A universal ionic liquid solvent for non-halide lead sources in perovskite solar cells

Replacing lead iodide(PbI_(2))with suitable non-halides lead source has been found to be an effective method to control crystallization and fabricate high-performance perovskite solar cells(PSCs).However,the solubility of non-halide lead sources is highly limited by traditional solvents due to the chemical interaction limitation.Here,we report a series of non-halide lead sources(e.g.,lead acetate(PbAc_(2)),lead sulfate(PbSO_(4)),lead carbonate(PbCO_(3)),lead nitrate(Pb(NO_(3))_(2)),lead formate(Pb(HCOO)_(2))and lead oxalate(PbC_(2)O_(4)))can be well dissolved in an ionic liquid solvent methylammonium acetate(MAAc).We found that the universal strong coordination of C=O with lead ion(Pb^(2+))and the formation of hydrogen bonds were observed in perovskite precursor solution.This allows the dissolution of non-halide lead salts and is able to produce perovskite film with smooth,compact,and full coverage crystal grain.The power conversion efficiency(PCE)of 14.48%,19.21%,and 20.13%in PSCs based on PbSO_(4),PbAc_(2),and PbCO_(3) was achieved,respectively,in the absence of any additives and passivation agents.This study demonstrates the universality of ionic liquid for the preparation of PSCs based on nonhalides lead sources.

Reducing surficial and interfacial defects by thiocyanate ionic liquid additive and ammonium formate passivator for efficient and stable perovskite solar cells

Organic–inorganic metal halide perovskites have attained extensive attention owing to their outstanding photovoltaic performances,but the existence of numerous defects in crystalline perovskites is still a serious constraint for the further development of perovskite solar cells(PSCs).In particular,the rapid crystallization guided by anti-solvents leads to plenty of surficial and interfacial defects in perovskite films.Herein,we report the adoption of a pseudo-halide anion based ionic liquid additive,1-butyl-3-methylimidazolium thiocyanate(BMIMSCN)for growing ternary cation(CsFAMA,where FA=formamidinium and MA=methylammonium)perovskites with large-scale crystal grains and strong preferential orientation via the enhanced Ostwald ripening.Meanwhile,a novel halide-free passivator,benzylammonium formate(BAFa),was employed as a buffering layer on the perovskite films to suppress surface-dominated charge recombination.As a result,the cooperative effects of BMIMSCN additive and BAFa passivator lead to significant enhancements on fluorescence lifetime(from 79.41 to 201.01 ns),open-circuit voltage(from 1.13 to 1.19 V),photoelectric conversion efficiency(from 18.90%to 22.33%).Moreover,the BMIMSCN/BAFa-CsFAMA PSCs demonstrated greatly improved stability against moisture and heat.This work suggests a promising strategy to improve the quality of perovskite materials via reducing the surficial and interfacial defects by the synergistic effects of lattice doping and interface engineering.