**3.2 Applications in regular or inverted structure perovskite solar cells**

The 2D-perovskites have many applications; it is used in solar cells, light emitting diodes, etc. Here we will concentrate on their applications in the n-i-p normal structure and p-i-n inverted structure solar cells as follows: In 2015, Cao and co-workers fabricated a 2D-perovskite thin-film and recorded an efficiency of 4.02% with a regular structure n-i-p with a device structure FTO/TiO2/2D perovskite/spiro-OMeTAD/Au [65]. In 2016, Hsinhan Tsai and co-workers reported a photovoltaic efficiency of 12.52% with no hysteresis for an inverted structure solar cell FTO/PEDOT:PSS/(BA)2(MA)3Pb4I13/PCBM/Al [66]. In 2018, Xinqian Zhang and co-workers fabricated a vertically orientated highly crystalline 2D (PEA)2(MA)n–1PbnI3n + 1, n = 3, 4, 5) films with the assistance of an ammonium thiocyanate (NH4SCN) additive. Planar-structured PSC with the device structure of ITO/PEDOT:PSS/(PEA)2(MA)4Pb5I16 (*n* = 5)/PC61BM/BCP/Ag was fabricated. They got an efficiency up to 11.01% with the optimized NH4SCN addition at *n* = 5 [67]. In the same year, Chunqing Ma and co-workers fabricated a 2D-PSC with the device configuration ITO/PEDOT:PSS/PDAMA3Pb4I13/C60/BCP/Ag and recorded an efficiency of 13% with PDAMA3Pb4I13 (PDM: propane-1,3-diammonium) as the 2D-perovskite layer using p-i-n inverted structure [67].
