Conjugated small molecule inhibiting intrinsic ion migration and enriching electron transfer channels for stable and efficient perovskite solar cells

Generally, efficient and stable perovskite solar cells (PSCs) have the following characteristics: 1) less ion migration; 2) large perovskite grain size; 3) low defect state density; 4) efficient charge transfer and inhibited carrier recombination. Herein, this work reports a facile strategy of incorporating & pi;-conjugated tetrafluoroterephthalonitrile (C8N2F4, abbreviated to CNF) into perovskite precursor solution for high-quality thin film. Surprisingly, the & pi;-conjugated CNF molecule can realize the above characteristics at the same time. As a result, the champion PSC yields a power conversion efficiency (PCE) of 22.44% as well as a stabilized PCE of 21.77%. Further, the CNF-doped PSC (unencapsulated) retains 91.62% of its initial PCE after exposed to moist air (relative humidity: 50-80%) for 1500 h and shows excellent thermal stability (T80 > 1200 h) at 85 degrees C. The increased stability is due to the cation migration inhibition and the PbI (I site substitution by Pb) and IPb (Pb site substitution by I) defect passivation of perovskite after the incorporation of & pi;-conjugated CNF molecule. Our results can deepen the understanding of organic small molecules for potential applications in improving the device PCE and the operation and long-term stability of PSC.