Enhancing the Performance of Inverted Perovskite Solar Cells via Grain Boundary Passivation with Carbon Quantum Dots

Nonradiative recombination, the main energy loss channel for open circuit voltage (V-oc), is one of the crucial problems for achieving high power conversion efficiency (PCE) in inverted perovskite solar cells (PSCs). Usually, grain boundary passivation is considered as an effective way to reduce nonradiative recombination because the defects (uncoordinated ions) on grain boundaries are passivated. We added the hydroxyl and carbonyl functional groups containing carbon quantum dots (CQDs) into a perovskite precursor solution to passivate the uncoordinated lead ions on grain boundaries. Higher photoluminescence intensity and longer carrier lifetime were demonstrated in the perovskite film with the CQD additive. This confirmed that the addition of CQDs can reduce nonradiative recombination by grain boundary passivation. Additionally, the introduction of CQDs could increase the thickness of the perovskite film. Consequently, we achieved a champion device with a PCE of 18.24%. The device with CQDs retained 73.4% of its initial PCE after being aged for 48 h under 80% humidity in the dark at room temperature. Our findings reveal the mechanisms of how CQDs passivate the grain boundaries of perovskite, which can improve the efficiency and stability of PSCs.