Alkali Salts as Interface Modifiers in n‐i‐p Hybrid Perovskite Solar Cells

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.

Potassium iodide reduces the stability of triple-cation perovskite solar cells

“…13,14 In order to address these issues, various passivation strategies have been explored, such as the introduction of polymers or larger cations into the perovskite layer that can improve both luminescence quantum yields and moisture stability. [15][16][17][18][19][20][21] However, the presence of such macromolecules oen impedes charge transport if not managed properly and controlling mixed phase lms using larger cations can also compromise device efficiency. To directly passivate defects in a perovskite, interest has turned to the use of inorganic additives.…”

The use of nickel oxide as a hole transport material in perovskite solar cell configuration: Achieving a high performance and stable device

“…87 Introducing potassium-based alkali salts at the ETL/perovskite interface helps to improve carrier extraction, stability and suppress trapping of charges at the interface. 88 Understanding crystal growth, physics of defects and instability of perovskites would be a step forward to improving features of PSCs. 89 A planar SnO 2 /TiO 2 double layer oxide can be incorporated to enhance charge extraction, reduce carrier recombination and increase device stability.…”

Post‐Treatment of Mesoporous Scaffolds for Enhanced Photovoltage of Triple‐Mesoscopic Perovskite Solar Cells

“…Particularly, alkali salts have been proved effective for enhancing the electronic properties of the ETL and passivating the grain boundary of the perovskites. [ 33–37 ] Graetzel and co‐workers treated the mesoporous TiO 2 with lithium bis(trifluoromethanesulfonyl)imide, and achieved PSCs with an efficiency of over 19% and negligible hysteresis. [ 37 ] Park and co‐workers doped mixed‐cation perovskites with various alkali iodide, and effectively reduced the hysteresis effect of PSCs.…”