Deterministic Fabrication of 2D/3D Heterojunction for Efficient and Stable Carbon-Based Hole-Transport-Layer-Free Perovskite Solar Cells

The incorporation of two-dimensional (2D) perovskite onto the three-dimensional (3D) perovskite structure presents an effective approach for passivating surface defects, optimizing energy level alignment, and stabilizing the active layers in perovskite solar cells (PSCs), thereby facilitating the realization of highly efficient and stable devices. However, it remains a formidable challenge to achieve precise composition and controllable structure of 2D/3D perovskite heterojunctions through solution processes. Additionally, uncontrolled cation exchange among organic constituents poses challenges in controlling the precise positioning and thickness of 2D perovskite phases, resulting in mismatched band alignments and unfavorable recombination. In this study, the fabrication of deterministic 2D/3D perovskite heterojunctions is achieved using a solid-phase hot-pressing deposition method, wherein the investigation focuses on their growth mechanisms, energy level alignments, and film stabilities. The results demonstrate that a uniform 2D perovskite layer was formed on the surface of 3D perovskite layer under the influence of applied pressure and heat. The resulting 2D/3D perovskite heterojunction forms a favorable energy alignment with the adjacent carbon electrode, thereby effectively enhancing charge extraction and suppressing losses due to interface recombination. As a result, the carbon-based hole-transport-layer-free (HTL-free) PSCs based on a 2D/3D perovskite heterojunction demonstrate an outstanding power conversion efficiency (PCE) of 16.09%. Moreover, the incorporation of a 2D perovskite layer enhances hydrophobicity, leading to significant improvements in film stability. Therefore, this study presents a facile and practical approach for the fabrication of deterministic 2D/3D perovskite heterojunctions, offering potential opportunities for cost reduction and performance enhanced for PSCs.