Janardan, D.; Hirselandt, K.; Merdasa, A.; Czudek, A.; Munir, R.; Zu, F.; Koch, N.; Dittrich, Th.; Unger, E.: Alkali salts at Interface modifiers in n-i-p hybrid perovskite solar cells. Solar RRL 3 (2019), p. 1900088/1-10
10.1002/solr.201900088

Abstract:
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.