Ultra-large dipole moment organic cations derived 3D/2D p–n heterojunction for high-efficiency carbon-based perovskite solar cells

Abstract

The hole transport layer (HTL)-free carbon electrode-based perovskite solar cells (C-PSCs) possess promising commercial application potential due to their fascinating advantages of low cost and high stability. However, the large energy level mismatch between perovskite and carbon electrodes seriously restricts the photovoltaic performance. 3D/2D perovskite heterostructures have been widely adopted to regulate energy level alignment, whereas achieving a large built-in electric field (V_bi) is still a great challenge. Herein, we propose molecular dipole moment engineering to regulate the interface energy levels and V_bi of 3D/2D perovskite heterojunctions. Experimental and theoretical results demonstrate that an organic cation with ultra-large dipole moment significantly improves the work function of 2D perovskites, resulting in the formation of p-type 2D perovskites. Besides, an ultra-thick (>200 nm) 2D perovskite layer is constructed on the surface of the 3D perovskite film. This results in the construction of 3D/2D p–n junctions, significantly enhancing the V_bi. As a result, the formed powerful 3D/2D heterojunction not only effectively passivates the defect states, but also markedly promotes the extraction of photogenerated holes. The devices achieve a new record efficiency of 20.08% (certified 19.6%) for HTL-free C-PSCs. The unencapsulated devices maintain 96% of the initial value after operating for 1000 h at maximum power point.