One-step spin-coating solution deposition was reported as an excellent processing method in perovskite solar cells (PSCs). Antisolvent treatment has been demonstrated to significantly enhance the power conversion efficiency (PCE) of PSCs owing to the formation of high-quality perovskite crystals and passivation of defects. In this article, we alter different antisolvents in solution deposition process, i.e., chlorobenzene, toluene, and diethyl ether, combined with different measurements of scanning electron microscopy, atomic force microscopy, X-ray diffraction, time-resolved photoluminescence, and UV–vis absorption spectrum (UV–vis) to investigate the evolution of perovskite thin films. These results illustrate that a smooth and compact perovskite layer by antisolvent treatment is beneficial to enhancing device performance. A high coverage, large crystal size and smooth Cs
0.15
FA
0.85
PbI
3
thin film with a long carrier lifetime attained via antisolvent treatment is utilized to fabricate an inverted planar heterojunction solar cell, which exhibits PCE more than 15%.
Summary Dissociation of organic molecules is one critical factor leading to degradation of perovskite solar cells. The much-improved thermal stability of formamidinium (FA) can significantly reduce molecular dissociation; however, FA-based perovskite suffers from high defect density, which affects efficiency and long-term stability. In this work, based on a precise ion-exchange reaction at the grain surface, we fabricate a Cs 0.15 FA 0.85 PbI 3 /Cs x FA 1-x PbI 3 heterostructure with a Cs-rich Cs x FA 1-x PbI 3 quasi-shell structure. The Cs-rich inorganic structure on the perovskite surface increases defect formation energy and reduces defect density, leading to a power conversion efficiency of 20.7%. The encapsulated device maintains 95% of its initial efficiency after 1,000 h of continuous operation, corresponding to a calculated lifetime approaching 2 years. The device can operate at 60°C for 250 h and at 85°C for over 3,000 min, which is one of the best operational stabilities for Cs x FA 1-x PbI 3 -based devices.
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