Room-Temperature And Solution-Processable Cu-Doped Nickel Oxide Nanoparticles For Efficient Perovskite Solar Cells

Organic-inorganic hybrid perovskite have been rapidly developed owing to the excellent properties of ambipolar transport behavior,high extinction coefficient,simple fabrication processes and low cost.Perovskite solar cells?PSCs?have become the research hotspot in photovoltaic field and the power conversion efficiency?PCE?has reached 22.7%.Among the different device structures of PSCs,the inverted planar PSCs have been paid more and more attentions because of their simple structure and fabrication process.As an important part of the device structure,the material selection of hole-transport layer?HTL?directly affects the performance of PSCs.Nickel oxide?NiO_x?is the most commonly used inorganic hole transport material due to its advantages:such as good energy level matching with perovskite,high stability and low cost.However,compared to the organic hole transport materials,the conductivity of NiO_x is not good enough,which will affect the efficiency of PSCs.metal ion doping is an effective approach to improve the conductivity of NiO_x.In this paper,we reported Cu:NiO_x NPs-based films with good electrical properties as efficient HTLs for high-performance flexible inverted planar MAPbI₃ PSCs.Such Cu:NiO_x NPs-based HTLs could be readily fabricated on various substrates?rigid indium tin oxide?ITO?/glass and flexible ITO/polyethylene naphthalate?PEN??with large-area uniformity by the room-temperature solution process of high-quality Cu:NiO_x NPs prepared by a facile chemical co-precipitation method.The main research contents are as follows:Firstly,Cu:NiO_x NPs were prepared using the chemical co-precipitation method.The results showed that Cu:NiO_x NPs had good dispersion in aqueous solution and the NPs aqueous solutions had good stability and could be stored in the ambient environment over several months without obvious precipitation.The X-ray diffraction?XRD?analysis and TEM images exhibited that the doping of Cu element increased the lattice spacing of Ni O and decreased the size of NPs.Furthermore,the Cu:NiO_x films are fabricated by the room-temperature solution process.The results showed that the Cu:NiO_x films consisted of smaller-sized crystalline grains and were uniform over large area compared with the pristine NiO_x film.In addition,Cu-doping could effectively improve the conductivity of the thin film.Compared with the hole mobility of 3.05×10^-3 cm²/?V·S?for the pristine NiO_x film,the hole mobility of the Cu:NiO_x film reached 1.05×10^-2 cm²/?V·S?when the Cu doping concentration was2%.Furthermore,the Cu:NiO_x films were used as the hole transport layers for the inverted planar PSCs.The results showed that the perovskite films grown on Cu:NiO_x films are denser and the grain size and the absorption intensity increases.Compared to the pritstine NiO_x film,the capability of hole extraction and transmission of Cu:NiO_x films was improved.Originating from the improved electrical performance of Cu:NiO_x NPs,the photovoltaic performance of PSCs on the rigid ITO glass was significantly improved from 15.47%for the pristine NiO_x NPs HTL to 18.66%for the Cu:NiO_x NPs HTLs and the hysteresis effect was significantly inhibited.In the stability experiment,the stability of Cu:NiO_x-based cell was enhanced in the same environment.Finally,a flexible large-area perovskite solar cell with high efficiency was fabricated.Similarly,Cu:NiO_x HTL also showed better performance compared to the NiO_x HTL in flexible PSCs.When the active area of the flexible PSCs was 0.10 cm²,the maximum PCE of Cu:NiO_x-based device reached 17.16%,and the PCE of NiO_x-based device was only 14.27%.When the active area was 1.08 cm²,the efficiency of the flexible cell increased from 12.29%for the Cu:NiO_x-based cell to15.42%for the Cu:NiO_x-based cell.