Tailoring carrier management through a multifunctional additive for efficient perovskite/organic tandem solar cells

The wide bandgap perovskite solar cells (PSCs) are promising candidates for high-efficiency tandem photovoltaics. However, these devices encounter challenges arising from defects within the perovskite lattice and at interfaces, which lead to non-radiative recombination and voltage losses. To address these issues, we have developed a synergistic approach that combines bulk passivation using l-cystine dihydrochloride as an additive with subsequent surface passivation treatments. This compound effectively passivates Pb2+ and halide defects through its carbonyl and amine functional groups. Both experimental and simulation results demonstrate that l-cystine dihydrochloride effectively reduces trap states, retards nucleation kinetics, promotes grain growth, and enhances crystallinity. Consequently, the device [FA0.8Cs0.2Pb(I0.6Br0.4)3, energy gap: 1.77 eV] incorporating l-cystine dihydrochloride achieved a power conversion efficiency (PCE) of approximately 16.00%, which was further increased to 17.03% with an additional octylammonium iodide surface passivation. Expanding our approach, we have fabricated the wide bandgap semitransparent device, yielding a PCE of 15.62%. When integrated with narrow-bandgap organic solar cells in four-terminal (4T) perovskite/organic tandem solar cells, a remarkable efficiency of 23.14% was attained. This strategy effectively improves the performance of wide bandgap PSCs, which exhibit great potential in advancing perovskite/organic photovoltaic technologies.