Organic Molecular Interface Regulation And Mechanism Study Of All-Inorganic Perovskite I-P Layers

Energy depletion and environmental pollution are two serious challenges facing society.In order to solve these problems and realize the sustainable development of energy,the development of clean,pollution-free and huge reserves of solar energy has become a research hotspot.In recent years,perovskite solar cells（PSC）have developed rapidly in the field of photovoltaic because of their excellent photoelectric characteristics and low production cost.Inorganic cesium lead halide(CsPbI_3-xBr_x)perovskite solar cells have made major breakthroughs in the past few years,with power conversion efficiency of more than 20%and thermal and optical stability of hundreds of hours.However,compared with organic-inorganic hybrid perovskite,the phase instability of inorganic perovskite under wet conditions is still the key problem hindering the commercialization of inorganic PSC.However,as an important part of perovskite solar cells,hole transport materials have an important impact on the performance and stability of the cells.Aiming at the problems of low efficiency and poor wet stability of n-i-p devices,we studied the energy loss mechanism and failure path of inorganic perovskite solar cells with hole transport layer and adjacent interface,and put forward the improvement scheme of interface modification and hole layer replacement.This dissertation is mainly divided into the following parts:Firstly,we review the development of solar cells in the introduction of the first chapter,and then summarize the development,preparation and working principle of perovskite solar cells.Secondly,the perovskite/HTL improvement of CsPbI₂Br is studied and related work is repeated in chapters:（1）In the first work,we originally propose that microstrains between the perovskite lattices/grains play a key role in affecting the phase stability of inorganic perovskite.To this end,we innovatively design theπ-conjugated p-typemolecule bis（2-ethylhexyl）3,3’（（4,8-bis（5-（2-ethylhexyl）-3,4-Difluorothiophen-2-y1）benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl）bis（3,3”-dioctyl）[2,2’:5’,2”-terthiophene]-5”,5-diyl）)（2E,2’E）-bis（2-cyanoacrylate）（BTEC-2F）to covalent with the Pb dangling bonds in CsPbI₂Br perovskite film,which significantly suppress the trap states and release the defect-induced local stress between perovskite grains.The interplay between the microstrains and phase stability of the inorganic perovskite are scrutinized by a series of characterizations including x-ray photoelectron spectroscopy,photoluminescence,x-ray diffraction,scanning electron microscopy,and so forth,based on which,we conclude that weaker local stresses in the perovskite film engender superior phase stability by preventing the perovskite lattice distortion under humidity.By this rational design,PSCs based on CsPbI₂Br perovskite system deliver an outstanding power conversion efficiency（PCE）up to 16.25%.The unencapsulated device also exhibits an exceptional moisture stability by retaining over 80%of the initial PCE after 500 h aging in ambient with RH 25%.（2）In the second work,we proposed a novel strategy to significantly inhibit the non-radiative recombination induced by the defect state of the perovskite surface by treating the surface of CsPbI₂Br with polymer（J71）,which resulted in larger plump grain size and further improved the defect-states level at the interface between perovskite and the hole transport layer.In addition,the superhydrophobic J71 surface passivator can not only passivates the surface to prevent water from invading the inner layer,but also further disperses the internal tensile stress between the lattice,thus increasing the crystal spacing and stabilizing the phase and grain size.Results showed that the optimized device has excellent PCE value of more than 16%,and its stability is more than 800h and 650h in nitrogen and humidity environment（>80%retention of initial efficiencies）,respectively.