Revisiting the Impact of Interfacial Transport Layers on Organic Bulk Heterojunction Systems

Abstract

The utilization of interfacial transport layers is critically important for extensively elaborating organic photovoltaic efficiencies. Despite some fundamental knowledge regarding their electrical and optical properties, a full realization of their impact on photoactive layers is still lacking. In this work, we report a new insight into the impact of the interfacial transport layers on physical properties of an organic bulk heterojunction (BHJ) system comprising ITO(glass)/PEDOT:PSS/PIDTDTQx:PC70BM/PFN/Al. A combination of multiple measurements was performed either at steady states or at working conditions aiming to deeply understand the role of the interfacial transport layers in the organic BHJ photovoltaics. Experimental results validated our assumption that the optoelectronic properties of the organic blends, such as PIDTDTQx:PC70BM, can be remarkably influenced due to the presence of the electron/hole transport layers. We have looked into this issue by examining the organic blend PIDTDTQx:PC70BM-based BHJ photovoltaic devices from the interfacial trap-related density of states, electron–hole recombination resistance (Rrecomb), recombination lifetime (τrecomb), excitons lifetime (τ), photoinduced electrical polarization, energetic disorder characteristic, and magneto-photocurrent, respectively. Our concept should guide people to reconsider the critical role of the interfacial transport layer in the organic BHJ system, in particular to compensate with two controversial assumptions: (i) properties of the organic blend are nearly unaltered due to the presence of the interfacial transport layers, and (ii) they mainly facilitate the charge carrier extraction and injection. By highlighting the factors that eliminate the performance of the organic photovoltaics, we thus believe this work offers scientifically valuable information for device physicists because the optoelectronic, dielectric, and electronic structure properties of the organic blend are firmly bound to the presence of the interfacial transport layer.