P-Type Doping of Mixed Tin-Lead Halide Perovskites Using Electron Transfer to Mo(tfd-COCF3)3 and F4TCNQ

Mixed tin-lead halide perovskites are emerging as promising candidates to address the toxicity issues of lead-based perovskites and to provide additional bandgap tunability for optoelectronic applications. Electron-transfer doping offers a prospective pathway to modulate electronic properties of metal-halide perovskites, while not disturbing the underlying crystal structure. However, limited research exists comparing molecular dopants for these systems. Our study investigates the p-type electron-transfer doping of the mixed tin-lead halide perovskite MAPb0.5Sn0.5I3 (MA = methylammonium) using a sequential deposition approach (perovskite film followed by dopant incorporation) and the molecular dopants F4TCNQ and Mo(tfd-COCF3)3. Up to 3 orders of magnitude higher carrier density and up to 2 orders of magnitude greater conductivity are achieved relative to the undoped samples, with F4TCNQ and Mo(tfd-COCF3)3 demonstrating similar doping efficiencies (associated with the ratio of mobile charges added to the number of dopant molecules incorporated) of 0.031(3) % and 0.024(3) %, respectively. Differences in the doping effectiveness for a given molarity doping solution likely follow from variations in dopant incorporation within the film during the spin coating deposition step.