Interfacial engineering enables high efficiency with a high open-circuit voltage above 1.23V in 2D perovskite solar cells

The hole transport layer (HTL) and electron transport layer (ETL) play critical roles in perovskite solar cells (PVSCs). However, few studies have been done to optimize these two charge transport layers for two-dimensional (2D) PVSCs. Here in this work, both the HTL and ETL of PVSCs based on 2D perovskite (CH3(CH2)(2)NH3)(2)(CH3NH3)(2)Pb3I10 (BA(2)MA(2)Pb(3)I(10)) are optimized to achieve high open-circuit voltage (V-oc) and power conversion efficiency (PCE). The solution-processed NiOx was employed as the HTL to fabricate efficient 2D PVSCs with the structure of indium tin oxide (ITO)/HTL/BA(2)MA(2)Pb(3)I(10)/ETL/bathocuproine (BCP)/Ag. The PCE of the device with [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) as the ETL is increased from 7.99% to 11.01% when NiOx was applied as the HTL instead of the commonly used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The improved performance was attributed to the better matched energy levels and the reduced trap state for NiOx based devices. Considering the deeper HOMO (the highest occupied molecular orbital) level of ICBA (indene-C-60 bisadduct), ICBA was mixed with PCBM as the ETL to reduce the interfacial charge recombination between the perovskite and ETL. This strategy further boosted the PCE to 12.07% with the highest V-oc of 1.23 V for 2D PVSCs so far. This work suggests the potential of interfacial engineering for the performance improvement of 2D PVSCs.