Crystallization And Dimension Regulation Of Perovskite Light Absorbing Materials In Perovskite Solar Cells

Metal halide perovskite absorbers have attracted enormous attention due to their prominent photoelectronic properties and solution-pressable preparation.Perovskite solar cells(PSCs)have achieved a certificated power conversion efficiency(PCE)of 25.2%.However,the stability still restricts further industrialization of PSCs.Printable mesoscopic PSCs based on the Ti O₂/Zr O₂/C triple mesoscopic layers have good structural stability.Efficient and stable PSCs can be obtained by improving the crystallization of perovskite light-absorbing materials in the mesoscopic layers.On the other hand,two-dimensional(2D)perovskite materials usually have good material stability.The stability of PSCs can be effectively improved by constructing 2D/3D composite perovskite structure.This thesis will focus on the above two aspects as follows:(1)Based on the unique Ti O₂/Zr O₂/C triple mesoscopic inorganic layers of printable mesoscopic PSCs,we reconstructed the crystals of methylaminium(MA)lead iodide perovskite films by post-treating the PSCs with methylamine gas,yielding a homogeneous nucleation and crystallization of the perovskite in printable PSCs.As a result,a uniform,compact and crystalline perovskite layer was obtained after the methylamine gas post-treatment,yielding high PCE of 15.26%,128.8%higher than that of the PSC before processing.More importantly,this post-treatment process allowed the regeneration of the photodegraded PSCs via the crystal reconstruction and the PCE could recover to 91%of the initial value after 2 cycles of the photodegradation-recovery process.(2)2D perovskite light absorbers are reported moisture tolerant,however,the out-of-plane charge transportation is seriously hindered by the organic spacer layer.Hererin,we systhsised a guanine-based 2D perovskite G₂Pb I₄ and characterized the solvated crystal structure,which is consistent with the stable structure obtained by molecular dynamic simulations.In G₂Pb I₄crystal structure,guanine molecules are adjacent to each other,forming a hydrogen bonding network to facilitate the hole transporting.In addition,a cascade of simultaneous proton transfers between guanine cations were observed during the calculation process,suggesting that guanine cations can feature long-range charge transport properties.To gain deeper insights on the role of guanine in low dimensional systems,we have conducted the electronic structure calcution of G₂Pb I₄ and revealed that guanine has an active role in the charge transport.(3)Formamidinium(FA)lead iodide perovskite materials feature promising photovoltaic performances in conjunction with superior thermal stabilities.However,the conversion of the perovskite?-FAPb I₃ phase to the thermodynamically stable yet photovoltaically inactive?-FAPb I₃ phase compromises the photovoltaic performances of PSCs.Herein,we overcome this challenge by employing the 2D perovskite G₂Pb I₄ in 3D FAPb I₃ perovskites,where guaninium spacer layer can act as a stabilizer of?-FAPb I₃ perovskite phase and built a 2D/3D composite structure G₂FA_n-1Pb_nI_3n+1 w/o distinct enlargement of band gaps.As a result,we obtained a highly crystallized homogeneous perovskite film with reduced trap density in n=20 perovskite films,where the charge transportation between perovskite layer and hole-transporting layer was greatly improved.By optimization,a highest PCE of 16.04%was achieved,90%higher than the control cell.In 2D/3D composite films,2D perovskite G₂Pb I₄ was mainly distributed at the grain boundaries,protecting the perovskite layer from moisture.This strategy can realize the combination of high efficiency and high stability for PSCs.(4)We report a perovskite film dominated by three-dimensional(3D)components rather than 2D components by introducing FASCN based on the typical 2D perovskite PEA₂FA₃Pb₄I₁₃.The dimension transformation ehances the optical absorption of films in visible and near-infrared region and leads to an optimized PCE of 14.13%,which is far beyond the control cell.Notably,a spontaneous phase separation was observed in the 3D dominant films where 2D perovskite formed at the surfaces and grain boundaries,protecting the formamidinium based perovskite layer against moisture intrusion and suppressing the trap-assisted recombination.The unencapsulated cell with FASCN exhibited excellent moisture stability during the shelf lifetime measurement over 70 days in ambient condition.This strategy paves a way to realize both the superior stability and the high PCE for PSCs.