Solution-processed polycrystalline mixed halide perovskite solar cells have already achieved excellent power conversion efficiencies. However, severe thin film heterogeneity exists ubiquitously across multiple length scales, including composition, lattice structure, and defects, which significantly impacts device lifetime. So far, the molecular assembly during lattice transformation in thin film growth remains not fully understood.

Chen Qi et al. from Beijing Institute of Technology revealed the mechanism of topological chemical assembly. The authors found that introducing intermediates enables the crystal to grow along different coherent interfaces. The authors obtained a (001)-oriented film that possesses minimized lattice heterogeneity, microstructural defects, and electronic disorder.

In addition, the corresponding inverted devices maintained over 95% of their initial power conversion efficiency (PCE) after 500 hours of operation (AM 1.5G, one sun illumination). This work uncovers the potential mechanism of controlling perovskite crystal synthesis.