Enhancement of photoelectric performance for CsPbI2Br solar cells by the synergistic effect of binary additives

CsPbI2Br-based perovskite solar cells (PSCs) have attracted much attention because of their excellent phase stability and appropriate bandgap. However, numerous defects of undercoordinated ions or mobile species are the sites of carrier nonradiative recombination, causing a low power conversion efficiency (PCE). In this work, NaCl and nitrogen-doped graphene quantum dots (N-GQDs) as binary additives are introduced into perovskite precursor to obtain high-quality photoactive films. Chloride ion (Cl−) is incorporated into perovskite due to the same physical and chemical properties as bromine (Br−), that align the energy level of CsPbI2Br, decrease the energy barrier between perovskite and P3HT to promote carrier transport and extraction, hence result in the reduced energy loss. Meanwhile, because of its good conductivity, N-GQDs at grain boundaries can rapidly conduct photogenerated electrons to SnO2, suppressing carrier recombination at grain boundaries. Furthermore, the trap state density of the CsPbI2Br film with binary additives is reduced, which could prolong the carrier lifetime, and improve surface morphology. As a result, a PCE of 15.37% for CsPbI2Br PSCs with binary additives is obtained，which shows ∼22.76% relative increment compare with the pristine PSCs. Therefore, a simple and convenient optimization strategy of binary additives for PSCs is proposed in this work.