Donor-acceptor interfacial dipole polarization for efficient and stable thick-film organic photovoltaics

Minimizing photocarrier trapping is essential for developing high-performance organic solar cells (OSCs) with thick active layers. Herein, a synergistic strategy combining interfacial dipole polarization with donor-acceptor dilution is presented to achieve this aim. This strategy first entails the additional deposition of an acceptor, AITC with a large dipole moment, between the donor (PM6) and acceptor (L8-BO) layers. The donor-acceptor interfacial dipole polarization induced by AITC creates a permanent polarization field that aligns positively with the direction of the built-in electric field (Vbi), yielding a significant increase in Vbi. Meanwhile, the lifetime of photogenerated excitons in L8-BO is substantially prolonged due to suppressed internal conversion through intermolecular vibrational coupling between L8-BO and AITC. The diluted donor-acceptor heterojunction is subsequently constructed with the PM6 layer containing traces of acceptor N3 and the L8-BO layer with traces of donor DRTB-T-C4 to improve structural order and restrain molecule distortion in the excited state. An ideal gradient phase separation morphology with high driving force and long lifetime for excitonic and electronic excitations has been reshaped, alleviating vertical photocarrier trapping pathways. Accordingly, 300-nm-thick target cells deliver a promising efficiency of 18.20 % and exhibit superior stability. These findings could inspire the future design of high-efficiency thickness-insensitive OSCs.