Highly ordered crystallization of α-FAPbl_(3) films via homogeneous seeds for efficient perovskite solar cells

Formamidine lead triiodide(FAPbI_(3))perovskites have become the most promising photovoltaic materials for perovskite solar cells with record power conversion efficiency(PCE).However,random nucleation,phase transition,and lattice defects are still the key challenges limiting the quality of FAPbI_(3) films.Previous studies show that the introduction or adding of seeds in the precursor is effective to promote the nucleation and crystallization of perovskite films.Nevertheless,the seed-assisted approach focuses on heterogeneous seeds or hetero-composites,which inevitably induce a lattice-mismatch,the genera-tion of strain or defects,and the phase segregation in the perovskite films.Herein,we first demonstrate that high-quality perovskite films are controllably prepared using α-and δ-phases mixed FAPbI_(3) micro-crystal as the homogeneous seeds with the one-step antisolvent method.The partially dissolved seeds with suitable sizes improve the crystallinity of the perovskite flm with preferable orientation,improved carrier lifetime,and increased carrier mobility.More importantly,the α-phase-containing seeds promote the formation of α-phase FAPbI_(3) films,leading to the reduction of residual lattice strain and the suppres-sion of I-ion migration.Besides,the adding of dimethyl 2,6-pyridine dicarboxylate(DPD)into the pre-cursor further suppresses the generation of defects,contributing to the PCE of devices prepared in air ambient being significantly improved to 23.75%,among the highest PCEs for fully air-processed FAPbI_(3) solar cells.The unpackaged target devices possess a high stability,maintaining 80%of the initial PCE under simulated solar illumination exceeding 800 h.

离子液体界面修饰的高效稳定FAPbI_(3)钙钛矿太阳能电池

碘铅甲眯(FAPbI_(3))钙钛矿太阳能电池因其优异的光伏性能而受到广泛关注,但器件的长期稳定性仍然是FAPbI_(3)太阳能电池的关键问题。FAPbI_(3)黑色钙钛矿相在室温下会相变为黄色非钙钛矿相,且水分会加速这一相变。界面工程是提高钙钛矿太阳能电池稳定性的常用方法之一。作为绿色溶剂,离子液体被认为是有毒界面修饰剂的潜在替代品,这也提高了它们的商业可行性,并加速了它们在可再生能源市场的应用。本研究利用具有低挥发性、低毒性、高导电性和高热稳定性的离子液体1-乙基-3-甲基咪唑四氟硼酸盐(EMIM[BF_(4)])来修饰钙钛矿太阳能电池的电子传输层和钙钛矿层之间的界面。离子液体的引入不仅减少了界面缺陷,而且提高了钙钛矿薄膜的质量。密度泛函理论计算表明,离子液体与钙钛矿表面之间存在较强的界面相互作用,有利于降低钙钛矿表面缺陷态密度,稳定钙钛矿晶格。除钙钛矿薄膜缺陷外,溶液处理的SnO_(2)也存在表面缺陷。在SnO_(2)表面的缺陷产生缺陷态,也会导致能带对准问题和稳定性问题。密度泛函理论计算表明,有离子液体的表面间隙态比没有离子液体的表面间隙态小,这种减弱的表面间隙态表明表面区域载流子复合减少,有利于提高器件性能。因此,我们实现了功率转换效率大于22%的离子液体修饰的FAPbI_(3)钙钛矿太阳能电池(对照21%)。在相对湿度~20%的干箱中存放1800h以上后,冠军器件保留了初始状态的~90%,而控制器件降解为非钙钛矿黄色六方相(δ-FAPbI_(3))。

Advances to Stabilize Photoactive Phase of FAPbI_(3)Perovskite

Recently,hybrid organic-inorganic perovskite materials have drawn widespread attention because of their outstanding optoelectrical properties(i.e.,high absorption coefficient,long carrier diffusion distance),hence they are suitable light-absorbing materials for photovoltaic application.Among all perovskite materials,formamidinium lead iodide(FAPbI3)based solar cells exhibit impressive power conversion efficiency(PCE)at laboratory stage,showing great potential to compete with silicon-based solar cell.However,FAPbI3 still suffers from poor phase stability which is the prior problem that needs to be addressed before its further commercialization.To be precise,the photoactive phase(αphase)is thermodynamically metastable at room temperature,which not only makesαphase tend to transform into photoinactive phase(δphase),but also causes competitive crystallization between two phases during the film preparation process,making it hard to fabricate pureα-FAPbI3 films.In our review,we summarized key factors that are vital for obtaining high-quality FAPbI3 perovskite thin films and enhancing the stability of FAPbI3 photoactive phase.First of all,precursor solution stability is of great importance since the conditions of precursor solution determine the nucleation and crystal growth process of perovskite.By introducing coordinating additives,using FAPbI3 single crystal as raw material or applying co-solution strategy,the impurities formed by side reaction during precursor solution aging can be effectively suppressed,thus the stability of FAPbI3 solution can be greatly prolonged.Second,the crystallization kinetics of FAPbI3 have been systematically manipulated to obtain dense and large grain size perovskite films.Through introducing intermediate phase,regulating the surface energy,and retarding the crystal growth of FAPbI3 in crystallization process,not only films without pinholes and fewer grain boundaries can be obtained,the pre-formedδphase at room temperature can also be well-suppressed,thus high-qualityα-FAPbI3 films can be obtained.Third,how to thermodynamically enhance the phase stability of acquired FAPbI3 film has been extensively studied.The Gibbs free energy of FAPbI3 photoactive phase can be reduced through composition engineering,dimension engineering and external additives engineering,hence the phase transition barrier fromαphase toδphase has been significantly improved,which further enhance the phase stability ofα-FAPbI3.Lastly,we pointed out challenges of each method and proposed potential applications of mentioned strategies on improving the stability of all kinds of perovskite materials,thus further boost the commercialization of perovskite solar cell devices.

Ligand exchange engineering of FAPbI_(3) perovskite quantum dots for solar cells

Formamidinium lead triiodide(FAPbI_(3))perovskite quantum dots(PQDs)show great advantages in photovoltaic applications due to their ideal bandgap energy,high stability and solution processability.The anti-solvent used for the post-treatment of FAPbI_(3) PQD solid flms signifcantly afects the surface chemistry of the PQDs,and thus the vacancies caused by surface ligand removal inhibit the optoelectronic properties and stability of PQDs.Here,we study the efects of diferent anti-solvents with diferent polarities on FAPbI_(3) PQDs and select a series of organic molecules for surface passivation of PQDs.The results show that methyl acetate could efectively remove surface ligands from the PQD surface without destroying its crystal structure during the post-treatment.The benzamidine hydrochloride(PhFACl)applied as short ligands of PQDs during the post-treatment could fll the A-site and X-site vacancies of PQDs and thus improve the electronic coupling of PQDs.Finally,the PhFACl-based PQD solar cell(PQDSC)achieves a power conversion efciency of 6.4%,compared to that of 4.63%for the conventional PQDSC.This work provides a reference for insights into the surface passivation of PQDs and the improvement in device performance of PQDSCs.

Hyperbranched phthalocyanine enabling black-phase formamidinium perovskite solar cells processing and operating in humidity open air

The extreme instability of pureα-phase FAPbI_(3) under high humidity conditions restricts the highthroughput fabrication in unmodified air environments,resulting in poor performance ofα-phase FAPbI_(3) perovskite devices obtained by scalable fabrication methods.Here we synthesized hyperbranched copper phthalocyanine(HCuPc)as a supramolecular additive with twisted phthalocyanine units to realize the molecular-level encapsulation at the grain boundaries through supramolecular interaction,which greatly broadened the processing window of FAPbI_(3) under high humidity.At the same time,unlike traditional encapsulation layer that carrier can only be collected by tunneling effect,the twisted phthalocyanine ring of HCu Pc in perovskite films is more conducive to hole extraction.Finally,a record efficiency was achieved in pure FAPbI_(3) based inverted structured solar cell by blade-coating to the best of our knowledge,even under unmodified humid air conditions(relative humidity of 65%–85%).The best operational stability of 3D pure FAPbI_(3) devices can also be achieved at the same time and unencapsulated HCuPc-FAPbI_(3) device can even operate with negligible degradation for 100 h in the open air(RH 30%–40%).