Building Bulk Heterojunction to Enhance Hole Extraction for High-Performance Printable Carbon-Based Perovskite Solar Cells

An efficient perovskite junction is critical for the functioning of perovskite solar cells (PSCs). However, carbon-based perovskite solar cells (C-PSCs) have been plagued by the paucity of ways to construct an efficient junction between perovskite and carbon, staggering around an efficiency much lower than other state-of-the-art PSCs. Herein, a perovskite/carbon bulk heterojunction (BHJ) for C-PSCs is innovated and systematically studied. First, a two-step orthogonal solvent method is developed to deposit a series of high-quality perovskite films directly on the preformed perovskite film, allowing to manipulate compositions, band alignment, and charge transfer of the perovskite junction in a low-cost and straightforward fashion. Second, by adopting this method to a porous carbon electrode as originally motivated, fabrication of perovskite/carbon BHJ with perovskite crystals by seamlessly filling in the porous carbon film is successfully done, thus providing a high contact area of perovskite/carbon heterojunction. Such a BHJ accelerates hole collection of the carbon electrode from the perovskite layer, thus significantly boosting the performance of C-PSCs with MAPbI 3 as the active layer from 12% to over 16% with certification. The device is shown to be stable with no obvious degradation after 1700 h of continuous light soaking near the maximum power point.