Oriented Low-n Ruddlesden-Popper Formamidinium-Based Perovskite for Efficient and Air Stable Solar Cells

摘要

The relatively lower crystallinity and random orientation of quantum wellstructures hinder carrier transport and limit the performance of formamidinium(FA) based low-n 2D perovskite devices. In this work, the crystallizationand quantum well orientation are fine tuned to achieve efficient low-n FAbased Ruddlesden–Popper perovskite solar cells. The effects of different ionicadditives on the crystallization, orientation, and photovoltaic performanceof FA based low-n 2D perovskites are comparatively investigated. It is foundthat NH_4~+ and SCN? can significantly retard the heterogeneous crystallizationof low-n phases in the intermediate state, and drive the templated growth ofquantum well structure with vertical orientation. The optimized photovoltaicdevice based on (BA)_2(FA)_3Pb_4I_(13) achieved a power conversion efficiency(PCE) of 18.14%, setting the highest record for FA-based low-n 2D perovskitesolar cells as far as it is known (average n = 4). The unencapsulated deviceexhibited excellent stability and maintained 93.3% of its original PCE at 85 ℃,and 86.3% at 1 Sun illumination after 720 h in humid ambient condition.