Defect management and crystallization regulation for high-efficiency carbon-based printable mesoscopic perovskite solar cells via a single organic small molecule

High-quality perovskite films are crucial for achieving efficient carbon-based printable mesoscopic perovskite solar cells (MPSCs). However, rapid crystallization leads to poor film quality and the formation of defects, resulting in severe non-radiative recombination that hinders the improvement of device performance. In this work, an organic small molecule, dicyandiamide (DCDA), with multifunctional groups was incorporated into the perovskite precursor solution to concurrently regulate crystallization and manage defects in the perovskite in the mesoporous scaffold, and high performance MPSCs were obtained. Due to the robust interactions of the –CN and –CN groups in DCDA with un-coordinated Pb²⁺, and/or FA⁺/MA⁺ via hydrogen bonding, coupled with the –NH₂ groups of DCDA forming hydrogen bonding or electrostatic interactions with halide anions to inhibit ion migration, the defects were passivated. The introduction of DCDA effectively retarded nucleation and grain growth, and significantly reduced the film formation rate. Thus, perovskite films with larger grain sizes, preferred orientation, and lower trap state density were obtained, thereby greatly suppressing non-radiative recombination. As a result, the average power conversion efficiency (PCE) of MPSCs treated with DCDA was improved from 17.15 ± 0.48% to 18.75 ± 0.42%, and a champion PCE of 19.12% was obtained. Meanwhile, the PCE of unpackaged MPSC devices still remained at 94.00% of the initial efficiency when stored in an air environment after 103 days, demonstrating excellent stability. The strategy facilitates a deeper understanding of perovskite crystallization in printable MPSCs.