@article{darabi_chauhan_guo_wang_seyitliyev_bateni_wang_ghasemi_taussig_woodward_et al._2024, title={Cationic ligation guides quantum-well formation in layered hybrid perovskites}, volume={7}, ISSN={["2590-2385"]}, DOI={10.1016/j.matt.2024.09.010}, number={12}, journal={Matter}, publisher={Accepted}, author={Darabi, K. and Chauhan, M. and Guo, B. and Wang, J. and Seyitliyev, D. and Bateni, F. and Wang, T. and Ghasemi, M. and Taussig, L. and Woodward, N. and et al.}, year={2024}, month={Dec}, pages={4410–4425} }
 @article{thapa_chauhan_cranston_guo_lessard_dougherty_amassian_2024, title={Linking Electronic and Structural Disorder Parameters to Carrier Transport in a Modern Conjugated Polymer}, volume={8}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.4c10298}, DOI={10.1021/acsami.4c10298}, abstractNote={Understanding charge transport in conjugated polymers is crucial for the development of next-generation organic electronic applications. It is presumed that structural disorder in conjugated polymers originating from their semicrystallinity, processing, or polymorphism leads to a complex energetic landscape that influences charge carrier transport properties. However, the link between polymer order parameters and energetic landscape is not well established experimentally. In this work, we successfully link statistical surveys of the local polymer electronic structure with paracrystalline structural disorder, a measure of statistical fluctuations away from the ideal polymer packing structure. We use scanning tunneling microscopy/spectroscopy to measure spatial variability in electronic band edges in PM6 films, a high-performance conjugated polymer, and find that films with higher paracrystallinity exhibit greater electronic disorder, as expected. In addition, we show that macroscopic charge carrier mobility in field effect transistors and and trap influence in hole-only diode devices is positively correlated with these microscopic structural and electronic parameters.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Thapa, Gaurab J. and Chauhan, Mihirsinh and Cranston, Rosemary R. and Guo, Boyu and Lessard, Benoit H. and Dougherty, Daniel B. and Amassian, Aram}, year={2024}, month={Aug} }
 @article{gwalani_martin_kautz_guo_lambeets_olszta_battu_malakar_yang_guo_et al._2024, title={Mechanistic understanding of speciated oxide growth in high entropy alloys}, volume={15}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-024-49243-8}, abstractNote={Complex multi-element alloys are gaining prominence for structural applications, supplementing steels, and superalloys. Understanding the impact of each element on alloy surfaces due to oxidation is vital in maintaining material integrity. This study investigates oxidation mechanisms in these alloys using a model five-element equiatomic CoCrFeNiMn alloy, in a controlled oxygen environment. The oxidation-induced surface changes correlate with each element's interactive tendencies with the environment, guided by thermodynamics. Initial oxidation stages follow atomic size and redox potential, with the latter becoming dominant over time, causing composition inversion. The study employs in-situ atom probe tomography, transmission electron microscopy, and X-ray absorption near-edge structure techniques to elucidate the oxidation process and surface oxide structure evolution. Our findings deconvolute the mechanism for compositional and structural changes in the oxide film and will pave the way for a predictive design of complex alloys with improved resistance to oxidation under extreme conditions.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Gwalani, Bharat and Martin, Andrew and Kautz, Elizabeth and Guo, Boyu and Lambeets, S. V. and Olszta, Matthew and Battu, Anil Krishna and Malakar, Aniruddha and Yang, Feipeng and Guo, Jinghua and et al.}, year={2024}, month={Jun} }
 @article{mcandrews_guo_kaczaral_fukuda_poma_belisle_amassian_mcgehee_2024, title={Moisture Uptake Relaxes Stress in Metal Halide Perovskites at the Expense of Stability}, ISSN={["2380-8195"]}, url={https://doi.org/10.1021/acsenergylett.4c01817}, DOI={10.1021/acsenergylett.4c01817}, abstractNote={Previous studies have shown that the degradation rate of metal halide perovskites in an ambient atmosphere increases with the amount of tensile stress, which primarily arises from the coefficient of thermal expansion mismatch with the substrate. In this work, we show the first evidence of tensile stress relaxation in perovskite films resulting from moisture uptake. Indeed, for multiple perovskite compositions we observe that tension relaxes rapidly in ambient conditions, as compared to inert conditions, with quartz crystal microbalance measurements showing a mass density increase on a similar time scale indicative of moisture uptake. The uptake of moisture at free surfaces, including grain boundaries, can reduce tension in a constrained film, similar to how adatom diffusion reduces residual stress following thin film formation. Unfortunately, the uptake of moisture can catalyze other degradation mechanisms such as PbI2 formation or a transition to a nonperovskite structural phase. Stress-induced uptake of moisture is an especially important problem for all-inorganic perovskites because they are annealed at much higher temperatures, causing high tensile stress. It explains the unusually poor ambient stability of these perovskites. Using a diethyl ether antisolvent bath to attach CsPbI2Br to the substrate at a much lower temperature, we reduced the initial tensile strain from 0.43 ± 0.04% to 0.12 ± 0.05%, thus reducing the driving force for moisture uptake and improving its ambient phase stability by over a factor of 15.}, journal={ACS ENERGY LETTERS}, author={McAndrews, Gabriel R. and Guo, Boyu and Kaczaral, Samantha C. and Fukuda, Karen and Poma, Matteo R. S. and Belisle, Rebecca A. and Amassian, Aram and McGehee, Michael D.}, year={2024}, month={Jul} }
 @article{shen_zhang_xu_steele_chen_chen_zheng_li_guo_yang_et al._2024, title={Strain regulation retards natural operation decay of perovskite solar cells}, ISSN={["1476-4687"]}, DOI={10.1038/s41586-024-08161-x}, journal={NATURE}, author={Shen, Yunxiu and Zhang, Tiankai and Xu, Guiying and Steele, Julian A. and Chen, Xiankai and Chen, Weijie and Zheng, Guanhaojie and Li, Jiajia and Guo, Boyu and Yang, Heyi and et al.}, year={2024}, month={Oct} }
 @article{mcandrews_ahmad_guo_kaczaral_amassian_rolston_mcgehee_2024, title={Why Perovskite Thermal Stress is Unaffected by Thin Contact Layers}, ISSN={["1614-6840"]}, url={https://doi.org/10.1002/aenm.202400764}, DOI={10.1002/aenm.202400764}, abstractNote={Abstract Metal halide perovskite photovoltaics have emerged as a high efficiency, low‐cost alternative that can potentially rival or enhance conventional silicon technology. Despite exceptional initial power conversion efficiencies, achieving compliance with international standards and widespread adoption requires further enhancements to their operational stability. Notably, addressing mechanical strain and stress in brittle perovskites has emerged as a pivotal approach to mitigate chemical degradation and improve reliability during thermal cycling. In this study, a popularized strain engineering strategy is investigated in which a high coefficient of thermal expansion (CTE) hole transport layer (i.e., PDCBT) is cast onto inorganic perovskite (CsPbI 2 Br) at 100 °C. Contrary to previously published results, the X‐ray diffraction (XRD):Sin 2 ψ and substrate curvature measurement techniques show that the hole transport layer has no discernible impact on perovskite strain. The accuracy of the XRD:Sin 2 ψ method for measuring strain is highlighted in contrast to an analysis based on shifts of single XRD peaks which can be influenced by multiple artifacts. The findings in this study are in accordance with mechanics theory: thin layers are unable to induce significant strain changes in perovskite thin films as the force they apply is negligible compared to that applied by a thick and stiff substrate.}, journal={ADVANCED ENERGY MATERIALS}, author={McAndrews, Gabriel R. and Ahmad, Muneeza and Guo, Boyu and Kaczaral, Samantha C. and Amassian, Aram and Rolston, Nicholas and McGehee, Michael D.}, year={2024}, month={Jun} }
 @article{guo_chauhan_woodward_mcandrews_thapa_lefler_li_wang_darabi_mcgehee_et al._2023, title={<i>In situ</i> Stress Monitoring Reveals Tension and Wrinkling Evolutions during Halide Perovskite Film Formation}, volume={9}, ISSN={["2380-8195"]}, url={http://dx.doi.org/10.1021/acsenergylett.3c02079}, DOI={10.1021/acsenergylett.3c02079}, abstractNote={Metal halide perovskites (MHPs) are promising candidates for next-generation thin film photovoltaics and high-performance tandems. Solution-processed MHP films are susceptible to residual stress that can induce undesirable surface wrinkles. However, the origins and evolution of stress during solution processing remain elusive. In this work, we utilize multimodal in situ characterizations, including substrate curvature, reflectance, absorbance, and photoluminescence, to monitor stress and morphology evolution during MHP film formation. A film formation model emerges, consisting of a perovskite top crust on a semirigid sol with the ability to transfer mechanical forces. The phase transformation induces tension in the MHP crust, while shrinkage of the sol causes additional compression and surface wrinkles. Wrinkle-free films are formed through dynamically balancing forces between the crust and the sol. This study provides a powerful toolkit for the fast-growing area of stress engineering in MHP photovoltaics to achieve dynamic control of film stress and surface morphology.}, number={1}, journal={ACS ENERGY LETTERS}, author={Guo, Boyu and Chauhan, Mihirsinh and Woodward, Nathaniel R. and McAndrews, Gabriel R. and Thapa, Gaurab J. and Lefler, Benjamin M. and Li, Ruipeng and Wang, Tonghui and Darabi, Kasra and McGehee, Michael D. and et al.}, year={2023}, month={Dec}, pages={75–84} }
 @article{ghasemi_guo_darabi_wang_wang_huang_lefler_taussig_chauhan_baucom_et al._2023, title={A multiscale ion diffusion framework sheds light on the diffusion-stability-hysteresis nexus in metal halide perovskites}, ISSN={["1476-4660"]}, DOI={10.1038/s41563-023-01488-2}, abstractNote={Stability and current-voltage hysteresis stand as major obstacles to the commercialization of metal halide perovskites. Both phenomena have been associated with ion migration, with anecdotal evidence that stable devices yield low hysteresis. However, the underlying mechanisms of the complex stability-hysteresis link remain elusive. Here we present a multiscale diffusion framework that describes vacancy-mediated halide diffusion in polycrystalline metal halide perovskites, differentiating fast grain boundary diffusivity from volume diffusivity that is two to four orders of magnitude slower. Our results reveal an inverse relationship between the activation energies of grain boundary and volume diffusions, such that stable metal halide perovskites exhibiting smaller volume diffusivities are associated with larger grain boundary diffusivities and reduced hysteresis. The elucidation of multiscale halide diffusion in metal halide perovskites reveals complex inner couplings between ion migration in the volume of grains versus grain boundaries, which in turn can predict the stability and hysteresis of metal halide perovskites, providing a clearer path to addressing the outstanding challenges of the field.}, journal={NATURE MATERIALS}, author={Ghasemi, Masoud and Guo, Boyu and Darabi, Kasra and Wang, Tonghui and Wang, Kai and Huang, Chiung-Wei and Lefler, Benjamin M. and Taussig, Laine and Chauhan, Mihirsinh and Baucom, Garrett and et al.}, year={2023}, month={Feb} }
 @article{wang_li_ardekani_serrano-lujan_wang_ramezani_wilmington_chauhan_epps_darabi_et al._2023, title={Sustainable materials acceleration platform reveals stable and efficient wide-bandgap metal halide perovskite alloys}, volume={6}, ISSN={["2590-2385"]}, DOI={10.1016/j.matt.2023.06.040}, abstractNote={The vast chemical space of emerging semiconductors, like metal halide perovskites, and their varied requirements for semiconductor applications have rendered trial-and-error environmentally unsustainable. In this work, we demonstrate RoboMapper, a materials acceleration platform (MAP), that achieves 10-fold research acceleration by formulating and palletizing semiconductors on a chip, thereby allowing high-throughput (HT) measurements to generate quantitative structure-property relationships (QSPRs) considerably more efficiently and sustainably. We leverage the RoboMapper to construct QSPR maps for the mixed ion FA1−yCsyPb(I1−xBrx)3 halide perovskite in terms of structure, bandgap, and photostability with respect to its composition. We identify wide-bandgap alloys suitable for perovskite-Si hybrid tandem solar cells exhibiting a pure cubic perovskite phase with favorable defect chemistry while achieving superior stability at the target bandgap of ∼1.7 eV. RoboMapper’s palletization strategy reduces environmental impacts of data generation in materials research by more than an order of magnitude, paving the way for sustainable data-driven materials research.}, number={9}, journal={MATTER}, author={Wang, Tonghui and Li, Ruipeng and Ardekani, Hossein and Serrano-Lujan, Lucia and Wang, Jiantao and Ramezani, Mahdi and Wilmington, Ryan and Chauhan, Mihirsinh and Epps, Robert W. and Darabi, Kasra and et al.}, year={2023}, month={Sep}, pages={2963–2986} }
 @article{zhang_darabi_nia_krishna_ahlawat_guo_almalki_su_ren_bolnykh_et al._2022, title={A universal co-solvent dilution strategy enables facile and cost-effective fabrication of perovskite photovoltaics}, volume={13}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-021-27740-4}, DOI={10.1038/s41467-021-27740-4}, abstractNote={Cost management and toxic waste generation are two key issues that must be addressed before the commercialization of perovskite optoelectronic devices. We report a groundbreaking strategy for eco-friendly and cost-effective fabrication of highly efficient perovskite solar cells. This strategy involves the usage of a high volatility co-solvent, which dilutes perovskite precursors to a lower concentration (<0.5 M) while retaining similar film quality and device performance as a high concentration (>1.4 M) solution. More than 70% of toxic waste and material cost can be reduced. Mechanistic insights reveal ultra-rapid evaporation of the co-solvent together with beneficial alteration of the precursor colloidal chemistry upon dilution with co-solvent, which in-situ studies and theoretical simulations confirm. The co-solvent tuned precursor colloidal properties also contribute to the enhancement of the stability of precursor solution, which extends its processing window thus minimizing the waste. This strategy is universally successful across different perovskite compositions, and scales from small devices to large-scale modules using industrial spin-coating, potentially easing the lab-to-fab translation of perovskite technologies.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Zhang, Hong and Darabi, Kasra and Nia, Narges Yaghoobi and Krishna, Anurag and Ahlawat, Paramvir and Guo, Boyu and Almalki, Masaud Hassan S. and Su, Tzu-Sen and Ren, Dan and Bolnykh, Viacheslav and et al.}, year={2022}, month={Jan} }