Recently perovskite solar cells (PSCs), as photoelectric conversion devices, exhibit excellent power conversion efficiency (PCE) and low-processing cost, and have become one of the most promising devices to replace conventional silicon-based solar cells and address current pressing energy issues. Among them, the flexible PSCs are especially more widely applicable and may propel the rapid advancements of wearable electronics, causing a significant paradigm shift in consumer electronics. Current flexible PSCs use non-biodegradable petroleum-based polymer substrates, discarding of which will aggravate “white pollution”. Therefore, development of green, biodegradable and low-cost flexible substrates will provide a great alternative to flexible PSCs. Here we have developed transparent nanocellulose paper (NCP) with coating of acrylic resin as substrates to fabricate flexible PSCs, which are biodegradable and easily disposable. The PCE of these NCP-based PSCs reached 4.25%, while the power per weight (the ratio of power to device weight) was as high as 0.56 W g–1. The flexible PSCs also showed good stability, retaining >80% of original efficiency after 50 times of bending. The NCP-based substrates can also be applied to other electronic systems, which may prosper next-generation green flexible electronics.

Interfacial engineering is a simple and effective strategy that can improve the photovoltaic performance in organic-inorganic perovskite solar cells (PSCs). Herein, a dopamine (DA) self-assembled monolayer (SAM) was introduced on the top of the SnO electron transporting layer (ETL) to modify the SnO/perovskite interface. The processing temperature of the present devices is around 150 °C, and the power conversion efficiency of the PSCs was significantly improved to 16.65% compared to that of the device without modification (14.05%). Such enhancement in efficiency is mainly attributed to the improved quality of perovskite films by improving the affinity of the SnO ETL, thus leading to better carrier transport and low charge recombination at the SnO/perovskite interface. Moreover, the modified device by the DA SAM exhibited enhanced stability compared to the device without modification. Our results suggest that the introduction of the DA SAM on the ETL/perovskite interface is a promising method for highly efficient and stable PSCs.

The use of a synergistic additive NH4SCN in constructing organic–inorganic hybrid perovskite films improves the quality of perovskite films, enhances the stability, and promotes the device efficiency.