Perylene derivatives are a class of organic aromatic molecules, which possess large molar absorptivity, high quantum yields (QYs) in the monomer state, and tunable optical properties and thus have attracted much attention for diverse applications, such as photodetectors, solar cells, bioimaging, and luminescent solar concentrators (LSCs). [1][2][3][4][5][6][7][8] The photophysical properties can be regulated in several ways, such as by introducing the substituents at different sites for desired applications. [9,10] In addition, they can be also controlled via intermolecular interactions, for example, by the formation of dimers or aggregates through noncovalent interactions, such as πÀπ stacking and hydrogen bonding. [11][12][13] The monomer species of perylene dyes dispersed in organic solvent typically exhibited near-unity QYs. Unfortunately, when transferred to solid state (required for most optoelectronic applications), their QYs would be significantly reduced by severe aggregation-caused quenching (ACQ) via strong πÀπ stacking, for example, down to 7À12% for neat films. [14] Two different ways can be used to mitigate the ACQ effect, including functionalization with bulky substituents and introduction of a compatible solid matrix. [15][16][17][18][19][20][21][22][23][24] For example, Zhang et al, addressed the ACQ issue by functionalizing the perylene diimides with bay-position substitution. [25] Such substitution can slightly mitigate intermolecular πÀπ stacking by steric hindrance, still suffering from

The low stability of perovskite solar cells is the limiting factor for their commercialization, which is largely affected by defects originating from crystallographic distortions and interface formation in solution-processed lead halide perovskite thin films. Herein, urea and thiourea small molecules are used as dopants to synergistically increase the power conversion efficiency (PCE) and stability of the perovskite solar cells by regulating the morphology and crystallinity of the perovskite thin films. X-ray diffraction, atomic force microscopy, Fourier-transform infrared spectroscopy, transmittance spectra, day-dependent photoluminescence (PL), and Raman scattering spectra are used to briefly compare the crystal growth and defect passivation mechanisms of urea and thiourea small molecules. The PCE of thiourea-doped perovskite solar cells gradually increases as a function of storage duration, from 12.12 ± 0.15% to 18.38 ± 89% in 40 days. Day-dependent PL and Raman scattering spectra reveal that the crystallinity of the thiourea-doped perovskite thin film improves over time, resulting in slow passivation from thiourea small molecules and consequently an improvement in device performance.