After demonstration of a 23% power conversion efficiency, a high operational stability is the next most important scientific and technological challenge in perovskite solar cells (PSCs). A potential failure mechanism is tied to a bias‐induced ion migration, which causes current–voltage hysteresis and a decay in the device performance over time. Herein, alkali salts are shown to mitigate hysteresis and stabilize device performance in n‐i‐p hybrid planar PSCs. Different alkali salts of potassium chloride, iodide, and nitrate as well as sodium chloride and iodide are deposited from aqueous solution onto the n‐type contact, based on SnO2, prior to deposition of the perovskite absorber Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3. Introduction of potassium‐based alkali salts suppresses the current–voltage hysteresis and stabilizes the operational device stability at the maximum power point. This is attributed to the suppression of hole trapping at the n‐type selective transport layer (SnO2)/perovskite interface observed by surface photovoltage spectroscopy, which is interpreted to reduce interfacial recombination and improve charge carrier extraction. The best and most stable performance of 19% is achieved using potassium nitrate as the interface modifier. Devices with higher and more stable performance exhibit substantially lower current transients, analyzed during maximum power point tracking.

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The impact of sodium on the electrical properties of Cu(In,Ga)Se2 (CIGS) thin films and corresponding solar cells was investigated by preparing nearly alkali-free CIGS layers and doping them with different Na amounts via NaF post-deposition treatment (PDT) at temperatures between 110 and 400 °C. The mean Na concentrations in the CIGS layers ranged from 0.1 to 400 ppm. Sodium was found also in the grain interior even for the lowest PDT temperature. All samples were subjected to extensive electrical characterization: current–voltage, capacitance profiling, conductivity, steady-state, and transient capacitance spectroscopy. A continuous increase in open-circuit voltage VOC and fill factor FF, an accompanying increase in hole density and mobility, and a decrease in secondary barriers responsible for the distortion of current–voltage characteristics were observed with increasing sodium content. An abrupt change in defect spectra and a dominant transport mechanism was found for PDT temperatures T(PDT) of ≥150 °C. We attribute a further improvement in VOC observed above 150 °C PDT temperature to the reduced concentration of recombination centers with increased sodium content. An explanation of both gradual evolution and the abrupt change is proposed based on passivation of grain boundaries and interfaces by sodium.

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