Construction And Performance Optimization Of Large-area And Flexible Inverted PSCs Based On NiO_x Hole Transport Layer

In the past ten years,organic-inorganic hybrid perovskite solar cells have made considerable progress,and their photoelectric conversion efficiency(PCE)has rapidly increased from 3.8%to 25.5%.Until now,most high-efficiency perovskite solar cells have adopted a normal n-i-p structure,and the speed of their development has made researchers cheer up,which can be described as a huge leap.However,it is worth noting that the highest-efficiency formal structural device is a small-area device prepared by a traditional solution spin coating method,which is not conducive to the preparation of large-area devices.Morever,the formal structural device exhibits severe hysteresis and poor stability.In recent years,inverted perovskite solar cells(IPSCs)have attracted an increasing attention due to their negligible hysteresis.Researches have shown that using organic hole transport layers such as poly 3,4-ethylenedioxythiophene/polystyrene sulfonate(PEDOT:PSS)can obtain almost negligible hysteresis devices.However,due to the hygroscopicity of PEDOT:PSS,the stability of the devices are poor.Therefore,this article focuses on inorganic hole-transport materials.Among huge number of inorganic hole-transport materials,nickel oxide(NiO_x)stands out due to its excellent performance.Compared with formal structural devices,the photoelectric conversion efficiency of inverted devices still has a large gap.Therefore,NiO_x-based inverted perovskite solar cells have greater potential value.This paper will focus on the synthesis and optimization of NiO_x,the regulation of perovskite,and the construction of large-area perovskite modules.The specific content is as follows:(1)There are various preparation methods for NiO_x hole-transport layers,but it is still a huge challenge to prepare a NiO_x hole transport layer with excellent performance.In this article,the sol-gel method,chemical precipitation method and combustion method are used to prepare NiO_x hole transport layers on conductive substrates,and the differences in morphology structure and performance of the three hole-transport layers are compared.The results show that the device prepared based on the chemical precipitation method has a relatively high performance and the highest efficiency is 14.22%.Based on this,systematic studies were conducted on the NiO_x hole-transport layer prepared by the chemical precipitation method as according to TEM,AFM and UV-vis optical properties,and further optimized the MAPb I₃perovskite by using Pb Cl₂.It has been found that the addition of Pb Cl₂ can not only produce impurity phases,such as Pb I₂ and MAPb Cl₃,but the presence of impurity phases can also passivate grain boundaries and provide a template for perovskite growth.Meanwhile,Pb Cl₂ can effectively improve the crystallinity of the perovskite and increase the photoelectric conversion efficiency of the device to 17.04%.(2)Due to the low inherent conductivity of NiO_x,serious recombination occurs at the interface of perovskite/NiO_x,and external ion doping is considered to be the most effective method to improve its conductivity.This article prepared Sm-doped nickel oxide(Sm:NiO_x)nanoparticles by chemical precipitation method,and then spin-coated it on the conductive substrate as a hole-transport layer.DFT theoretical calculations show that Sm³⁺doping can reduce the formation energy of Ni vacancies and increase the content of Ni vacancies,thereby effectively increasing the hole density.Furthermore,XPS analysis shows that doping can increase the ratio of Ni³⁺/Ni²⁺,and higher Ni³⁺may lead to an increase in conductivity.UPS analysis shows that the doping makes the Fermi level of NiO_x close to the top of the valence band,which enhances the P-type characteristics of NiO_x.Therefore,the conductivity in the Sm:NiO_x film is significantly improved,and the work function is also increased,which is beneficial to the extraction of holes and the suppression of charge recombination.From the perspective of stability,the Cs FAMA tri-cation perovskite system was applied in this section,and a relatively high device performance of 19.16%was obtained.(3)As the Sm doped NiO_x has relatively high electrical conductivity and the good film-forming properties of NiO_x,it has the prerequisites for the preparation of large-area perovskites solar cell,and the Sm:NiO_x film prepared by the chemical precipitation method just well avoids the process of high-temperature heat treatment,so it also has the conditions for preparing flexible devices.In addition,the photoelectric properties of Cs FAMA and Cs FA perovskite prepared by the bladeing coating method were also compared.The results showed that the Cs FA perovskite is more suitable for the bladeing coating.Therefore Sm:NiO_x was applied specifically for small-area rigid devices,1 cm² large-area devices,and large-area modules prepared by the blade coating method.Based on this,in the obtained devices,the best efficiency of the small area device(0.09 cm²)reached 20.71%,the highest efficiency of the flexible device(0.09 cm²)reached 17.95%,the efficiency of the 1 cm² large area device reached 18.51%,and the efficiency of large area module(8.85 cm²)reaches 15.27%.These efficiencies represent a higher level in the field of NiO_x-based inverted perovskite solar cells.At the same time,the preparation of large-area modules has further promoted the development process of perovskite commercialization.