@article{tang_dang_lee_barrit_munir_wang_li_smilgies_de wolf_kim_et al._2021, title={Wide and Tunable Bandgap MAPbBr
            <sub>
              3−
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            Cl
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            Hybrid Perovskites with Enhanced Phase Stability: In Situ Investigation and Photovoltaic Devices}, volume={5}, ISSN={2367-198X 2367-198X}, url={http://dx.doi.org/10.1002/solr.202000718}, DOI={10.1002/solr.202000718}, abstractNote={The current understanding of the crystallization, morphology evolution, and phase stability of wide‐bandgap hybrid perovskite thin films is very limited, as much of the community's focus is on lower bandgap systems. Herein, the crystallization behavior and film formation of a wide and tunable bandgap MAPbBr3−xClx system are investigated, and its formation and phase stability are contrasted to the classical MAPbI3−xBrx case. A multiprobe in situ characterization approach consisting of synchrotron‐based grazing incidence wide‐angle X‐ray scattering and laboratory‐based time‐resolved UV–Vis absorbance measurements is utilized to show that all wide‐bandgap perovskite compositions of MAPbBr3−xClx studied (0 < x < 3) crystallize the same way: the perovskite phase forms directly from the colloidal sol state and forms a solid film in the cubic structure. This results in significantly improved alloying and phase stability of these compounds compared with MAPbI3−xBrx systems. The phase transformation pathway is direct and excludes solvated phases, in contrast to methylammonium lead iodide (MAPbI3). The films benefit from antisolvent dripping to overcome the formation of discontinuous layers and enable device integration. Pin‐hole‐free MAPbBr3−xClx hybrid perovskite thin films with a tunable bandgap are, thus, integrated into working single‐junction solar cell devices and achieve a tunable open‐circuit voltage as high as 1.6 V.}, number={4}, journal={Solar RRL}, publisher={Wiley}, author={Tang, Ming-Chun and Dang, Hoang X. and Lee, Sehyun and Barrit, Dounya and Munir, Rahim and Wang, Kai and Li, Ruipeng and Smilgies, Detlef-M. and De Wolf, Stefaan and Kim, Dong-Yu and et al.}, year={2021}, month={Mar}, pages={2000718} }
 @article{tang_fan_barrit_chang_dang_li_wang_smilgies_liu_de wolf_et al._2020, title={Ambient blade coating of mixed cation, mixed halide perovskites without dripping: in situ investigation and highly efficient solar cells}, volume={8}, ISSN={["2050-7496"]}, DOI={10.1039/c9ta12890e}, abstractNote={Blade coating of mixed cation, mixed halide perovskite films is investigated using in situ X-ray scattering to investigate the role of formulations and processing routes and eliminate the need for anti-solvent dripping.}, number={3}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={Tang, Ming-Chun and Fan, Yuanyuan and Barrit, Dounya and Chang, Xiaoming and Dang, Hoang X. and Li, Ruipeng and Wang, Kai and Smilgies, Detlef-M. and Liu, Shengzhong and De Wolf, Stefaan and et al.}, year={2020}, month={Jan}, pages={1095–1104} }
 @article{tang_fan_barrit_li_dang_zhang_magnanelli_nguyen_heilweil_hacker_et al._2020, title={Efficient Hybrid Mixed-Ion Perovskite Photovoltaics: In Situ Diagnostics of the Roles of Cesium and Potassium Alkali Cation Addition}, volume={4}, ISSN={["2367-198X"]}, DOI={10.1002/solr.202000272}, abstractNote={Perovskite photovoltaics have made extraordinary progress in power conversion efficiency (PCE) and stability due to process and formulation development. Perovskite cell performance benefits from the addition of alkali metal cations, such as cesium (Cs+) and potassium (K+) in mixed‐ion systems, but the underlying reasons are not fully understood. Herein, the solidification of perovskite layers is studied, incorporating 5%, 10%, to 20% of Cs+ and K+ using in situ grazing incidence wide‐angle X‐ray scattering. It is found that K+‐doped solutions yield nonperovskite 4H phase rather than the 3C perovskite phase. For Cs+‐doped formulations, both 4H and 3C phases are present at 5% Cs+, whereas the 3C perovskite phase is formed in 10% Cs+‐doped formulations, with undesirable halide segregation occurring at 20% Cs+. Postdeposition thermal annealing converts the intermediate 4H phase to the desirable 3C perovskite phase. Importantly, perovskite layers containing 5% of Cs+ or K+ exhibit a reduced concentration of trap states and enhanced carrier mobility and lifetime. By carefully adjusting Cs+ or K+ concentration to 5%, perovskite cells are demonstrated with a ≈5% higher‐average PCE than cells utilizing higher cation concentrations. Herein, unique insights into the crystallization pathways toward perovskite phase engineering and improved cell performance are provided.}, number={9}, journal={SOLAR RRL}, author={Tang, Ming-Chun and Fan, Yuanyuan and Barrit, Dounya and Li, Ruipeng and Dang, Hoang X. and Zhang, Siyuan and Magnanelli, Timothy J. and Nguyen, Nhan V. and Heilweil, Edwin J. and Hacker, Christina A. and et al.}, year={2020}, month={Sep} }
 @article{dang_wang_ghasemi_tang_de bastiani_aydin_dauzon_barrit_peng_smilgies_et al._2019, title={Multi-cation Synergy Suppresses Phase Segregation in Mixed-Halide Perovskites}, volume={3}, ISSN={["2542-4351"]}, DOI={10.1016/j.joule.2019.05.016}, abstractNote={Mixed lead halide perovskite solar cells have been demonstrated to benefit tremendously from the addition of Cs+ and Rb+, but its root cause is yet to be understood. This hinders further improvement, and processing approaches remain largely empirical. We address the challenge by tracking the solidification of precursors in situ and linking the evolutions of different crystalline phases to the presence of Cs+ and Rb+. In their absence, the perovskite film is inherently unstable, segregating into MA-I- and FA-Br-rich phases. Adding either Cs+ or Rb+ is shown to alter the solidification process of the perovskite films. The optimal addition of both Cs+ and Rb+ drastically suppress phase segregation and promotes the spontaneous formation of the desired α phase. We propose that the synergistic effect is due to the collective benefits of Cs+ and Rb+ on the formation kinetics of the α phase and on the halide distribution throughout the film.}, number={7}, journal={JOULE}, author={Dang, Hoang X. and Wang, Kai and Ghasemi, Masoud and Tang, Ming-Chun and De Bastiani, Michele and Aydin, Erkan and Dauzon, Emilie and Barrit, Dounya and Peng, Jun and Smilgies, Detlef-M and et al.}, year={2019}, month={Jul}, pages={1746–1764} }