Novel Inorganic Hole Transporting Materials:Design,Preparation And Application In Perovskite Solar Cells

Organic-inorganic hybrid Perovskite solar cells（PSCs）are favored by researchers due to their potential for high power conversion efficiency（PCE）and low manufacturing cost.Since it was first reported in 2009,after more than ten years of rapid development,the maximum efficiency of laboratory single-junction devices has reached 25.7%,surpassing CdTe,CuInGaSe and other cells,and comparable to traditional silicon-based solar cells.Its rapid development is expected to promote a new round of photovoltaic technology revolution.However,poor stability limits the pace of commercialization,which is mainly reflected in the widely used organic hole transport material（HTM）containing additives,such as Spiro-MeOTAD,P3HT,PTAA,etc.At the same time,the synthesis process of organic HTM is complex and costly.In contrast,inorganic HTM has low cost and high stability.However,the photoelectric properties of traditional inorganic HTM are not ideal,so it is not suitable to be used as high-performance hole transport layer（HTL）directly.Therefore,it is very important to develop novel high-performance inorganic HTM,construct interface friendly and matching energy level of HTL for the development of highly stable perovkite solar cells.In this case,focusing on the key problems of perovskite solar cells toward device stability,this paper proposed the employment of novel inorganic hole transport materials,the design of new device structures,the development of interface regulation of new ideas,so as to achieve high efficiency and stability of perovskite solar cells.The main research progress is as follows:Firstly,CuCrO₂ nanocrystals are a kind of inorganic HTM with great potential.However,their intrinsic conductivity is low and interface carrier recombination is serious.Therefore,in this work,Mg²⁺is introduced into the lattice by doping low-valence metal ion to improve its intrinsic conductivity.Subsequently,CuCrO₂ hole transport layer with porous structure is constructed.On the one hand,the interface contact area between HTM and perovskite is increased,and the distance of hole transporting is shortened.On the other hand,the gradient energy level is formed to enhance the carrier transport performance.Finally,the device achieves a PCE of 21.64%with excellent photo-thermal stability.It lays an important research foundation for the performance regulation of efficient hole transport materials.Secondly,in order to develop novel inorganic hole transport materials with higher efficiency,CuScO₂ nanocrystals were prepared at low temperature by solution method for the first time,and used as HTL of PSCs.In view of the advantages of the porous hole transport structure,the mesoscopic structure is further designed to achieve effective hole transport and enhanced light capture.Subsequently,an ion compensation strategy was proposed to passivate the interface between HTL and perovskite by pre-treating HTL with formamidine salt（FAI）,which effectively repaired the ion loss defect at the interface of buried perovskite film.In collaboration with perovskite top passivation technology,the methylamine-free inverted PSCs obtained a PCE of 22.42%with excellent device stability.Moreover,when the absorbing layer is replaced by triple-cation perovskite,the PCE of the device reach to 23.11%.Thirdly,in view of the surface defects between perovskite and HTL,it is proposed to introduce inorganic p-type quantum dots（PbS）into the superficial layer（forming a type of interface gradient heterojunction）.The strong Pb-S interaction can inhibit the formation of surface defects and improve the performance of hole extraction.At the same time,the surface ligands of quantum dots have obvious hydrophobic properties,which can significantly improve the environmental stability of the devices.Based on this gradient heterojunction,the formal device obtained a PCE of 21.07%and excellent long-term environmental stability.This research demonstrates the multipurpose of inorganic quantum dot materials.Finally,while improving the interface contact between perovskite and inorganic HTL,the mismatch of energy levels at the perovskite/electron transport layer interface is also one of the key factors to limit the performance of PSCs.Therefore,this work proposes to introduce a layer of inorganic nanocrystalline material（TiO₂）with low valence band at the interface to form a double-layer cascade(TiO₂/PC₆₁BM/ZnO).On the one hand,a gradient conduction band energy level can be formed,which is conducive to the efficient transport of electrons.On the other hand,a low valence band can inhibit the reverse transport of holes.Therefore,both CsPbI₂Br and Cs/FA-based wide-band gap（E_g=1.73eV）inverted perovskite solar cells have obtained excellent photoelectric conversion efficiency（15.10%and 18.12%）and improved device stability.