High-Performance Indoor Organic Photovoltaics Enabled by Screening Multiple Cases of Electron Acceptors

Abstract

Recently, indoor organic photovoltaics (IOPV) has gradually entered people's field of vision due to the elevated demands of Internet of Things (IoTs). However, the mismatch between the absorption spectrum of organic photovoltaic materials and the emission spectrum of indoor light sources limit the output power of IOPV, which do not meet the requirement of IoTs. In order to clarify this issue, we fabricated three different OPVs by screening three electron acceptors with different absorption spectrum, PC71BM, N2200, and PYF-T, to match with a high-performance wide-bandgap electron-donating polymer containing imide-functionalized benzotriazole units (PTzBI-oF). PYF-T-based device performed best under AM 1.5G sunlight illumination, while PC71BM-based device performed best under indoor LED illumination, which can be attributed to the suppressed dark current (JD) and significantly enhanced parallel resistance (RP) of PC71BM-based device. We systematically analyzed and understood the interrelationship between the absorption spectrum, JD, RP, phase separation morphology, crystalline and orientation behavior, and photovoltaic performance of IOPVs, proving that an extremely low JD and sufficiently large RP is crucial for fabricating efficient IOPVs. The JD suppression can be achieved by morphology regulation of the active layer, where the donor-acceptor pair needs to display a suitable phase separation scale, strong crystallinity, and ideal molecular orientation for the donor-acceptor interface. Our work can provide guidance for the future design of donor-acceptor pairs for efficient IOPV, and promote the further application of IOPV.

Keywords: indoor organic photovoltaics, electron acceptors, dark current, parallel resistance