Lattice Coherency-Driven (111)-Oriented Wide Bandgap Perovskite Films

초록

Perovskite solar cells (PSCs) have exhibited astonishing progress in power conversion efficiency (PCE) along with a remarkable improvement in long-term stability. A precise control on crystal growth, however, still remains challenging, particularly for poly-crystalline perovskite films based on solution- and low temperature-processing. Here in, we introduce a simple but effective strategy to regulate the crystallographic orientation of wide bandgap perovskite films (FA0.79MA0.12Cs0.09Pb(I0.85Br0.15)3; FA = formamidinium, MA = methylammonium) by utilizing lattice coherency with seed template, where MAPbBrXCl3-X not only serves as a kinetic controller for retarding crystal growth but also performs as a seed template to reshape the thermodynamic energy cost for regulating crystal orientation along face-up (111) array by offering enthalpy-driven reduced Gibbs free energy change. Consequently, perovskite films grown with the aid of a seed template exhibit outstanding crystallinity with the preferential orientation, while a weak crystallinity with a relatively random orientation is observed from the control sample. Noticeably, devices employing the (111)-oriented ordered structure, in spite of its unfavorable charge extraction, eventually result in competitive PCEs and superior long-term stability at the elevated temperature to those of (001)-oriented ones, emphasizing the importance of a highly ordered lattice with facet control in governing the device performance.

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