Single-crystal halide perovskites: Opportunities and challenges

Single-crystal halide perovskites have received growing attention due to their high carrier-transport efficiency and excellent stability in comparison with their polycrystalline counterparts. This review is timely, since it gives a comprehensive overview of the advances in single-crystal halide perovskite, including their unique physical properties, controllable crystal growth, and, most importantly, device applications. In the end, we share our perspectives on the remaining challenges and potential solutions for driving this emerging field forward. This review will provide food for thought to researchers in the field and a jump-start to beginners who want to join this exciting field. Single-crystal halide perovskites have demonstrated excellent optoelectronic properties and promising device application potentials, thanks to their remarkable carrier dynamics, solution processing procedures, and outstanding stabilities. The latest progress and future perspectives of single-crystal halide perovskites are reviewed herein. The basic properties and fundamental studies of single-crystal halide perovskites are first discussed. We then introduce the growth methods for these materials and summarize their recent developments. We further present the single-crystal halide perovskite devices among their major application fields. Finally, we discuss current challenges and provide some suggestions for their further development. We hope this paper can help readers understand the status and future challenges for single-crystal halide perovskites. Single-crystal halide perovskites have demonstrated excellent optoelectronic properties and promising device application potentials, thanks to their remarkable carrier dynamics, solution processing procedures, and outstanding stabilities. The latest progress and future perspectives of single-crystal halide perovskites are reviewed herein. The basic properties and fundamental studies of single-crystal halide perovskites are first discussed. We then introduce the growth methods for these materials and summarize their recent developments. We further present the single-crystal halide perovskite devices among their major application fields. Finally, we discuss current challenges and provide some suggestions for their further development. We hope this paper can help readers understand the status and future challenges for single-crystal halide perovskites. As a class of emerging semiconductors, halide perovskites hold significant potentials for multiple fields. However, current halide perovskite electronic devices are heavily focused on polycrystalline thin films, primarily due to the simplicity of depositing polycrystals.1Chen Y. He M. Peng J. Sun Y. Liang Z. Structure and growth control of organic-inorganic halide perovskites for optoelectronics: from polycrystalline films to single crystals.Adv. Sci. 2016; 3: 1500392Crossref Scopus (139) Google Scholar,2Park N.G. Zhu K. Scalable fabrication and coating methods for perovskite solar cells and solar modules.Nat. Rev. Mater. 2020; 5: 333-350Crossref Scopus (125) Google Scholar Despite their successful use cases in various devices, polycrystalline halide perovskite thin films face many challenges that greatly impede their further research, development, and commercialization of those devices. A high density of structural defects is typically present in the polycrystalline thin films, including point defects (e.g., vacancies, interstitials, and substitutional antisites), impurities, dislocations, grain boundaries, and residual precipitates (e.g., PbI2 cluster and metallic Pb from the fast antisolvent deposition process).3Ball J.M. Petrozza A. Defects in perovskite-halides and their effects in solar cells.Nat. Energy. 2016; 1: 16149Crossref Scopus (395) Google Scholar Those defects result in non-radiative carrier loss,4Shi D. Adinolfi V. Comin R. Yuan M. Alarousu E. Buin A. Chen Y. Shi D. Hoogland S. Rothenberger A. et al.Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals.Science. 2015; 347: 519-522Crossref PubMed Scopus (2787) Google Scholar material degradation,5Chen L. Tan Y.-Y. Chen Z.-X. Wang T. Hu S. Nan Z.-A. Xie L.-Q. Hui Y. Huang J.-X. Zhan C. et al.Toward long-term stability: single-crystal alloys of cesium-containing mixed cation and mixed halide perovskite.J. Am. Chem. Soc. 2019; 141: 1665-1671Crossref PubMed Scopus (20) Google Scholar device hysteresis,6Kong W. Wang S. Li F. Zhao C. Xing J. Zou Y. Yu Z. Lin C.-H. Shan Y. Lai Y.H. et al.Ultrathin perovskite monocrystals boost the solar cell performance.Adv. Energy Mater. 2020; 10: 2000453Crossref Scopus (5) Google Scholar and many other detrimental effects.7Fu M. Tamarat P. Trebbia J.-B. Bodnarchuk M.I. Kovalenko M.V. Even J. Lounis B. Unraveling exciton–phonon coupling in individual FAPbI3 nanocrystals emitting near-infrared single photons.Nat. Commun. 2018; 9: 3318Crossref PubMed Scopus (54) Google Scholar,8Ni Z. Bao C. Liu Y. Jiang Q. Wu W.-Q. Chen S. Dia X. Chen B. Hartweg B. Yu Z. et al.Resolving spatial and energetic distributions of trap states in metal halide perovskite solar cells.Science. 2020; 367: 1352-1358Crossref PubMed Scopus (126) Google Scholar Single-crystal halide perovskites, on the contrary, exhibit a largely suppressed density of those structural defects due to the ordered lattice arrangement. This structural superiority bestows the single-crystal halide perovskites with several attractive benefits, which has garnered growing attention in the field.8Ni Z. Bao C. Liu Y. Jiang Q. Wu W.-Q. Chen S. Dia X. Chen B. Hartweg B. Yu Z. et al.Resolving spatial and energetic distributions of trap states in metal halide perovskite solar cells.Science. 2020; 367: 1352-1358Crossref PubMed Scopus (126) Google Scholar, 9Kelso M.V. Mahenderkar N.K. Chen Q. Tubbesing J.Z. Switzer J.A. Spin coating epitaxial films.Science. 2019; 364: 166PubMed Google Scholar, 10Shi E. Yuan B. Shiring S.B. Gao Y. Akriti C S. D X. C B. H B. Y Z. et al.Two-dimensional halide perovskite lateral epitaxial heterostructures.Nature. 2020; 580: 614-620Crossref PubMed Scopus (52) Google Scholar, 11Lei Y. Chen Y. Zhang R. Li Y. Yan Q. Lee S. Yu Y. Tsai H. Choi W. Wang K. et al.A fabrication process for flexible single-crystal perovskite devices.Nature. 2020; 583: 790-795Crossref PubMed Scopus (43) Google Scholar, 12Chen Y. Lei Y. Li Y. Yu Y. Cai J. Chui M.-H. Rao R. Gu Y. Wang C. Choi W. et al.Strain engineering and epitaxial stabilization of halide perovskites.Nature. 2020; 577: 209-215Crossref PubMed Scopus (100) Google Scholar In this review, we summarize the advances that have been made to date in developing single-crystal halide perovskites, with a focus on their property merits, growth methods, and use cases. Finally, we share our thoughts on several outstanding challenges, inviting more researchers to contribute to this exciting field. Compared with conventional semiconductors, halide perovskites show structural as well as compositional versatility, which confers fascinating semiconductive properties for a wide range of applications. Perovskite was first discovered by German mineralogist Gustav Rose in Russian's Ural Mountains in 1839.13Rose G. Description of some new minerals from the Urals.Ann. Phys. 1839; 124: 551-573Crossref Scopus (20) Google Scholar Perovskites share the same ABX3 crystal structure. In halide perovskites, A is a general cation that can be organic or inorganic, B is a metallic cation, and X is a halide anion.14Boyd C.C. Cheacharoen R. Leijtens T. McGehee M.D. Understanding degradation mechanisms and improving stability of perovskite photovoltaics.Chem. Rev. 2019; 119: 3418-3451Crossref PubMed Scopus (399) Google Scholar Specifically, common A-site cations include Cs+,15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar Rb+,16Saliba M. Matsui T. Domanski K. Seo J.-Y. Ummadisingu A. Zakeeruddin S.M. Correa-Baena J.-P. Tress W.R. Abate A. Hagfeldt A. Grätzel M. Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance.Science. 2016; 354: 206-209Crossref PubMed Scopus (2278) Google Scholar K+,17Abdi-Jalebi M. Andaji-Garmaroudi Z. Cacovich S. Stavrakas C. Philippe B. Richter J.M. Alsari M. Booker E.P. Hutter E.M. Pearson A.J. et al.Maximizing and stabilizing luminescence from halide perovskites with potassium passivation.Nature. 2018; 555: 497-501Crossref PubMed Scopus (724) Google Scholar methylammonium (MA+),18Xiao K. Lin R. Han Q. Hou Y. Qin Z. Nguyen H.T. Wen J. Wei M. Yeddu V. Saidaminov M.I. et al.All-perovskite tandem solar cells with 24.2% certified efficiency and area over 1 cm2 using surface-anchoring zwitterionic antioxidant.Nat. Energy. 2020; 5: 870-880Crossref Scopus (48) Google Scholar formamidinium (FA+),19Lu H. Liu Y. Ahlawat P. Mishra A. Tress W.R. Eickemeyer F.T. Yang Y. Fu F. Wang Z. Avalos C.E. et al.Vapor-assisted deposition of highly efficient, stable black-phase FAPbI3 perovskite solar cells.Science. 2020; 370: eabb8985Crossref PubMed Scopus (57) Google Scholar dimethylammonium (DMA+),20Ke W. Spanopoulos I. Stoumpos C.C. Kanatzidis M.G. Myths and reality of HPbI3 in halide perovskite solar cells.Nat. Commun. 2018; 9: 4785Crossref PubMed Scopus (116) Google Scholar ethylammonium (EA+),21Chu Z. Zhao Y. Ma F. Zhang C.-X. Deng H. Gao F. Ye Q. Meng J. Yin Z. Zhang X. You J. Large cation ethylammonium incorporated perovskite for efficient and spectra stable blue light-emitting diodes.Nat. Commun. 2020; 11: 4165Crossref PubMed Scopus (32) Google Scholar guanidinium (GUA+),22Jodlowski A.D. Roldán-Carmona C. Grancini G. Salado M. Ralaiarisoa M. Ahmad S. Koch N. Camacho L. de Miguel G. Nazeeruddin M.K. Large guanidinium cation mixed with methylammonium in lead iodide perovskites for 19% efficient solar cells.Nat. Energy. 2017; 2: 972Crossref Scopus (249) Google Scholar tetramethylammonium (TMA+),23Huang C. Lin P. Fu N. Liu C. Xu B. Sun K. Wang D. Zeng X. Ke S. Facile fabrication of highly efficient ETL-free perovskite solar cells with 20% efficiency by defect passivation and interface engineering.Chem. Commun. 2019; 55: 2777-2780Crossref PubMed Google Scholar tetrabutylammonium (TBA+),24Poli I. Eslava S. Cameron P. Tetrabutylammonium cations for moisture-resistant and semitransparent perovskite solar cells.J. Mater. Chem. A. 2017; 5: 22325-22333Crossref Google Scholar and phenylethylammonium (PEA+);25Zhang Y. Liu Y. Xu Z. Ye H. Li Q. Hu M. Yang Z. Liu S.F. Two-dimensional (PEA)2PbBr4 perovskite single crystals for a high performance UV-detector.J. Mater. Chem. C. 2019; 7: 1584-1591Crossref Google Scholar,26Li N. Zhu Z. Chueh C.-C. Liu H. Peng B. Petrone A. Li X. Wang L. Jen A.K.-Y. Mixed cation FAxPEA1–xPbI3 with enhanced phase and ambient stability toward high-performance perovskite solar cells.Adv. Energy Mater. 2017; 7: 1601307Crossref Scopus (217) Google Scholar Common B-site metallic cations include Pb2+,27Kim G. Min H. Lee K.S. Lee D.Y. Yoon S.M. Seok S.I. Impact of strain relaxation on performance of α-formamidinium lead iodide perovskite solar cells.Science. 2020; 370: 108-112Crossref PubMed Scopus (145) Google Scholar Mg2+,28Yang F. Kamarudin M.A. Kapil G. Hirotani D. Zhang P. Ng C.H. Ma T. Hayase S. Magnesium-doped MAPbI3 perovskite layers for enhanced photovoltaic performance in humid air atmosphere.ACS Appl. Mater. Interfaces. 2018; 10: 24543-24548Crossref PubMed Scopus (27) Google Scholar Ca2+,29Chan S.-H. Wu M.-C. Lee K.-M. Chen W.-C. Lin T.-H. Su W.-F. Enhancing perovskite solar cell performance and stability by doping barium in methylammonium lead halide.J. Mater. Chem. A. 2017; 5: 18044-18052Crossref Google Scholar Ba2+,29Chan S.-H. Wu M.-C. Lee K.-M. Chen W.-C. Lin T.-H. Su W.-F. Enhancing perovskite solar cell performance and stability by doping barium in methylammonium lead halide.J. Mater. Chem. A. 2017; 5: 18044-18052Crossref Google Scholar Mn2+,30Liu W. Chu L. Liu N. Ma Y. Hu R. Weng Y. Li H. Zhang J. Li X. Huang W. Efficient perovskite solar cells fabricated by manganese cations incorporated in hybrid perovskites.J. Mater. Chem. C. 2019; 7: 11943-11952Crossref Google Scholar Fe2+,31Boström H.L.B. Bruckmoser J. Goodwin A.L. Ordered B-site vacancies in an ABX3 formate perovskite.J. Am. Chem. Soc. 2019; 141: 17978-17982Crossref PubMed Scopus (11) Google Scholar Ni2+,32Islam M.N. Hadi M.A. Podder J. Influence of Ni doping in a lead-halide and a lead-free halide perovskites for optoelectronic applications.AIP Adv. 2019; 9: 125321Crossref Scopus (18) Google Scholar Cu2+,33Wang K.-L. Wang R. Wang Z.-K. Li M. Zhang Y. Ma H. Liao L.-S. Yang Y. Tailored phase transformation of CsPbI2Br films by copper(II) bromide for high-performance all-inorganic perovskite solar cells.Nano Lett. 2019; 19: 5176-5184Crossref PubMed Scopus (44) Google Scholar Zn2+,34Thapa S. Adhikari G.C. Zhu H. Grigoriev A. Zhu P. Zn-alloyed all-inorganic halide perovskite-based white light-emitting diodes with superior color quality.Sci. Rep. 2019; 9: 18636Crossref PubMed Scopus (18) Google Scholar Cd2+,35Cai T. Yang H. Hills-Kimball K. Song J.-P. Zhu H. Hofman E. Zheng W. Rubenstein B.M. Chen O. Synthesis of all-inorganic Cd-doped CsPbCl3 perovskite nanocrystals with dual-wavelength emission.J. Phys. Chem. Lett. 2018; 9: 7079-7084Crossref PubMed Scopus (43) Google Scholar Ge2+,36Kopacic I. Friesenbichler B. Höfler S.F. Kunert B. Plank H. Rath T. Trimmel G. Enhanced performance of germanium halide perovskite solar cells through compositional engineering.ACS Appl. Energy Mater. 2018; 1: 343-347Crossref Scopus (87) Google Scholar Sn2+,37Lee S.J. Shin S.S. Im J. Ahn T.K. Noh J.H. Jeon N.J. Seok S.I. Seo J. Reducing carrier density in formamidinium tin perovskites and its beneficial effects on stability and efficiency of perovskite solar cells.ACS Energy Lett. 2017; 3: 46-53Crossref Scopus (76) Google Scholar Eu2+,38Xiang W. Wang Z. Kubicki D.J. Tress W. Luo J. Prochowicz D. Akin S. Emsley L. Zhao J. Dietler G. et al.Europium-doped CsPbI2Br for stable and highly efficient inorganic perovskite solar cells.Joule. 2019; 3: 205-214Abstract Full Text Full Text PDF Scopus (204) Google Scholar Tm2+,39Arumugam G.M. Xu C. Karunakaran S.K. Shi Z. Qin F. Zhu C. Chen F. Low threshold lasing from novel thulium-incorporated C(NH2)3PbI3 perovskite thin films in Fabry-Pérot resonator.J. Mater. Chem. C. 2018; 6: 12537-12546Crossref Google Scholar and Yb2+;40Zhou D. Liu D. Pan G. Chen X. Li D. Xu W. Bai X. Song H. Cerium and ytterbium codoped halide perovskite quantum dots: a novel and efficient downconverter for improving the performance of silicon solar cells.Adv. Mater. 2017; 29: 1704149Crossref Scopus (188) Google Scholar Common X-site anions are Cl−,41Liu Y. Yang Z. Cui D. Ren X. Sun J. Liu X. Zhang J. Wei Q. Fan H. Yu F. et al.Two-inch-sized perovskite CH3NH3PbX3 (X= Cl, Br, I) crystals: growth and characterization.Adv. Mater. 2015; 27: 5176-5183Crossref PubMed Scopus (0) Google Scholar Br−,42Fang Y. Wei H. Dong Q. Huang J. Quantification of re-absorption and re-emission processes to determine photon recycling efficiency in perovskite single crystals.Nat. Commun. 2017; 8: 14417Crossref PubMed Scopus (122) Google Scholar I−,43Li X. Zhang F. He H. Berry J.J. Zhu K. Xu T. On-device lead sequestration for perovskite solar cells.Nature. 2020; 578: 555-558Crossref PubMed Scopus (75) Google Scholar formate (HCOO−),44Donlan E.A. Boström H.L.B. Geddes H.S. Reynolds E.M. Goodwin A.L. Compositional nanodomain formation in hybrid formate perovskites.Chem. Commun. 2017; 53: 11233-11236Crossref PubMed Google Scholar and BH4−.45Lang C. Jia Y. Liu J. Wang H. Ouyang L. Zhu M. Yao X. Dehydrogenation and reaction pathway of perovskite-type NH4Ca(BH4)3.Prog. Nat. Sci. Mater. Int. 2018; 28: 194-199Crossref Scopus (3) Google Scholar Depending on the effective radii of the A-site cations, B-site cations, and X-site anions, the crystal lattice of halide perovskites ranges from a highly symmetric cubic structure to a less-symmetric tetragonal or orthorhombic structure (Figure 1A).46Murali B. Kolli H.K. Yin J. Ketavath R. Bakr O.M. Mohammed O.F. Single crystals: the next big wave of perovskite optoelectronics.ACS Mater. Lett. 2020; 2: 184-214Crossref Scopus (20) Google Scholar In general, the backbone of these pseudocubic structures consists of the corner-sharing [BX6] octahedra, with A-site cations occupying the 12-fold coordination sites formed in the middle of eight [BX6] octahedra.47Stranks S.D. Snaith H.J. Metal-halide perovskites for photovoltaic and light-emitting devices.Nat. Nanotechnol. 2015; 10: 391-402Crossref PubMed Scopus (1776) Google Scholar A tolerance factor is usually used to evaluate whether a pseudocubic perovskite structure can be maintained:51Dunlap-Shohl W.A. Zhou Y. Padture N.P. Mitzi D.B. Synthetic approaches for halide perovskite thin films.Chem. Rev. 2019; 119: 3193-3295Crossref PubMed Scopus (197) Google Scholart=rA+rX2(rB+rX),where t is the tolerance factor, rA is the effective radius of the A-site general cation, rB is the effective radius of the B-site metallic cation, and rX is the effective radius of the X-site halide anion. Empirically, a halide perovskite structure with a calculated t ranging from 0.8 to 1 is considered to be stable with cubic symmetry (Figure 1B).15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar,46Murali B. Kolli H.K. Yin J. Ketavath R. Bakr O.M. Mohammed O.F. Single crystals: the next big wave of perovskite optoelectronics.ACS Mater. Lett. 2020; 2: 184-214Crossref Scopus (20) Google Scholar,48Li Z. Yang M. Park J.-S. Wei S.-H. Berry J.J. Zhu K. Stabilizing perovskite structures by tuning tolerance factor: formation of formamidinium and cesium lead iodide solid-state alloys.Chem. Mater. 2015; 28: 284-292Crossref Scopus (918) Google Scholar If the size of A is relatively small (e.g., for MA+ cations with a radius of 217 pm15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar), then t would be small, and a tetragonal or orthorhombic structure will be formed. On the other side, if the size of A is too large (e.g., for TBA+ cations with a radius of 494 pm24Poli I. Eslava S. Cameron P. Tetrabutylammonium cations for moisture-resistant and semitransparent perovskite solar cells.J. Mater. Chem. A. 2017; 5: 22325-22333Crossref Google Scholar), the perovskite will adopt a layered two-dimensional (2D) or a linear one-dimensional (1D) structure such as the Ruddlesden-Popper phase, the Dion-Jacobson phase, and the alternating-cation phase (Figure 1C).52Zheng K. Abdellah M. Zhu Q. Kong Q. Jennings G. Kurtz C.A. Messing M.E. Niu Y. Gosztola D.J. Al-Marri M.J. et al.Direct experimental evidence for photoinduced strong-coupling polarons in organolead halide perovskite nanoparticles.J. Phys. Chem. Lett. 2016; 7: 4535-4539Crossref PubMed Scopus (38) Google Scholar The size of B cations (e.g., Pb2+ with a radius of 119 pm15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar and Sn2+ with a radius of 110 pm15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar) usually will not have a big impact on t since they do not change much compared with the size of A. The size of X anions can effectively affect the crystal structure of halide perovskites. For example, MAPbI3 (I− with a radius of 220 pm15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar) adopts a tetragonal structure under room temperature while MAPbBr3 and MAPbCl3 (Br− with a radius of 196 pm15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar and Cl− with a radius of 181 pm15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar) adopt a cubic structure. Also, F−-based halide perovskites are rarely studied due to the small size of the F− anion (129 pm in radius15Kour R. Arya S. Verma S. Gupta J. Banhoria P. Bharti V. Datt R. Gupta V. Potential substitutes for replacement of lead in perovskite solar cells: a review.Glob. Chall. 2019; 3: 1900050Crossref PubMed Google Scholar), which results in a too-small tolerance factor to hold the crystal lattice.53El-Mellouhi F. Marzouk A. Bentria E.T. Rashkeev S.N. Kais S. Alharbi F.H. Hydrogen bonding and stability of hybrid organic-inorganic perovskites.ChemSusChem. 2016; 9: 2648-2655Crossref PubMed Scopus (0) Google Scholar Because of the high tunability in structures and compositions, the halide perovskites show very versatile functionalities.54Zhang W. Eperon G.E. Snaith H.J. Metal halide perovskites for energy applications.Nat. Energy. 2016; 1: 16048Crossref Scopus (443) Google Scholar Halide perovskites are intriguing semiconductors. It has been reported that the valence band maximum of halide perovskites mainly consists of s orbitals of heavy metal ions (e.g., Pb2+) and p orbitals of halide ions (e.g., I–).55Mehmood U. Al-Ahmed A. Afzaal M. Al-Sulaiman F.A. Daud M. Recent progress and remaining challenges in organometallic halides based perovskite solar cells.Renew. Sustain. Energy Rev. 2017; 78: 1-14Crossref Scopus (30) Google Scholar Therefore, substituting the chemical composition can effectively alter the coupling of the orbitals and, consequently, the electronic band structures of the perovskites, which enables a broad range of applications.56Zou C. Chang C. Sun D. Böhringer K.F. Lin L.Y. Photolithographic patterning of perovskite thin films for multicolor display applications.Nano Lett. 2020; 20: 3710-3717Crossref PubMed Scopus (12) Google Scholar, 57Lu M. Zhang Y. Wang S. Guo J. Yu W.W. Rogach A.L. Metal halide perovskite light-emitting devices: promising technology for next-generation displays.Adv. Funct. Mater. 2019; 29: 1902008Crossref Scopus (112) Google Scholar, 58Sun W. Liu Y. Qu G. Fan Y. Dai W. Wang Y. Song Q. Han J. Xiao S. Lead halide perovskite vortex microlasers.Nat. Commun. 2020; 11: 4862Crossref PubMed Scopus (10) Google Scholar, 59Wang K. Xing G. Song Q. Xiao S. Micro- and nanostructured lead halide perovskites: from materials to integrations and devices.Adv. Mater. 2020; 33: 2000306Crossref Scopus (10) Google Scholar With different compositions, halide perovskites show a tunable direct band gap between 1.2 eV and 3.1 eV (Figures 1D and 1E),60Li J. Han Z. Gu Y. Yu D. Liu J. Hu D. Xu X. Zeng H. Perovskite single crystals: synthesis, optoelectronic properties, and application.Adv. Funct. Mater. 2020; 33: 2008684Google Scholar which covers the entire visible spectrum. Besides, halide perovskites demonstrate tunable exciton (bound electron-hole pairs) binding energies (Eb) based on their compositions and dimensions. For the widely studied MAPbI3, Eb is reported to be ∼10 meV,61Yang Z. Surrente A. Galkowski K. Bruyant N. Maude D.K. Haghighirad A.A. Snaith H.J. Plochocka P. Nicholas R.J. Unraveling the exciton binding energy and the dielectric constant in single-crystal methylammonium lead triiodide perovskite.J. Phys. Chem. Lett. 2017; 8: 1851-1855Crossref PubMed Scopus (88) Google Scholar which is much smaller than the thermal energy at room temperature (∼26 meV), indicating that the excitons can easily overcome the Coulombic interaction by thermal fluctuation and become free charge carriers.62Herz L.M. Charge-carrier dynamics in organic-inorganic metal halide perovskites.Annu. Rev. Phys. Chem. 2016; 67: 65-89Crossref PubMed Scopus (384) Google Scholar The free charge carriers can be readily separated and collected upon excitation, which is suitable for photovoltaic and photodetection applications. On the other side, reducing the dimensions of halide perovskites63Zhang F. Lu H. Tong J. Berry J.J. Beard M.C. Zhu K. Advances in two-dimensional organic-inorganic hybrid perovskites.Energy Environ. Sci. 2020; 13: 1154-1186Crossref Google Scholar and changing the composition by substituting the halide ions with others64Wang K. Wang S. Xiao S. Song Q. Recent advances in perovskite micro- and nanolasers.Adv. Opt. Mater. 2018; 6: 1800278Crossref Scopus (94) Google Scholar can effectively increase the Eb to several hundreds of millielectron volts. A large Eb enables enhanced radiative recombination of the charge carriers, which is advantageous for light-emitting applications. Additionally, halide perovskites have shown superior carrier-transport properties. High mobility (up to several hundreds of cm2·V−1·s−1, due to the relatively low electron/hole effective masses65Herz L.M. Charge-carrier mobilities in metal halide perovskites: fundamental mechanisms and limits.ACS Energy Lett. 2017; 2: 1539-1548Crossref Scopus (429) Google Scholar) and long lifetime (up to several microseconds, due to the relatively benign defect chemistry65Herz L.M. Charge-carrier mobilities in metal halide perovskites: fundamental mechanisms and limits.ACS Energy Lett. 2017; 2: 1539-1548Crossref Scopus (429) Google Scholar,66Kim J. Lee S.-H. Lee J.H. Hong K.-H. The role of intrinsic defects in methylammonium lead iodide perovskite.J. Phys. Chem. Lett. 2014; 5: 1312-1317Crossref PubMed Scopus (560) Google Scholar) of charge carriers have been reported in halide perovskites,65Herz L.M. Charge-carrier mobilities in metal halide perovskites: fundamental mechanisms and limits.ACS Energy Lett. 2017; 2: 1539-1548Crossref Scopus (429) Google Scholar contributing to the long charge carrier diffusion length (up to tens of micrometers).47Stranks S.D. Snaith H.J. Metal-halide perovskites for photovoltaic and light-emitting devices.Nat. Nanotechnol. 2015; 10: 391-402Crossref PubMed Scopus (1776) Google Scholar It is worth mentioning that the carrier mobility of halide perovskites is found to be comparable with those of typical inorganic semiconductors (e.g., GaAs).67Brenner T.M. Egger D.A. Rappe A.M. Kronik L. Hodes G. Cahen D. Are mobilities in hybrid organic-inorganic halide perovskites actually “high”?.J. Phys. Chem. Lett. 2015; 6: 4754-4757Crossref PubMed Scopus (143) Google Scholar Fröhlich interaction, which is the intrinsic coupling between carriers and phonons in polar semiconductors,68Dubey S. Paliwal A. Ghosh S. Frohlich interaction in compound semiconductors: a comparative study.Adv. Mater. Res. 2016; 1141: 44-50Crossref Google Scholar relaxes the carriers' initial kinetic energy to the lattice and therefore limits the further increase of carrier mobility in halide perovskites.63Zhang F. Lu H. Tong J. Berry J.J. Beard M.C. Zhu K. Advances in two-dimensional organic-inorganic hybrid perovskites.Energy Environ. Sci. 2020; 13: 1154-1186Crossref Google Scholar Nevertheless, these outstanding carrier-transport properties render halide perovskites extremely suitable for applications like highly efficient photovoltaic, low-limit photodetection, and many others. Meanwhile, halide perovskites typically show a high absorption coefficient up to 105 cm−1 over the entire visible spectrum,69Ahmadi M. Wu T. Hu B. A review on organic-inorganic halide perovskite photodetectors: device engineering and fundamental physics.Adv. Mater. 2017; 41https://doi.org/10.1002/adma.201605242Crossref Scopus (278) Google Scholar due to the strong interband transition.70Wehrenfennig C. Liu M. Snaith H.J. Johnston M.B. Herz L.M. Homogeneous emission line broadening in the organo lead halide perovskite CH3NH3PbI3–xClx.J. Phys. Chem. Lett. 2014; 5: 1300-1306Crossref PubMed Scopus (278) Google Scholar,71De Wolf S. Holovsky J. Moon S.-J. Löper P. Niesen B. Ledinsky M. Haug F.-J. Yum J.-H. Ballif C. Organometallic halide perovskites: sharp optical absorption edge and its relation to photovoltaic performance.J. Phys. Chem. Lett. 2014; 5: 1035-1039Crossref PubMed Scopus (1450) Google Scholar This absorption coefficient is more than one order of magnitude higher than that of Si.72Huang J. Yuan Y. Shao Y. Yan Y. Understanding the physical properties of hybrid perovskites for photovoltaic applications.Nat. Rev. Mater. 2017; 2: 17042Crossref Scopus (527) Google Scholar The high absorption coefficient enables a required absorber thickness of <400 nm in photovoltaic devices, which is much thinner than those made of Si.73Yang Z. Deng Y. Zhang X. Wang S. Chen H. Yang S. Khurgin J. Fang N.X. Zhang X. Ma R. High-performance single-crystalline perovskite thin-film photodetector.Adv. Mater. 2018; 30: 1704333Crossref Scopus (123) Google Scholar Consequently, a reduced device thickness can not only reduce devices' cost significantly, but also potentially suppress the charge carrier recombination and, according to the Shockley-Queisser model,74Krogstrup P. Jørgensen H.I. Heiss M. Demichel O. Holm J.V. Aagesen M. Nygard J. Fontcuberta i Morral A. Single-nanowire solar cells beyond the Shockley-Queisser limit.Nat. Photon. 2013; 7: 306-310Crossref Scopus (569) Google Scholar lead to a high open-circuit voltage (VOC) in photovoltaics. Last but not least, halide perovskites can be processed by low-temperatu