Graded 2D/3D (CF3-PEA)2FA0.85MA0.15Pb2I7/FA0.85MA0.15PbI3 heterojunction for stable perovskite solar cell with an efficiency over 23.0%

The replacement of small cations with bulkier organic cations containing long alkyl chains or benzene rings to form a thin two-dimensional (2D) perovskite passivation layer on three-dimensional (3D) perovskite (2D/3D) has become a promising strategy for improving both the efficiency and stability of perovskite solar cells (PSCs). The 2D layer defines the interfacial chemistry and physics at the 2D/3D bilayer and endows the 2D/3D structure with better chemical and thermal stability. Herein, 2D/3D (CF3-PEA)(2)FA(0.85)MA(0.15)Pb(2)I(7)/FA(0.85)MA(0.15)PbI(3) planar heterojunction perovskite was produced using a facile interfacial ion exchange process. The 2D (CF3-PEA)(2)FA(0.85)MA(0.15)Pb(2)I(7) capping layer can not only passivate the FA(0.85)MA(0.15)PbI(3) film but also act as super-hydrophobic layer to inhibit water diffusion and significantly enhance the stability. The 2D capping layer can also establish a unique graded band structure at the perovskite/Spiro-OMeTAD interface and lead to p-type doping for Spiro-OMeTAD layer which is beneficial for efficient charge transport. Optimized PSCs based on this 2D/3D heterojunction yield a champion power conversion efficiency (PCE) of 23.1% and improved stability. The device maintains 84% output for 2400 h aging under ambient environmental conditions without encapsulation, and maintains 81% for 200 h under illumination with encapsulation. This work will inspire the design of more fluorinated 2D perovskite interfaces for advanced photovoltaics and beyond. (C) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

By replacing small cations with bulkier organic cations containing long alkyl chains or benzene rings to form a thin two-dimensional passivation layer on three-dimensional perovskite, the efficiency and stability of perovskite solar cells can be significantly improved. The unique structure and properties of the 2D layer create better chemical and thermal stability, leading to enhanced efficiency and durability of the PSCs.