Research On The Preparation Technology And Application Of Inorganic Perovskite Materials For Use In Solar Cells

Compared with organic-inorganic hybrid perovskite,inorganic perovskite has better thermal stability and component stability,which is considered to be one of the most attractive research hotspots in the field of perovskite photovoltaic in recent years.CsPbI,a direct band gap semiconductor material with a suitable band gap(1.73 eV),has become a typical representative of inorganic perovskite because of its high quantum yield,low defect density and long carrier lifetime.However,CsPbI3 material also faces a serious problem:the cubic phase is easy to turn into yellow and wide band-gap δ phase in the ambient atmosphere.Compared with other organic ions,Cs ions are smaller and cannot support stable octahedral structure and form a stable perovskite structure.Therefore,the phase transition of CsPbI3 is the key to the study of inorganic perovskite.We have mainly done the following work:(1)It is demonstrated that employing a small quantity of triple cation NH3+C2H4NH2+C2H4NH3+(denoted as DETA3+)could effectively stabilize mutableα-CsPbI3 for 60 d via a facile one-step deposition method without any encapsulation.Reasons for the remarkable improvement of phase-stability for CsPbI3 are generalized into three aspects:1)the reduction of CsPbI3 crystalline grains,2)avoiding spontaneous octahedra tilting caused by ion bonds between NH3+ or RNH2+ groups of DETA3+ and I-of[PbI6]4-in CsPbI3 perovskite crystal formed on the surface or grain boundaries of the CsPbI3 and 3)enhancement of hydrophobicity of inorganic perovskite layers induced by the oil-wet(hydrophobic)hydrocarbon chains of DETA3+ aggregated on the surfaces..Excellent photovoltaic properties of the CsPbl3·xDETAI3 perovskite films with reduced nonradiative recombination are achieved.The best solar cell with the configuration of FTO/compact-TiO2/CsPbl3·xDETAI3/P3HT/Au shows a power conversion efficiency(PCE)of 7.89%and retains 92%of initial PCE after storage for 1008 h stored in a dark dry box without any encapsulation.(2)P-phenylenediammonium iodide(PPDI)was employed to post-treat on CsPbI3 films for controlling the phase conversion,strengthening moisture resistance and improving device performance.The multiple roles of PPDI were as follows:1)Avoiding spontaneous octahedral tilting by ionic bonds between NH3+ of PPD2+ and I-of[PbI6]4-;2)Enhancing the hydrophobicity induced by exactly exposed oil-wet(hydrophobic)benzene rings;3)Passivating surface defects and filling I vacancies.As a result,after the post-treatment,mutable a-CsPbI3 could maintain its a phase for at least 30 d in dry air(<20%RH).The perovskite solar cells(PSCs)with PPDI treatment exhibited reproductive photovoltaic performance with a champion power conversion efficiency(PCE)of 10.4%and 91%of the initial PCE was retained after stored for 504 h in a dark dry box without any encapsulation.(3)Colloidal lead sulfide quantum dots(PbS QDs)synthesized by a hot-injection method were employed as both hole-transporting material(HTM)and water-repelling barrier for all-inorganic α-CsPbI3 perovskite solar cells(PSCs).The CsPbI3 films capped with PbS QDs as HTM demonstrate much improved phase-stability and can remain the black α-phase for at least 30 d without any encapsulation in air.The PSCs with PbS QDs as HTM showed high performance with a power conversion efficiency(PCE)of 7.07%.Furthermore,89%of the original PCE is remained after storage for 504 h without any encapsulation due to strong moisture resistance resulting from hydrophobic ligands of PbS QDs.(4)We fabricated fully-inorganic carbon-based perovskite CsPbBr3 solar cells via sequential deposition method with a PCE of 2.53%and long-time stability over 21 days under ambient air conditions without any encapsulation.An evolution process from tetragonal CsPb2Br5 to CsPb2Br5-CsPbBr3 composites to quasi-cubic CsPbBr3 was found.Our results are helpful to the development of inorganic perovskite solar cells and the CsPb2Br5 based optoelectronic devices.In summary,we have effectively stabilized CsPbI3 in black phase at room temperature through DETAI3 additive method and PPDI post-treatment method,and made reasonable explanations.In addition to the phase stability of CsPbI3 layer,the expensive organic hole transport materials containing water absorbing components also accelerate this phase transition process.Therefore,we have studied the application of lead sulfide quantum dots,an inorganic hole transport material,in CsPbI3 perovskite solar cells.In addition,CsPbBr3 solar cells with carbon electrode were prepared by continuous deposition method and CsPb2Br5 was found as the intermediate phase.