Investigations On The Synthesis And Optoelectronic Applications Of Novel Perovskite Materials

Photovoltaic technology which could directly convert clean solar energy into electrical energy has drawn extensive attentions in the environment and energy research.In a long history,the most popular photovoltaics are based on Si solar cells.However,the Si solar cells are faced with issues such as high production costs,complicated and energy consumption processes and large environmental pollution in the production process.As an alternative technique,the third generation solar cells aim for low cost and high efficiency have been heavily investigated.Among them,the organic-inorganic hybrid perovskite solar cells with higher photo-electric conversion efficiency and lower cost have been one of the most promsing candidates for the furture PV techque.As for the development of high peroformance perovskite solar cell,the quality of perovskite film plays a critical role.In this dissertation,we developed a series of effective strategies for the preparation of high-quality,high-stability perovskite films.The main highlights and conclusions of this dissertation are summarized as follows:1.By using a novel volume-expansion-adjustable PbI₂·xMAI?x:0.1–0.3?precursor film to replace pure PbI₂,the facile morphology-controllable sequential deposition of planar CH₃NH₃PbI₃?MAPbI₃?film was realized.The use of additive MAI during the first step of deposition leads to the reduced crystallinity of PbI₂ and the pre-expansion of PbI₂ into PbI₂·xMAI with adjustable morphology,which result in about 10-fold faster formation of planar MAPbI₃ film?without PbI₂ residue?and thus minimize the negative impact of the solvent isopropanol on perovskites during the MAI intercalation/conversion step.A best efficiency of 17.22%is obtained for a planar perovskite solar cell based on PbI₂·0.15MAI.2.A facile non-CH₃NH₃I one step fabrication of high quality MAPbI₃perovskite via direct gas/solid deposition of spin coating HI+PbI₂ precursor solution in low concentration CH₃NH₂ atmosphere was successfully developed.This HI+PbI₂ precursor solution was prepared by direct addition of stoichiometric aqueous HI acid into PbI₂ DMF solution without any other chemical synthesis process.This novel one step approach can be extended to fabricate different lead halide perovskites such as MAPbI₂Br and C₂H₅NH₂PbI₃ by spin coating HBr+PbI₂ precursor solution in CH₃NH₂atmospheres or HI+PbI₂ in C₂H₅NH₂ atmospheres,respectively.Our novel one-step approach is a promising candidate for fabricating high performance perovskite by one step reaction of gaseous CH₃NH₂ with HX and PbX₂?X=I,Br?.3.Furthermore,the controllable formation of grain boundary PbI₂nanoplates passivated MAPbI₃ and MAPbI₂Br perovskites for high performance solar cells was realized by the modified gas/solid deposition method.The PbI₂ passivated planar perovskite films were facilely prepared via direct gas/solid reaction of hydrohalide deficient PbI₂·xHI/Br precursor with CH₃NH₂ gas.The amount of PbI₂ impurities can be controlled by adjusting the hydrohalide deficiency in the precursors.The PbI₂ with controllable amount locating at grain boundary could effectively passivate the perovskites with a longer PL lifetime.Both MAPbI₃ and MAPbI₂Br perovskite solar cells via MA+?PbI₂·0.95HI/Br?exhibit improved PV performance with the enhanced V_oc due to less charge recombination by PbI₂ passivation.In contrast,the MA+?PbI₂·0.90HI/Br?samples fabricated solar cells exhibited lower efficiency with worse fill factor or lower J_sc due to the perovskites'reduced crystalline or the hindered electron transfer by too much PbI₂ crystals.4.High stable and high performance all inorganic CsPbI₃ perovskite solar cell was fabricated by combining the precusor engineering with dimension control.By using PbI₂·xHI and CsI as precursors,the?-?phase transformation temperature of CsPbI₃ could be reduced from 350°C to¹00°C;Furthermore,adding a small amount of 2D EDAPbI₄ perovskite containing ethylene diamine?EDA?cation into the precusor could effectively stabilize the?-CsPbI₃ to avoid the undesirable formation of the non-perovskite delta phase.Moreover,the 2D perovskite of EDAPbI₄ not only help?-CsPbI₃ perovskite films show high phase stability at room temperature for months and at 100°C for>150 h,but also corresponding?-CsPbI₃ perovskite solar cells?PSCs?exhibit highly reproducible efficiency of 11.8%,a record for all-inorganic lead halide PSCs.The enhanced phase stability could be ascribed to both the reduced crystal size via formation of 2D/3D perovskite of CsPbI₃·xEDAPbI₄ and the nature of?110?layered EDAPbI₄.5.Crosslinked 2D/3D NH₃C₄H₉COO-?MA?_n Pb_nBr_3n perovskite planar films with controllable quantum confine was desgined and fabricated by the addition of bi-functional 5-Aminovaleric acid?Ava?into regular MAPbBr₃ perovskite precursor solutions.Both the NH₃⁺and the COO^-groups of the zwitterionic amino acid is proposed to crosslink the atomic layer MAPbBr₃ units via Pb-COO bond and ion bond between NH₃⁺and[PbX₆]unit.The Raman characterizations confirmed a successful fabrication Ava?MAPbBr₃?n 2D/3D structure instead of a mixture of cation-alloy Ava_xMA1-xPbBr₃.The quantum confine effect and fluorescence performance of this bifunctional crosslinked 2D/3D Ava?MAPbBr₃?n perovskite films could be facilely tuned by simply change the molar ratio between the Ava and MA.The smooth and stable Ava?MAPbBr₃?₂ film shown an PLQY of⁸0%.