Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP27)
Publication date: 22nd October 2026
Interfacial energy offsets play a decisive role in governing the device performance of organic photovoltaic (OPV) and perovskite solar cells. In this talk, I will discuss how interfacial energy offsets primarily dictate the open-circuit voltage (VOC) in these photovoltaics through several of our recent studies.
In perovskite solar cells, energy offsets between the perovskite photoactive layer and charge transporting layers induce significant charge recombination. For representative mixed-cation lead-based perovskite cells, aging for several days is widely known to enhance VOC. We demonstrate that immediately following fabrication, the hole-transporting material spiro-OMeTAD remains in a neutral molecular state with a shallow HOMO level. This results in a large energy offset relative to the perovskite valence band, rendering surface recombination dominant. Upon aging, spiro-OMeTAD molecules are oxidized into dication species, effectively reducing the energy offset, suppressing surface recombination, and boosting VOC.
In OPVs, the donor/acceptor (D/A) heterojunction energy offset governs VOC. We found that even among donor conjugated polymers with identical backbone structures, subtle variations in side-chain configurations alter local packing structures, resulting in distinct D/A interfacial energy offsets and hence VOC values. Furthermore, a comparison of hole-transporting layers—such as the conductive polymer PEDOT:PSS versus the surface-modifying molecule Br-2PACz—demonstrates marked differences in interfacial recombination dynamics and resulting VOC.
These insights underscore the profound influence of heterojunction energy offsets on VOC in both OPV and perovskite devices. Finally, we discuss the exciton binding energy of Y6 molecules utilized in single-component OPVs, where charge carriers are generated even in the absence of D/A heterojunction interfaces.
Acknowledgments
This work was supported by JSPS KAKENHI (Grant Nos. JP21H04692, JP22K19062), the JST MIRAI projects (Grant Nos. JPMJMI20E2, JPMJMI22E2), the JST ALCA-Next Program (Grant No. JPMJAN25G1).
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