High-efficient solid-state perovskite solar cell without lithium salt in the hole transport material

CH3NH3PbX (X = Br, I, Cl) perovskites have recently been used as light absorbers in hybrid organic-inorganic solid-state solar cells, with efficiencies above 15%. To date, it is essential to add Lithium bis(Trifluoromethanesulfonyl)Imide (LiTFSI) to the hole transport materials (HTM) to get a higher conductivity. However, the detrimental effect of high LiTFSI concentration on the charge transport, DOS in the conduction band of the TiO2 substrate and device stability results in an overall compromise for a satisfactory device. Using a higher mobility hole conductor to avoid lithium salt is an interesting alternative. Herein, we successfully made an efficient perovskite solar cell by applying a hole conductor PTAA (Poly[bis(4-phenyl) (2,4,6-trimethylphenyl)-amine]) in the absence of LiTFSI. Under AM 1.5 illumination of 100 mW/cm2, an efficiency of 10.9% was achieved, which is comparable to the efficiency of 12.3% with the addition of 1.3 mM LiTFSI. An unsealed device without Li+ shows interestingly a promising stability. © 2014 World Scientific Publishing Company.