Open-Air Fabricated Pseudo-Planar Heterojunction Organic Solar Cells with Improved Efficiency and Thermostability via Suppression of Interfacial Degradation

Abstract Boosting both photovoltaic performance and long-term stability is currently the main challenge for organic solar cells (OSCs). In this regard, adopting a pseudo-planar heterojunction (PPHJ) photoactive layer is a promising solution because of its favorable vertical phase distribution; however, it is subject to the limitation of donor/acceptor (D/A) interfacial degradation. Herein, polyvinylidene fluoride (PVDF) is introduced as a multifunctional donor additive, enabling the suppression of interface degradation in the PPHJ photoactive layer and thereby improving the efficiency and thermostability of devices. Specifically, the introduction of PVDF slightly enhances the molecular packing and dielectric property of the photoactive layer, leading to reduced exciton binding energy (Eb) and enhanced charge transport capability of the materials. These improvements stabilize the interfacial morphology and thus suppress interfacial degradation, including deposition-induced and aging-induced degradation. Moreover, PVDF’s hydrophobicity improves moisture tolerance, enabling reliable open-air fabrication of the photoactive layer under high humidity. As a result, the open-air fabricated OSCs achieve an impressive efficiency of 19.24% with enhanced storage stability and thermal stability, which is one of the highest efficiencies for open-air fabricated OSCs. This work highlights the importance of suppressing interfacial degradation in improving performance and stability of PPHJ OSCs and provides a promising strategy to address it.