Insight into light- and static-electric-field-induced polarization on polaron-pair dynamics in neat P3HT device: A transient-absorption-spectroscopy-based study

We have investigated the polaron-pair dynamics following the excitation of vibrationally hot exciton states in organic semiconductor-based optoelectronic devices to better understand the photophysical properties, which can help to improve the device performance. In our earlier work, published at 'Phys. Chem. Chem. Phys., 2019,21, 21236-21248', we have investigated the role of the static electric internal and external fields on the polaron-pair dynamics in a neat poly(3-hexylthiophene-2,5-diyl) based device. From this, we have concluded that the polaron-pair dissociates into charge carriers due to the internal field present inside the device and the dissociation process accelerates when an external electric field is also applied in reverse bias. Apart from the electric-field-induced dissociation process, we now have also been interested in the light- and electric-field-induced polarization effect on the polaron-pair dynamics. For this, in the present study, we have used femtosecond transient absorption spectroscopy to investigate the polaron-pair dynamics in a neat P3HT-based device for different angles of incidence of the light with an additional variation of the static electric field. It is well-known that thin-film photovoltaics can be designed for improved angle-dependent responsivity at specific angles and the photon harvesting efficiency depends on the incident angle of light. Internal electric fields together with the electric field of the incident light both influence the charge generation efficiency of the device, which is determined by the photophysical processes happening between electronic excitation and the formation of charge. The change of reflectivity due to the variation of incident angle and the effect of the electric-field induced polarization make an overall impact on the polaron-pair dynamics as demonstrated by our investigations.