Bulk Heterojunction-Assisted Grain Growth for Controllable and Highly Crystalline Perovskite Films

Perovskite optoelectronic devices are being regarded as future candidates for next-generation optoelectronic devices. Device performance has been shown to be influenced by the perovskite film, which is determined by the grain size, surface roughness, and film coverage; therefore, developing controllable and highly crystalline perovskite films is pivotal for highly efficient devices. In this work, an innovative bulk heterojunction (BHJ)-assisted grain growth (BAGG) technique was developed to accurately control the quality of perovskite films. By a simple modulation of the polymer-to-PC₆₁BM ratio in the BHJ film, the transition to a complete film phase from the perovskite precursor was accurately regulated, resulting in a controllable perovskite grain growth and high-quality final perovskite film. Moreover, because the BHJ layer could seep deeply into the perovskite active layer through the grain boundaries in the BAGG process, it facilitated the interface engineering and charge transport. The perovskite solar cells containing an optimized CH₃NH₃PbI₃ film presented a high efficiency of 18.38% and fill factor of 83.71%. The perovskite light-emitting diode that contained a nanoscale and uniform CH₃NH₃PbBr₃ film with full coverage presented enhanced emission properties with a brightness value of 1600 cd/m² at 6.0 V and a luminous efficiency of 0.56 cd/A.