Transfer-Imprinting-Assisted Growth of 2D/3D Perovskite Heterojunction for Efficient and Stable Flexible Inverted Perovskite Solar Cells.

2D/3D perovskite heterostructures show great potential to boost efficiency and stability of perovskite solar cells (PSCs). Here, a solvent-free transfer-imprinting-assisted growth (TIAG) method is employed to in situ grow 2D/3D perovskite heterojunctions. The solid-state transfer of spacer cation by the TIAG process enables a spatially confined growth of the 2D perovskite interlayer with uniform morphology between the 3D perovskites and charge transport layer. Meanwhile, the pressure associated with the TIAG process promotes the crystalline orientation, which is beneficial to carrier transport. As a result, the inverted PSC achieved a PCE of 23.09% (with certified 22.93%) and maintained 90% of their initial PCE after aging at 85 °C for 1200 h or operating for 1100 h under continuous AM 1.5 illumination. Flexible inverted PSCs achieved a PCE of 21.14% with mechanical robustness by maintaining above 80% of their initial PCE after 10000 bending cycles under a 3 mm bending radius.