Plant Sunscreen and Co(II)/(III) Porphyrins for UV-Resistant and Thermally Stable Perovskite Solar Cells: From Natural to Artificial.

The poor UV, thermal, and interfacial stability of perovskite solar cells (PSCs) makes it highly challenging for their technological application, and has drawn increasing attention to resolving the above issues. In nature, plants generally sustain long exposure to UV illumination without damage, which is attributed to the presence of the organic materials acting as sunscreens. Inspired by the natural phenomenon, a natural plant sunscreen, sinapoyl malate, an ester derivative of sinapic acid, is employed to modify the surface of electron transport materials (ETMs). The interfacial modification successfully resolved the UV stability and reduced the poor interfacial contact between ETM and perovskite. The best efficiency of fabricated PSCs is up to 19.6%. Furthermore, we employed a mixture of Co(II) and Co(III)-based porphyrin compounds containing the excellent Co(II)/Co(III) redox couple to substitute the commonly used hole transport material, 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spiro-bifluorene (spiro-OMeTAD), to resolve the thermal degradation of PSCs noted at and above 80 °C that originates from ion diffusion of I- and CH3 NH3+ (MA+ ) ions from perovskite into spiro-OMeTAD. Finally, the stable PSCs with the best efficiency up to 20.5% are successfully fabricated.