Emerging Strategies toward Mechanically Robust Organic Photovoltaics: Focus on Active Layer

Abstract

The biggest advantages of OPV to complement with inorganic photovoltaics in the future lie in the flexibility of organic active-layer materials, which not only enables the roll-to-roll processing [21] but also allows the integration of OPV devices in many form factors inaccessible by inorganic devices, such as clothing, portable electronics, agricultural greenhouses, biomedical applications, and extremely flexible and stretchable devices. [22][23][24][25][26][27][28][29][30][31][32][33] For instance, Someya et al. [34,35] demonstrated washable, stretchable, and lightweight OPVs with a PCE of 7.9% as textile-compatible power sources, which can be used as a long-term power source for wearables, electronic textiles as well as sensors for the Internet of Things. Mechanical stability is required not only for the portable applications mentioned above, which must accommodate strain as a function of operation, but also enable the solar module to withstand the impact, vibration, and other stresses that occur during manufacturing, transportation, and utility-scale applications. For example, to withstand different sorts of mechanical stresses during the coating process (e.g., roll-to-roll printing), a consistent degree of stretchability and flexibility is necessary. Furthermore, steady performance under constant mechanical stress should be ensured to meet the real-world applications of portable and wearable devices. However, the mechanical reliability of OPVs has received far less attention than other aspects of stress and is far from adequate for commercial application.Conjugated polymers for the OPV active layer have intrinsic mechanical deformability, which sets them apart from their inorganic counterparts. The upper limit of PCE and mechanical stability of the overall OPV device would be determined by an appropriate active layer with optimized morphology. In fact, the active-layer system of the state-of-the-art OPVs with PCEs of ≈20% can hardly meet the demands of flexible electronics. Recently, there has been a growing awareness of the importance of mechanical robustness; scientists have reported a variety of conceptual research aimed at mechanically reliable OPVs, making it a hot issue in the field of OPVs.This perspective first classifies the working scenarios of flexible OPVs: static condition (low-frequency large deformations) and dynamic condition (high-frequency small deformations), and then discusses the corresponding strategies toward mechanically robust active layer: improve ductility, strengthen donor/acceptor interfaces, and restrain molecule migration. Afterward, the current achievements in improving the mechanical robustness of active layers are summarized in the aspects Mechanical stability of organic photovoltaics (OPVs) is required not just for portable applications, which must accommodate strain as a function of operation, but also for manufacturing, transportation, and utility-scale applications. However, the mechanical reliability of OPVs is often disregarded compared with other stress (thermal, oxyg...

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