Hot kinetic model as a guide to improve organic photovoltaic materials

Abstract

The modeling of organic solar cells (OSCs) can provide a roadmap for their further improvement. Many OSC models have been proposed in recent years; however, the impact of the key intermediates from photons to electricity-hot charge-transfer (CT) states-on the OSC efficiency is highly ambiguous. In this study, we suggest an analytical kinetic model for OSC that considers a two-step charge generation via hot CT states. This hot kinetic model allowed us to evaluate the impact of different material parameters on the OSC performance: the driving force for charge separation, optical bandgap, charge mobility, geminate recombination rate, thermalization rate, average electron-hole separation distance in the CT state, dielectric permittivity, reorganization energy and charge delocalization. In contrast to a widespread trend of lowering the material bandgap, the model predicts that this approach is only efficient along with improvement of the other material properties. The most promising ways to increase the OSC performance are decreasing the reorganization energy, i.e., an energy change accompanying CT from the donor molecule to the acceptor, increasing the dielectric permittivity and charge delocalization. The model suggests that there are no fundamental limitations that can prevent achieving the OSC efficiency above 20%.

Barrierless Free Charge Generation in the High‐Performance PM6:Y6 Bulk Heterojunction Non‐Fullerene Solar Cell

“…Several studies showed high EQE to be related to a larger driving force . This situation reminds of the “hot” dissociation model, where exciton dissociation creates a more loosely bound electronically/vibronically excited CT state . A popular method to address this issue is to measure the photocurrent response as a function of excitation energy, comprising the spectral range which only excites low lying CT states.…”

Emerging solar cells energy trade-off: Interface engineering materials impact on stability and efficiency progress

“…Low temperature processed PSC grain boundaries, defect related electron diffusion or ion migration limits V oc . Poor interface or aging effect related extraction instability addressed in several recent reports . IEM band edge alignment to the active materials and contact metals work function influence in ESC are reported in numerous studies .…”

“…High EP of PSC material resolves either low exciton binding energy or nonexcitonic carrier separation that enhances V oc by implementing coherent interface layer . Energy conversion route, greater EP ropes to hot CT state for optical gain that ultimately enhances stability and efficiency of PSC and OSC . Advanced IEM band edge, EP, and greater conduction supports to enrich V oc and minimizes instability .…”

“…Energy conversion route, greater EP ropes to hot CT state for optical gain that ultimately enhances stability and efficiency of PSC and OSC . Advanced IEM band edge, EP, and greater conduction supports to enrich V oc and minimizes instability . Hence, OSC and PSC optical to electrical energy transfer track loss is sensibly linked to the active‐interface materials, its architecture and functional properties .…”

“…The optical energy absorption route, thermal energy, and CT state are ensued in OSC. CT state is potentially linked between thermal diffusion and Coulomb's energy . The Coulomb's model inter‐band CS is defined as Coulomb's energy .…”