Electron-Hole Separation Dynamics and Optoelectronic Properties of a PCE10:FOIC Blend

Abstract: Understanding charge separation dynamics in organic semiconductor blends is crucial for optimizing the performance of organic photovoltaic solar cells. In this study, we explored the optoelectronic properties and charge separation dynamics of a PCE10:FOIC blend, by combining steady-state and time-resolved spectroscopies with high-level DFT calculations. Femtosecond transient absorption spectroscopy revealed a significant reduction of the exciton-exciton annihilation recombination rate in the acceptor when incorporated into the blend, compared to its pristine form. This reduction was attributed to a decrease in exciton density within the acceptor, driven by an efficient hole-separation process that was characterized by following the temporal evolution of the transient signals associated with the excited states of the donor when the acceptor was selectively excited within the blend. The analysis of these dynamics enabled the estimation of the hole separation time constant from the acceptor to the donor, yielding a time constant of (1.3 +- 0.3) ps. Additionally, this study allowed the quantification of exciton diffusion and revealed a charge separation efficiency of approximately 60%, providing valuable insights for the design of next-generation organic photovoltaic materials with enhanced charge separation and improved device efficiency.