Dopant-free polymer/2D/3D perovskite solar cells with high stability

Dopant-free hole transporting materials (HTMs) are promising to tackle the stability issue of perovskite solar cells (PSCs) compared to traditional ones requiring hygroscopic additives. In addition to developing more dopant-free HTMs and increasing their hole extraction/transport ability, interfacial issues between perovskite and dopantfree HTM also remarkably impact on the PSC performance, which, however, have been less concerned. Herein, we introduce a 2D perovskite layer to the interface of 3D perovskite and a dopant-free polymeric HTM to improve the device efficiency and stability. The 2D perovskite layer can increase hole transports by offering a gradient energy-level alignment, decrease defects density, and improve contact at the interface, which are more efficiently when the 2D perovskite is prepared from a fluorine-containing organic cation. Accordingly, a device efficiency of 20.5% is obtained, quite impressive for dopant-free HTM-based 2D-3D PSCs. In particular, these devices without encapsulation exhibit excellent stability under high humidity (85%), heating (80 degrees C), or light illumination (1-sun), ascribed to double protections from both 2D perovskite layer and dopant-free polymer. This work offers a promising method to enhance the efficiency and stability of dopant-free HTM-based PSCs by introducing a 2D perovskite layer at the interface.