image: Schematic illustration of the suppression of Sn2+ oxidation by DPPF and defects passivation by the oxidation products of DPPF.
Credit: ©Science China Press
A cooperative research team from Beijing University of Chemical Technology and Linköping University introduce a redox energy barrier management strategy to enhance the performance of narrow-bandgap tin-lead (Sn-Pb) perovskite solar cells (PerSCs). The key innovation involves using 1,1′-bis(diphenylphosphino)ferrocene (DPPF), an organometallic complex, to protect Sn²⁺ from oxidation and passivate defects in the perovskite layer.
Key Findings:
- Antioxidation Mechanism: DPPF reacts preferentially with oxygen, forming oxidation products (DPPFO and DPPFO₂) that anchor to Sn vacancies, reducing trap densities. Theoretical and experimental analyses confirm DPPF's lower energy barrier for oxygen scavenging compared to Sn²⁺.
- Defect Passivation: The oxidized DPPF products coordinate with unpaired Sn²⁺ and Pb²⁺, increasing defect formation energies and improving film quality. This results in larger grain sizes, reduced non-radiative recombination, and enhanced charge carrier mobility.
- Device Performance: The optimized inverted Sn-Pb PerSC achieves a certified power conversion efficiency (PCE) of 23.5%, with a high open-circuit voltage (VOC) of 0.89 V and a low energy loss of 0.36 eV—among the best-reported values for Sn-Pb PerSCs.
- Tandem Solar Cells: When combined with a semi-transparent wide-bandgap perovskite subcell, a four-terminal all-perovskite tandem solar cell reaches a PCE of 26.4%, demonstrating the strategy's scalability for high-efficiency multi-junction devices.
- Stability: DPPF-modified devices retain 90% of their initial PCE after 1,100 hours in nitrogen and 380 hours under illumination, showcasing superior operational and thermal stability.
This work provides a holistic approach to mitigating Sn²⁺ oxidation and defect-related losses in Sn-Pb perovskites, offering a pathway to bridge the performance gap with pure-lead perovskites and advance tandem solar cell technology.