Surface trap–mediated nonradiative charge recombination is a major limit to achieving high-efficiency metal-halide perovskite photovoltaics. The ionic character of perovskite lattice has enabled molecular defect passivation approaches through interaction between functional groups and defects. However, a lack of in-depth understanding of how the molecular configuration influences the passivation effectiveness is a challenge to rational molecule design. Here, the chemical environment of a functional group that is activated for defect passivation was systematically investigated with theophylline, caffeine, and theobromine. When N-H and C=O were in an optimal configuration in the molecule, hydrogen-bond formation between N-H and I (iodine) assisted the primary C=O binding with the antisite Pb (lead) defect to maximize surface-defect binding. A stabilized power conversion efficiency of 22.6% of photovoltaic device was demonstrated with theophylline treatment.
Effective management of the insulating ligands is prerequisite for achieving good electrical coupling between colloidal quantum dots (CQDs) and, thus, highperformance solar cells. Here, we developed a rationally designed post-synthetic process for effective control of ligand density on organic-inorganic hybrid formamidinium lead triiodide (FAPbI 3) perovskite CQDs. The resulting FAPbI 3 CQD solar cells demonstrated power-conversion efficiency of 8.38% with stability superior to that of bulk FAPbI 3 devices.
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