Rational Design of Ferroelectric 2D Perovskite for Improving the Efficiency of Flexible Perovskite Solar Cells Over 23.

Abstract

Despite the great progress of flexible perovskite solar cells (f-PSCs), it still faces several challenges during the homogeneous fabrication of high-quality perovskite thin films, and overcoming the insufficient exciton dissociation. To the ends, we rationally design the two-dimensional (2D) perovskite based on pyridine heterocyclic ring as the organic interlayer. Through regulating its dipole moment by attaching the ammounium cation on different positions of the pyridine ring, we succeed to realize the ferroelectricity of the 2D perovskite. We uncover that incorporation of the ferroelectric 2D material into 3D perovskite induces an increased built-in electric field (BEF), which enhances the exciton dissociation efficiency and suppresses the nonradiative recombination in the device. Moreover, the 2D seeds could assist the 3D crystallization process by forming more homogeneous and highly-oriented perovskite crystals, and releasing the tensile stress in the film. As a result, an impressive power conversion efficiency (PCE) over 23% has been achieved by the 2D/3D based f-PSCs with outstanding ambient stability. Moreover, the ferroelectric 2D perovskite shows piezoelectricity as well, which intrigues an upshifted band-bending at the ITO/perovskite interface and decreased hole transport barriers. The device thus presents higher PCE under tensile-stresses, which opens new possibilities for developing highly-efficient f-PSCs.