| In recent years,halide perovskite solar cells have attracted widespread attention due to their excellent photoelectric properties,simple preparation process,and low cost.Currently,although the organic-inorganic hybrid perovskite has achieved a photoelectric conversion efficiency of 25.5%,it has the problem of being easily decomposed in a hot/humid environment.In contrast,the all-inorganic CsPbI3 perovskite has excellent thermal stability.However,due to the relatively small radius of the cesium ion in the structure,the lead-iodine octahedral structure cannot be effectively supported,which leads to the problem of phase instability at room temperature.In addition,the high-performance cubic phase CsPI3 perovskite material and the TiO2 electron transport layer required in the high-efficiency devices need the higher preparation temperatures,which greatly increases the difficulty of device preparation.In response to the above problems,this thesis systematically studies the growth mechanism and key factors affecting its photoelectric performance by designing the structure of all-inorganic perovskite materials,which aims to realize the low-temperature preparation of high-efficiency and stable all-inorganic perovskite devices.The research contents are summarized as follows:(1)Use calcium ion(Ca2+)to partially replace Pb2+.The radius of Ca2+is 100 pm,which is smaller than the radius of Pb2+(119 pm).Using Ca2+instead of Pb2+can increase the tolerance factor of the perovskite,and then improve the stability of the orthogonal phase CsPbI3(y-CsPbI3)perovskite.The ?-CsPbI3 film can be prepared by the solution method at a low temperature of 60? which is significantly lower than the formation temperature of cubic phase CsPbI3(?-CsPbI3)(>320?).The introduction of Ca2+ reduces the cohesive energy of the crystal structure and increases the tolerance factor from 0.807 to 0.8083.The addition of Ca2+effectively slows down the crystallization rate of the crystal,which improves the morphology and crystal quality of the film,thereby improving the transmission efficiency of carriers in the perovskite film.?-CsPb1-xCaxI3 perovskite device achieves a photoelectric conversion efficiency(PCE)of 9.20%,and the device has no obvious hysteresis.The stability of the device gradually improves with the increase of Ca2+ doping concentration.After 130 h of thermal aging at 80?,the device doped with 2%Ca2+,can still maintain 86%of the initial efficiency.(2)The dimethyl sulfoxide complex of lead iodide(PbI2-(DMSO)2)has been used as the lead source to partially replace lead iodide(PbI2),and the CsPbI3-xBrx perovskite film is prepared by a one-step solution method.The results show that PbI2-(DMSO)2 presents a faster dissolution rate than that of PbI2,and a large number of perovskite colloidal nuclei are formed and grow up at the same time,thereby obtaining a solution with a narrower size distribution of CsPbI3 colloidal particles.The research results show that a solution with uniform CsPbI3 colloidal size distribution is conducive to the formation of high-preferred orientation,low defect density and dense perovskite film,thereby effectively improving the performance and stability of the devices.The photoelectric conversion efficiency of 14.15%can be achieved from the devices prepared with PbI2:PbI2-(DMSO)2=1:4 solution.The unencapsulated device using PbI2-(DMSO)2 as the lead source can maintain 76.54%of the initial PCE after 480 h in an air environment(RH:20%-30%,T:20?).(3)Cesium pivalate(CsTa)with a large steric hindrance radius is introduced into the CsPbI3-xBrX(x<1)perovskite film.The addition of CsTa make the perovskite crystal structure change from slightly distorted ? phase to ? phase,which reduces the overall cohesive energy of the perovskite;the steric hindrance effect of the tert-butyl group can effectively block the tilt of the lead-iodine octahedron,which reduces the possibility of nucleation of non-perovskite phase on the crystal surface;the strong[Pb-Ta]bond replaces the[Pb-1]bond on the crystal surface,which increases the energy barrier of vacancy defect generation on the crystal surface,thereby inhibiting the nucleation of the non-perovskite phase caused by the disorder of the crystal lattice;the decomposition temperature of CsTa is 424?,which can effectively maintain the perovskite structure during the long-term heat treatment;the introduction of CsTa can control the growth kinetics of crystals,which is helpful for the formation of films with high preferred orientation,high crystallinity,low defect concentration,high carrier lifetime and low surface Gibbs free energy.The CsPbI3-xBrx device added with CsTa can achieve a photoelectric conversion efficiency of 14.70%and excellent environmental stability.The CsTa-added perovskite devices can maintain 80%of its initial PCE after being aged for 1900 h in an air environment(RH:?20%).The CsPbI3-xBrx devices added with CsTa can maintain 87.41%of the initial efficiency after 500 h under the environment of RH=80%and T=80?.In addition,the devices prepared by the HPbI3 lead source can achieve a maximum photoelectric conversion efficiency of 16.59%,and it can still maintain 80%of the initial efficiency after more than 1,000 hours in the air.(4)Research on low-temperature electron transport layer for the preparation of flexible all-inorganic perovskite devices.A large planar ?-? conjugated tetracarboxyl substituted perylene(PTCA)organic electron transport layer has been synthesized at a low temperature of 65?.First,the PTCA electron transport layer is used in organic-inorganic methylamine lead iodine(MAPbI3)perovskite devices.The results show that PTCA has a suitable energy level matching with perovskite and FTO,which ensures the effective transmission of electrons.In addition,the carboxyl group in PTCA can effectively connect the electron transport layer,perovskite layer and FTO conductive layer,thereby reducing the carrier recombination caused by the interface barrier.A photoelectric conversion efficiency of 16.09%can be achieved from the device with the hard substrate.PTCA-based devices have excellent environmental stability,and can maintain 80.7%of the initial efficiency after 30 days in an environment with a relative humidity of 40%to 50%.A flexible perovskite device based on PTCA is also prepared.The contact between each functional layer of MAPbI3/PTCA/FTO is closer,and the mechanical stability of the flexible device has been enhanced.It can maintain 70-80%of its initial PCE after 50 bending times.For the application of PTCA to the all-inorganic perovskite solar cell,the rigid and flexible cells only obtained photoelectric conversion efficiencies of 4.89%and 2.35%,respectively.The preliminary analysis of the reason for the lower conversion efficiency of the devices may be the preparation temperature is still relatively high for the perovskite layer,which reduces the conductivity of the flexible substrate.Therefore,it is still necessary to further strengthen the research on the method of low-temperature synthesis of high-quality all-inorganic perovskite.However,the results show that the traditional electron transport layer replaced by the PTCA electron transport layer still has a certain potential development. |
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