Surface-functionalized hole-selective monolayer for high efficiency single-junction wide-bandgap and monolithic tandem perovskite solar cells

Carbazole moiety-based 2PACz([2-(9H-carbazol-9-yl)ethyl]phosphonic acid)self-assembled monolayers(SAMs)are excellent hole-selective contact(HSC)materials with abilities to excel the charge-transferdynamics of perovskite solar cells(PSCs).Herein,we report a facile but powerful method to functionalize the surface of 2PACz-SAM,by which reproducible,highly stable,high-efficiency wide-bandgap PSCs can be obtained.The 2PACz surface treatment with various donor number solvents improves assembly of 2PACz-SAM and leave residual surface-bound solvent molecules on 2PACz-SAM,which increases perovskite grain size,retards halide segregation,and accelerates hole extraction.The surface functionalization achieves a high power conversion efficiency(PCE)of 17.62%for a single-junction wide-bandgap(~1.77 e V)PSC.We also demonstrate a monolithic all-perovskite tandem solar cell using surfaceengineered HSC,showing high PCE of 24.66%with large open-circuit voltage of 2.008 V and high fillfactor of 81.45%.Our results suggest this simple approach can further improve the tandem device,when coupled with a high-performance narrow-bandgap sub-cell.

High-throughput compositional mapping of triple-cation tin-lead perovskites for high-efficiency solar cells

Mixed tin-ead perovskites suffer from structural instability and rapid tin oxidation;thus,the investigation of their optimal composition ranges is important to address these inherent weaknesses.The critical role of triple cations in mixed Sn–Pb iodides is studied by performing a wide range of compositional screenings over mechanochemically synthesized bulk and solution-processed thin films.A ternary phase map of FA(Sn_(0.6)Pb_(0.4))I_(3),MA(Sn_(0.6)Pb_(0.4))I_(3),and Cs(Sn_(0.6)Pb_(0.4))I_(3)is formed,and a promising composition window of(FA_(0.6-x)MA_(0.4)Cs_(x))Sn_(0.6)Pb_(0.4)I_(3)(0≤x≤0.1)is demonstrated through phase,photoluminescence,and stability evaluations.Solar cell performance and chemical stability across the targeted compositional space are investigated,and FA_(0.55)MA_(0.4)Cs_(0.05)Sn_(0.6)Pb_(0.4)I_(3)with strain-relaxed lattices,reduced defect densities,and improved oxidation stability is demonstrated.The inverted perovskite solar cells with the optimal composition demonstrate a power conversion efficiency of over 22%with an open-circuit voltage of 0.867 V,which corresponds to voltage loss of 0.363 V,promising for the development of narrow-bandgap perovskite solar cells.