The power conversion efficiencies (PCEs) of organolead halide perovskite solar cells have leaped from a pioneering value of 3.8 % to a series of certified values exceeding 20 % in the past 5 years. The key to high-performance perovskite solar cells is the realization of excellent crystallinity and micro-sized grains in the perovskite active layers. Recently, a two-step deposition method incorporated with intramolecular exchange process has been demonstrated to prepare high quality densely-packed formamidinium lead iodide (FAPbI3) perovskite grains. The morphology of the first layer, PbI2, plays a crucial on the crystal growth of perovskites after depositing the second layer, CH3NH3I. However, there is still lack of effective controls over the film morphology by conventional spin coating or drop casting processes due to strong flow instabilities during evaporation. Controlled evaporation induced self-assembly (CESA) has been widely utilized to regulate solvent evaporation process, thereby entailing highly-ordered deposition structures of various nonvolatile nanomaterials (i.e., DNA, micelles, colloidal nanoparticles, and block copolymers). As a movable CESA, flow-enabled self-assembly offers a promising route to controlling the formation of highly-ordered continuous nanostructures in large area. Herein, we report a facile strategy of fabricating large-grain sized organolead halide perovskite thin films by FESA in ambient condition, resulting in high-efficiency perovskite solar cells with long-term stability in air. Compared with conventional spin-coating process, FESA enables tunable parameters (e.g., concentration, temperature, geometry) to optimize the film formation of perovskite crystals in large area, thereby providing a more reproducible procedure as well as a pathway to exploring the structure-performance relationship of perovskite solar cells.

Organolead halide perovskite solar cells enabled by flow-enabled self-assembly

251st National Meeting (2016)

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