Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G69: Fundamental Properties of Metal Halide Perovskites IIIRecordings Available
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Sponsoring Units: DMP Chair: Kushantha Withanage, University of Texas El Paso Room: Hyatt Regency Hotel -Jackson Park A |
Tuesday, March 15, 2022 11:30AM - 11:42AM |
G69.00001: Surface and interfacial heterogeneities in hybrid perovskite solar cells Zeeshan Ahmad, Giulia Galli Hybrid organic-inorganic perovskites are promising candidates for photovoltaic and optoelectronic applications with power conversion efficiencies over 25%. There remain unanswered questions about the fundamental reasons for such high efficiencies and widespread disparities observed in experiments. We elucidate the reasons for the observed heterogeneity in the properties of perovskite solar cells by performing first-principles investigations of surfaces and interfaces in methylammonium lead halides. We find a considerable spread in the value of the Rashba spin splitting [1], band alignments, and defect formation energies depending on the surface facet and termination. Our calculations explain some of the disparities in experimental literature. We also provide design guidelines to maximize the efficiencies of perovskite solar cells through control of surfaces and interfaces during synthesis. |
Tuesday, March 15, 2022 11:42AM - 11:54AM |
G69.00002: Entropic stabilization of perovskite structures Alexei V Tkachenko, Igor A Zaliznyak Starting with a theoretical picture of the Coulomb Floppy Network, previously developed for empty perovskite materials, e.g. ScF3, we demonstrate a prominent role played by the entropic effects in a broader context of the entire perovskite family. In the case of ScF3, those effects are essential for understanding a number of anomalous properties: negative thermal expansion, entropic elasticity, thermal stabilization of high symmetry cubic phase, strong anharmonic and colossal pressure-induced softening. A conceptually similar theoretical approach is applicable to regular perovskites, as well. In particular, we show how intrinsically unstable cubic structure gets stabilized at finite temperature thanks to a combination of thermal fluctuations and steric constraints. The same entropic effect also manifests itself in the strong anharmonic of soft phonon modes. |
Tuesday, March 15, 2022 11:54AM - 12:06PM |
G69.00003: Phonon anharmonicity in lead-halide perovskites: CsPbBr3 Renat Sabirianov, Jaeil Bai, Xiao C Zeng, Yinsheng Guo, Wai-Ning Mei Using ab initio molecular dynamics we demonstrate that a highly anharmonic nature of atomic motions in CsPbBr3 is responsible for its unusual temperature of charge carrier lifetime. As temperature increases, vibrational spectra of perovskite structure demonstrate a noticeable shift in frequency and anharmonic atomic motion is observed. We calculated Gru¨neisen parameter as function of pressure. We analyze the thermal expansion of CsPbBr3, discuss multi-phonon processes, phonon coupling and decay pathways. The results are compared with the available experimental Raman spectroscopy. |
Tuesday, March 15, 2022 12:06PM - 12:18PM |
G69.00004: Can Conductivity Goes to Negative Value in Perovskites? Naveen K Tailor, Soumitra Satapathi Recently, halide perovskites have emerged as a promising material for device applications. Lead-based perovskites have been widely explored while investigation of optical properties of lead-free perovskites remains limited. Lead-halide perovskite single crystals have shown light-induced positive photoconductivity, and as lead-free perovskites are optically active, they are expected to demonstrate similar properties. However, we report here light-induced negative photoconductivity with slow recovery in lead free Cs3Bi2Cl9 perovskite. The femtosecond transient reflectance (fs-TR) spectroscopy studies further reveal these electronic transport properties were due to the formation of light-activated metastable trap states within the perovskite crystal. The figure of merits of Cs3Bi2Cl9 single-crystal detectors such as responsivity (17 mA/W), detectivity (6.23 × 1011 Jones) and the ratio of current in dark to light (~7160) was calculated. This observation for Cs3Bi2Cl9 single crystals, which were optically active but showed retroactive photocurrent on irradiation, remained unique for such materials. |
Tuesday, March 15, 2022 12:18PM - 12:30PM |
G69.00005: Excited State Charge Carrier Dynamics in TiO2 wrapped Perovskite Cs2AgBiBr6 Nanocrystals SMRUTI PUROHIT, Kanhaiya L Yadav, Soumitra Satapathi The halide double perovskites (DP) have recently emerged as a potential candidate for photocatalysis, LED, and solar cells applications. Here, we report the excited state carrier dynamics of DP Cs2AgBiBr6 nanocrystals (NCs) wrapped with amorphous TiO2 (a-TiO2). A nanocomposite is formed through the antisolvent recrystallization route by incorporating a-TiO2 around Cs2AgBiBr6 NCs. The optical and electrical properties of DP NC and a-TiO2 coated DP NC were characterized by UV vis, PL, FTIR, and cyclic voltammograms study. The femtosecond transient absorption spectroscopy reveals that the fastest component of lifetime enhances from 1.6 ps to 2.2 ps after TiO2 wrapping confirming efficient suppression of defect states in DP NCs. Finally, these heterostructures were successfully used for CO2 reduction. |
Tuesday, March 15, 2022 12:30PM - 12:42PM |
G69.00006: Absence of a polaron signature in angle-resolved photoemission of CsPbBr3 Oliver Rader, Maryam Sajedi, Maxim Krivenkov, Dmitry Marchenko, Jaime Sánchez-Barriga, Andrei Varykhalov, Emile Rienks, Stefan Blügel, Irene Aguilera, Anoop K Chandran The formation of large polarons has been proposed as reason for the high defect tolerance, low mobility, low charge carrier trapping and low nonradiative recombination rates of lead halide perovskites. In polaronic oxides TiO2 and SrTiO3, polarons lead to an enhanced effective mass in angle-resolved photoemission spectroscopy (ARPES). Recently, evidence for large-polaron formation in CsPbBr3 has been reported from a 50% effective mass enhancement in ARPES relative to band structure calculations [1]. We present in-depth band dispersion measurements of CsPbBr3 to determine the R-point in momentum space and GW calculations that lead to a realistic band gap. We obtain almost identical effective masses at the valence band maximum of 0:202+/-0:016 m0 in experiment and 0.18 m0 (cubic) to 0.223 m0 (orthorhombic) in theory. This means that there is no indication for large polaron formation from ARPES data. |
Tuesday, March 15, 2022 12:42PM - 12:54PM |
G69.00007: A-site Cation Influence on the Conduction Band of Lead Bromide Perovskites and its Connection to Slow Hot Carrier Cooling Gabriel J Man Hot carrier solar cells hold promise for exceeding the Shockley-Queisser limit. Slow hot carrier cooling is one of the most intriguing properties of lead halide perovskites and distinguishes this class of materials from competing materials used in solar cells. Here we use the element selectivity of high-resolution X-ray spectroscopy to uncover a previously hidden feature in the conduction band states, the σ-π energy separation, and find that it is strongly influenced by the strength of electronic coupling between the A- cation and halide-lead sublattice. Our finding provides an alternative mechanism to the commonly discussed polaronic screening and hot phonon bottleneck carrier cooling mechanisms. Our work emphasizes the optoelectronic role of the A-cation, provides a comprehensive view of A-cation effects in the electronic and crystal structures, and outlines a broadly applicable spectroscopic approach for assessing the impact of chemical alterations of the A-cation on halide and potentially non-halide perovskite electronic structure. |
Tuesday, March 15, 2022 12:54PM - 1:06PM |
G69.00008: Inspecting the different expressions of anharmonicity in halide perovskites Sebastián Caicedo-Dávila, Xiangzhou Zhu, Christian Gehrmann, David Egger Although optoelectronic devices based on halide perovskites (HaPs) have achieved outstanding performance, comparable to high-quality inorganic semiconductors, various fundamental aspects of these materials remain puzzling. One key difference to conventional semiconductors is that HaPs exhibit strong vibrational anharmonicities already at room temperature, which are known to influence several optoelectronic properties, including carrier transport and optical absorption characteristics. Here, we investigate different factors that potentially influence the vibrational anharmonicity in HaPs, using molecular dynamics based on density-functional theory. This allows for disentangling the role of A-site dynamics and its coupling to the inorganic framework. Our results help understanding the interrelations of lattice anharmonicity and bonding mechanisms in halide perovskites, possibly providing guidelines for material design. |
Tuesday, March 15, 2022 1:06PM - 1:18PM |
G69.00009: The role of lattice degrees of freedom in the ultrafast optical response of lead-halide perovskites (A)PbBr3. Zhanybek Alpichshev, Dusan Lorenc, Ayan Zhumekenov, Osman M Bakr, Artem Volosniev, Mikhail Lemeshko We use ultrafast laser spectroscopy to study hybrid organo-metallic and all-inorganic lead halide perovskites. By analyzing the time resolved response of the material we demonstrate the importance of lattice degrees of freedom for the strong nonlinear response in lead-halide perovskites. |
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