Low-temperature Synthesized Nickel Oxide Thin Film For Inverted Planar Perovskite Solar Cells

In recent years,organic-inorganic halide perovskite solar cells（PSCs）have made great progress with the power conversion efficiency increasing rapidly from 3.9%in 2009to 22.7%in 2017.At present,there are two major different device configurations:mesoporous structure and planar structure.Among planar structures,the inverted planar PSCs have attracted much attention due to the ease of removing hysteresis and higher stability.For inverted PSCs,it is very important to choose a suitable hole transport material with controlled film quality for improving the device’s efficiency and stability.PEDOT:PSS is one of the most widely used hole transport materials in inverted PSCs.However,its acidic and hydrophilic nature leads to a poor stability of the corresponding device.Hence,many inorganic hole transport materials have been developed to replace PEDOT:PSS in inverted PSCs,such as NiO_x,CuGaO₂,CuCrO₂.Among these materials,NiO_x as a simple binary oxide featuring good chemical stability and various methods for preparation,has attracted considerable interest.However,in many reports,spin-coating and high annealing temperature were required for the film preparation,which limited the application range.Meanwhile,the conductivity of NiO_x is questionable which leads to lower short-circuit photocurrent density and fill factor of the device.To solve the problems mentioned above,the research work of this thesis are as follows:First,NiO_x thin films were prepared by combustion method which was a general strategy for low-temperature preparation of metal oxides thin films.Compared to the NiO_x thin film prepared by conventional sol-gel method,the NiO_x thin film prepared by combustion method shows a better crystallinity and a higher optical transparency.We fabricated perovskite layer by one-step method on different NiO_x thin films.The results indicate that the as-deposited NiO_x film is beneficial for crystal growth of perovskite and charge transport at the NiO_x/perovskite interface.Thus,it led to improvement of the device efficiency from 13.14%to 16.50%.Second,based on the precursor employed in the combustion method,we introduced a low-temperature spray pyrolysis to prepare NiO_x thin film.Meanwhile,the conductivity of the NiO_x film has been improved by doping different amount of Cu.The results reflect that the devices based on spray pyrolysis deposited NiO_x thin films show high uniformity and good reproducibility in performance.At the optimal Cu doping content of 3 at%,the device efficiency has been improved from 16.23%for the undoped sample to 17.69%,with the short-circuit photocurrent density increasing from 19.95 mA/cm² to 21.16mA/cm² and open-circuit photovoltage increasing from 1.02 V to 1.06 V.Moreover,the doping induced better hole extraction at the NiO_x/perovskite interface is also helpful for the device to achieve better long-term stability.