Guanidinium-assisted crystallization modulation and reduction of open-circuit voltage deficit for efficient planar FAPbBr3 perovskite solar cells

The bromide-based perovskites with wide bandgap have attracted particular interests for the potential ability to serve as front sub-cells of monolithic all-perovskite triple junction tandem solar cells. However, non-radiative recombination induced by crystal defects could cause the massive open-circuit voltage (VOC) losses, which severely disserves the performance of bromide-based perovskite solar cells. Hence, we incorporated guanidinium bromide (GABr) to modulate crystallization and heal charged defects of FAPbBr3-based solar cells. The introduction of GABr provides a non-wetting surface and suppresses heterogeneous nucleation, leading to larger grain size. Notably, nitrogen (N) atoms from GA+ cations are in two differently charged environments, which are ionized ammonium group (–NH3+) and unsaturated N atoms in form of amine or imine group (–NH2 or = NH). Thus, GA+ cations simultaneously heal both positively and negatively charged defects through multi-reactive sites with perovskite. Consequently, introduction of GABr releases microstrain and strengthens lattice structure, further transforms the perovskite from charge-rich to charge-natural region, which comprehensively leads to suppress non-radiative recombination. As a result, the high-quality planar FAPbBr3-based device yielded a PCE of 8.92% with a champion VOC of 1.639 V, which is the highest value among FAPbBr3 solar cells up to date.