

TL;DR

This paper develops an analytical framework to understand how energetics and kinetics of excitons, charge transfer, and charge separated states influence the efficiency of organic solar cells, aiming to surpass 20% power conversion efficiency.

Contribution

It introduces a detailed balance-based analytical model that links energetics and kinetics to photovoltaic performance in organic solar cells, highlighting new design principles.

Findings

Photocurrent generation depends on the interplay of energetics and kinetics.

Optimal equilibrium between species enhances efficiency.

Kinetic rate constants significantly impact photovoltaic parameters.

Abstract

The thermodynamic limit for the efficiency of solar cells is predominantly defined by the energy bandgap of the used semiconductor. In case of organic solar cells both energetics and kinetics of three different species play role: excitons, charge transfer states and charge separated states. In this work, we clarify the effect of the relative energetics and kinetics of these species on the recombination and generation dynamics. Making use of detailed balance, we develop an analytical framework describing how the intricate interplay between the different species influence the photocurrent generation, the recombination, and the open-circuit voltage in organic solar cells. Furthermore, we clarify the essential requirements for equilibrium between excitons, CT states and charge carriers to occur. Finally, we find that the photovoltaic parameters are not only determined by the relative energy level between the different states but also by the kinetic rate constants. These findings provide vital insights into the operation of state-of-art non-fullerene organic solar cells with low offsets.