Effect of concomitant anti-solvent engineering on perovskite grain growth and its high efficiency solar cells

The grain boundaries and interface properties in the active layers of perovskite solar cells (PSCs) are important factors affecting the performances of the devices. In this work, a simple and fast concomitant annealing process is established by inducing the secondary growth of the grains using the anti-solvento-dichlorobenzene (o-PhCl2) or chlorobenzene (PhCl) to suppress the volatilization of solvent molecules during the FA(0.80)MA(0.15)Cs(0.05)Pb(I0.85Br0.15)(3)(FA, CH5N2+, formamidine; MA, CH3NH3+, methylamine) film annealing procedure. The effects of anti-solvent molecules on the phase transformation, grain boundary fusion and morphology evolution of perovskite films are systematically investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that anti-solvent molecules can inhibit solvent evaporation in the active layers and promote crystallite dissolution and ordered secondary growth along the surfaces of large grains. That can promote the formation of large grains and the passivation of surface defects, and can be favorable for the separation and transportation of photocarriers in the active layer. Consequently, the power conversion efficiency (PCE) of PSCs can be effectively improved, with a PCE of 20.72% being achieved by a secondary growth perovskite film optimized witho-PhCl2. Moreover, the efficiency remains at 85% of its initial value after 2400 h of treatment in a natural indoor environment with a relative humidity of 45 +/- 5%.