Research On PIN Perovskite Solar Cells Based On Nickel Oxide Hole Transport Layer

In recent years,the power conversion efficiency?PCE?of organic/inorganic perovskite solar cells?PSCs?has rapidly increased from 3.8%to 23.7%.Most high-performance devices require high-quality electron transport layer and hole transport layer?HTL?,respectively.As a kind of inorganic HTL material,nickel oxide has a series of advantages,such as high carrier mobility,excellent stability,high optical transmittance,matched work function with perovskite energy level and simple preparation method,etc.Nickel oxide HTL is widely used in p-i-n type planar PSCs,but the photoelectric conversion efficiency of nickel oxide based PSCs is still lower than that of PEDOT:PSS based PSCs.The main reasons are that the conductivity of nickel oxide thin films is relatively low,the interfacial contact between nickel oxide and perovskite thin film is poor,and the crystallity and quality of the perovskite thin films grown on nickel oxide substrates are inferior.In this thesis,the nickel oxide-based PSCs were studied.To solve the problem of low open-circuit voltage(V_oc)and short-circuit current density(J_sc),the nickel oxide HTL is optimized by PTAA interfacial modification and Na⁺doping,respectively.The preparation of nickel oxide thin films at low temperature by pre-preparation of nickel oxide nanoparticles is also tentatively performed.The contents of this thesis are as follows:?1?In order to achieve low temperature preparation of nickel oxide films,nickel oxide nanoparticles were prepared beforehand and then dispersed evenly in deionized water.NiO_x nanoparticles were prepared by the reaction of NaOH with Ni?NO₃?₂·6H₂O and calcination of resultant Ni?OH?₂ at 270?.The obtained nanoparticles are about30-40nm in size.It was dispersed in deionized water and spin-coated as a HTL for PSCs.The effect of the thickness of NiO_x layer on the performance of PSCs was studied.The optimal PCE of 10.35%is achieved.The poor performance of the device is due to the large and non-uniform size of nanoparticles,which makes it difficult to prepare a uniform,compact and moderately thick HTL,resulting in a large number of defects in the interface between the perovskite and nickel oxide,which deteriorates the J_sc and V_oc of PSCs.?2?We prepare nickel oxide thin films by a simple solution process which is annealed at 300?,and applied to p-i-n type planar PSCs.In view of poor interfacial properties between nickel oxide and perovskite thin films,we propose a method of modifying the surface of NiO_x thin films with organic layer PTAA.The result shows that the PTAA modified layer with appropriate thickness can effectively adjust the quality of perovskite absorption layer with larger grain size and better crystallinity.The J_sc of solar cells has been improved due to the decrease of defect density states of perovskite.In addition,EIS and TRPL measurements show that PTAA modification can effectively improve the charge transfer efficiency between perovskite and HTL.Based on the optimized conditions,PSCs with PCE of 17.1%and no obvisous hysteresis are obtained.?3?On the basis of the above research,in order to improve the conductivity of nickel oxide films,the acceptor ion Na⁺doping is used.The results show that when the concentration is below 3%,Na⁺ion doping can change the surface chemical properties of nickel oxide films and influence the growth of perovskite films.Specifically,it can increase the grain size of perovskite films,reduce the residual lead iodide,improve the crystallinity and decrease the defect density.In addition,the electricalchemical impedance spectroscopy measurement shows that the hole extraction efficiency of nickel oxide film doped with appropriate Na⁺concentration has been improved.The optimum Na⁺doping ratio is fixed at 3mol%based on experimental optimization.Based on this optimal condition,the J_sc of PSCs based on doped nickel oxide HTL has been significantly improved.Finally,PSCs with PCE of 18.44%are obtained.