Nano‐Space Confinement Crystal Growth Boosted Hole Extraction in Carbon‐Based CsPbI3 Perovskite Solar Cells

Carbon‐based CsPbI3 perovskite solar cells (C‐PSCs) have shown a great promising due to its excellent chemical stability. However, the low hole selectivity and inefficient charge separation at the perovskite/carbon interface suppress their photovoltaic performance. Introducing a low‐dimensional (LD) perovskite structure is anticipated to address the issue but the randomly grown LD perovskite crystals would considerably increase the surface roughness, which not only weakens interface contact for inhibiting hole extraction but also increases the charge transporting length in LD perovskite. Herein, COMSOL Multiphysics simulation is first explored to establish the relation of the LD perovskite structure with the device performance, which suggests that a p‐type and thin LD perovskite capping layer with high coverage is favorable for device performance. To verify the simulation results, a nano‐space confinement (NSC) strategy is proposed to inhibit the vertical growth of 2D Cs2PbI2Cl2 perovskite plates for promoting in‐plane growth, during which a polymethyl methacrylate (PMMA) layer is pre‐covered on the Cs2PbI2Cl2 nuclear before their growth. Consequently, a well‐covered p‐type Cs2PbI2Cl2 capping layer is deposited on n‐type CsPbI3 perovskite layer, which significantly increases the hole selectivity and enhances charge separation for promoting the efficiency of C‐PSCs to 18.23% with an ultra‐high VOC of 1.161 V.