Design And Physical Properties Research Of Perovskite Optoelectronic Materials

As a new class of optoelectronic semiconductors,perovskite materials show important application prospects in optoelectronic devices such as solar cells,photodetectors,LEDs,etc.due to their intrinsic properties such as high optical absorption coefficient,high defect tolerance,long carrier lifetime and diffusion length.Different from the tetrahedral-bonded optoelectronic semiconductors such as Si and GaN that have been applied on a large scale,perovskite-type optoelectronic materials,as a new type of non-tetrahedral-bonded semiconductor,show unique material advantages and large control range in terms of high optoelectronic performance and low synthesis cost.However,the current challenges for the commercialization of perovskites mainly focus on the Pb toxicity and poor long-term stability.At the same time,the optoelectronic properties of some perovskite-derived systems also need to be further improved.Therefore,theoretical design and physical properties research in terms of detoxification,stability improvement,and optoelectronic properties regulation is one of the important topics in materials science field.Focusing on the above three scientific issues,this work uses first-principles high-throughput calculation methods to conduct material optimization design and physical property control research on several different perovskite systems,and achieve the following innovative achievements:(1)Considering ten experimentally common alloying elements,through firstprinciples high-throughput calculations,exploring the effects of different elements alloying on the toxicity,stability,and electronic properties of single perovskites.Currently,there is still a lack of systematic comparison and in-depth exploration of the effects of different elements alloying in perovskite systems.We considered ten experimentally common alloying elements and divided them into three types according to the presence or absence of the corresponding perovskite phase.Specifically,type I,Sn,Ge,Ca,Sr;type Ⅱ,Cd,Mg,Mn;type Ⅲ,Ba,Zn,Cu.Through first-principles highthroughput calculations combined with cluster expansion methods,we first demonstrated that all these alloys will exist as disordered solid solutions rather than ordered structures at room temperature.Formation energy calculations show that the introduction of Sn and Ge is beneficial to enhance the thermodynamic stability of the cubic perovskite host,while alloying of other elements has no remarkable effect on the stability.Therefore,the introduction of Sn and Ge can realize low toxicity and stable perovskite alloys.For type-I alloys,the bandgap reduction of Sn alloys is due to the energy mismatch between of Sn-5s/5p and Pb-6s/6p orbitals.Sn,Ge alloys exhibit direct band gap,small carrier effective masses,and uniform band-edge charge distribution over the full concentration range and are potential candidates for photovoltaic applications.For type-II alloys,a cubic to hexagonal phase transition occurs at x=0.125,accompanied by a significant increase in the bandgaps and effective masses.The increase in the bandgaps is attributed to the quantum confinement effects.For type-III alloys,the stability reduces significantly with increasing x content.At the same time,the bandgaps and effective masses of the Ba and Zn alloys also tend to increase.Furthermore,electrons and holes are trapped within local potential wells around the Pb atoms,which benefits enhanced quantum yield and self-trapped excitonbased light-emitting applications.Our work provides a theoretical guidance for using alloying strategies to reduce lead toxicity,enhance the stability and optimize the electronic properties of halide perovskites to meet the needs of optoelectronic applications.(2)Multi-element alloying strategy is proposed to effectively improve the stability of double perovskites by increasing the configuration entropy,while the optoelectronic properties of perovskites can also be controlled in a wide range.Improving the stability of perovskite materials is one of the important topics in perovskite research.Inspired by high-stability high-entropy alloys,we theoretically investigated the effects of B-site multi-element alloying on the thermodynamic stability and optoelectronic properties of halide double perovskites through first-principles highthroughput calculations combined with the ideal solid solution model.First,our extensive calculations imply that the interaction between the B-site ions of halide perovskites is weak and allow the formation of multi-element alloys.Next,the calculations for B-site multi-element perovskite alloys reveal that the configurational entropy of alloying is an important driving force for improving the thermodynamic stability of halide double perovskites at finite temperature.The entropy contribution to Gibbs free energy,which offsets the positive enthalpy contribution by up to 35 meV/f.u.,can significantly enhance the material stability of double-perovskite alloys.Meanwhile,the electronic properties of bandgaps(1.04-2.21 eV)and carrier effective masses(0.34 to greater than 2 m0)of the multielement double-perovskite alloys can be tuned over a wide range.In addition,the parity-forbidden condition of optical transitions in the Cs2AgInCl6 perovskite can be broken because of the lower symmetry of the configurational disorder,leading to enhanced transition intensity.Our work demonstrates a promising strategy by utilizing the alloy entropic effect to further improve the material stability and optoelectronic performance of halide perovskites.(3)Basic physical properties research of In2PtX6 vacancy-ordered perovskites,revealed that they can be used as non-toxic optoelectronic candidate materials.Recent reports of vacancy-ordered perovskites have shown that Pt-containing compounds are a new class of potential optoelectronic materials with excellent properties and nontoxicity.We investigated the stability,electronic properties,and optical properties of In2PtX6(X=Cl,Br,I)by using the PBE and mBJ functional.Based on the phonon and AIMD simulation,In2PtX6 perovskites show dynamical and thermodynamic stability.By changing the halide ion from Cl to Br and then to I,the band gaps and effective masses illustrate a decreasing trend.Electronic property calculations show that these structures have direct/indirect transition nature.Among them,the In2PtI6 perovskite has an ideal bandgap of 1.35 eV and SLME of～25%,indicating that this class of vacancy-ordered perovskites has certain application potential in optoelectronic field.Our work provides theoretical guidance for the application of vacancy-ordered perovskites such as In2PtX6 in photovoltaic fields.(4)High-throughput screening and design of inverse-hybrid perovskites to obtain a series of high-performance novel lead-free photovoltaic candidates.Currently,the application of inverse-hybrid perovskites in optoelectronic field is in the initial stage,and still needs further development and exploration.Based on ionic radius matching principle,we designed and constructed 108 X3FA(X is the monovalent organic cation,A is the divalent metal anion)inverse-hybrid perovskites.We investigated the thermodynamic stability and photovoltaic-related properties by firstprinciples high-throughput calculations.Taking the stability and photovoltaic-related properties as screening conditions,we finally obtained five stable photovoltaic candidates with desirable photovoltaic properties.Among them,DA3FNi and M3FNi achieve the SMLE of more than 30%in very thin film thickness of～0.1μm,which is better than that of typical MAPbI3,indicating the promising prospects in ultra-thin film solar cells.In addition,the obvious intrinsic polarization resulted from the unbalanced off-center displacement of ions in inverse-hybrid perovskites,is believed to improve carrier separation and facilitates carrier transport in photovoltaic devices.The transformation of organic cations from relatively free A-sites(in traditional hybrid perovskites)to X-sites bridged within the octahedron(in inverse-hybrid perovskites),increases the energy barrier for organic decomposition.Therefore,the inverse-hybrid perovskites could overcome the instability problem that confusing the current hybrid perovskites.This provides a new solution for improving the stability of the perovskite system from the perspective of material structure.