2D perovskite-stabilized FACsPbI 3 (FA = formamidinium) perovskite solar cells were fabricated in both normaltype and inverted-type architectures. While the normal-type devices exhibited a high power conversion efficiency of 20.2%, their reproducibility was limited. On the other hand, the inverted-type devices exhibited an efficiency of 18.2% with a greater stability and higher reproducibility than those of the normal-type devices. The reduced reproducibility of the normal-type devices was associated with the crack formation on the perovskite films during a spin-coating process. The hardness of both the perovskite and the sublayer was directly linked to the crack formation. Inverted-type 2D/3D FACsPbI 3 with ozone-treated poly(triarylamine) as sublayer exhibited the highest phase stability owing to the hydrophobic nature of poly(triarylamine) and improved energy level alignment upon an ozone treatment. In addition, strong interaction between phenethylamine cations of the 2D perovskite and of the 3D FACsPbI 3 crystal at grain boundaries contributed to the high phase stability.

C60:Li@C60 hybrid n-type semiconducting films were first fabricated.

Owing to its high mobility and low sintering temperature, ZnO is a promising electron-transporting layer for flexible and tandem applications of perovskite solar cells. However, ZnO inevitably triggers the degradation of perovskite materials. Such degradation can be inhibited when ZnO films with improved stoichiometry and minimized defects are used. In this work, a high efficiency with substantial stability of ZnObased perovskite solar cells is achieved using a high-workingpressure sputtering technique. The high-working-pressure sputtering process can produce higher quality ZnO films with fewer surface defects compared with conventional sputtering or sol−gel ZnO solution processes. A power conversion efficiency of 17.3% is recorded. In addition, the stability of these devices is significantly higher than that of the conventional ZnO-based perovskite solar cells. This work showcases that ZnO can be a good candidate for the electron-transporting layer in perovskite solar cells, particularly for flexible and tandem applications when the right sputtering conditions are used.

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