Ligand-mediated suppression of Ostwald ripening enables low-temperature sol-gel ZnO for efficient inverted flexible organic photovoltaics

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Chinese explanation / 中文解读

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Original abstract

Inverted flexible organic solar cells (F-OSCs) require low-temperature processing, but sol-gel ZnO as widely used electron transport layers (ETLs) demand high-temperature annealing above 150 oC, limiting incompatibility with plastic substrates. Here we introduce a ligand-directed strategy using N,N-dimethylethylenediamine (DMEN) that stabilizes the precursor as discrete Zn–O–Zn clusters, suppresses Ostwald ripening, and lowers the crystallization barrier, thus enabling high-quality ZnO ETLs at remarkably low temperatures (<90 oC). DMEN-ZnO achieves >17.3% efficiency with PM6:BTP-eC9, matching the performance of ethanolamine-ZnO processed at 200 oC. With an ultrathin LiF passivation layer, champion efficiencies of 19.13% (rigid) and 18.01% (flexible) are obtained in the D18:BTP-eC9 system. Flexible devices retain 96% of initial performance after 3000 bending cycles at 4.5 mm radius. This work provides insight into precursor chemistry and crystallization control, establishes a low-temperature, scalable route for ZnO ETLs that bridges the gap between efficiency-flexibility in OSCs. Solar cells using sol-gel ZnO are typically limited by the high temperature processing that is incompatible with plastic substrates. Here, the authors present a ligand-directed strategy using DMEN hat stabilizes the precursor, thus producing high quality ZnO at 70-90 °C for rigid and flexible solar cells.

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