Organometallic halide perovskites have attracted much attention as a promising material for high-efficiency absorber in photovoltaic devices. It is based on organic-inorganic light absorbing semiconducting material with a perovskite polycrystalline structure, CH₃NH₃PbX₃, where X is halogenatoms (Cl, Br, I, or combination of some of them). The poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was usually used as a hole extraction layer in planar type perovskite photovoltaic cells. However, PEDOT:PSS showed several disadvantages such as hygroscopic properties and a highly acidic suspension, which result in poor stability in air.

In this respect, we have investigated the possibility of two-dimensional materials including MoS₂, WS₂, and graphene oxide (GO) as a hole extraction layer in perovskite photovoltaic cells. MoS₂ and WS₂ layers with a polycrystalline structure were synthesized by a chemical deposition method using uniformly spin-coated (NH₄)MoS₄ and (NH₄)WS₄ precursor solutions. GO was made by following Hummer’s method. Raman spectra, transmission electron microscope image, and x-ray diffraction data confirmed the well-synthesis of two-dimensional materials. The device structure is indium tin oxide/PEDOT:PSS or MoS₂ or WS₂ or GO/CH₃NH₃PbI_xCl_3-x/bathocurione/LiF:Al. The PCE values of PEDOT:PSS, GO, MoS₂ and WS₂-based one are measured to be 9.93, 9.62, 9.53 and 8.02 %, respectively. These result indicated that two-dimensional materials could replace the PEDOT:PSS layer for the improvement of device stability.