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Browsing Chemistry - Publications by Author "Abdelhady, Ahmed L."
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    CH < inf > 3 < /inf > NH < inf > 3 < /inf > PbCl < inf > 3 < /inf > Single Crystals: Inverse Temperature Crystallization and Visible-Blind UV-Photodetector
    ( 2015-10-01) Maculan, Giacomo ; Sheikh, Arif D. ; Abdelhady, Ahmed L. ; Saidaminov, Makhsud I. ; Haque, Md Azimul ; Murali, Banavoth ; Alarousu, Erkki ; Mohammed, Omar F. ; Wu, Tom ; Bakr, Osman M.
    Single crystals of hybrid perovskites have shown remarkably improved physical properties compared to their polycrystalline film counterparts, underscoring their importance in the further development of advanced semiconductor devices. Here we present a new method of growing sizable CH3NH3PbCl3 single crystals based on the retrograde solubility behavior of hybrid perovskites. We show, for the first time, the energy band structure, charge recombination, and transport properties of CH3NH3PbCl3 single crystals. These crystals exhibit trap-state density, charge carrier concentration, mobility, and diffusion length comparable with the best quality crystals of methylammonium lead iodide or bromide perovskites reported so far. The high quality of the crystal along with its suitable optical band gap enabled us to build an efficient visible-blind UV-photodetector, demonstrating its potential in optoelectronic applications.
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    Engineering interfacial charge transfer in CsPbBr < inf > 3 < /inf > perovskite nanocrystals by heterovalent doping
    ( 2017-01-18) Begum, Raihana ; Parida, Manas R. ; Abdelhady, Ahmed L. ; Murali, Banavoth ; Alyami, Noktan M. ; Ahmed, Ghada H. ; Hedhili, Mohamed Nejib ; Bakr, Osman M. ; Mohammed, Omar F.
    Since compelling device efficiencies of perovskite solar cells have been achieved, investigative efforts have turned to understand other key challenges in these systems, such as engineering interfacial energy-level alignment and charge transfer (CT). However, these types of studies on perovskite thin-film devices are impeded by the morphological and compositional heterogeneity of the films and their ill-defined surfaces. Here, we use well-defined ligand-protected perovskite nanocrystals (NCs) as model systems to elucidate the role of heterovalent doping on charge-carrier dynamics and energy level alignment at the interface of perovskite NCs with molecular acceptors. More specifically, we develop an in situ doping approach for colloidal CsPbBri perovskite NCs with heterovalent Bi3+ ions bv hot injection to precisely tune their band structure and excited-state dynamics. This synthetic method allowed us to map the impact of doping on CT from the NCs to different molecular acceptors. Using time-resolved spectroscopy with broadband capability, we clearly demonstrate that CT at the interface of NCs can be tuned and promoted by metal ion doping. We found that doping increases the energy difference between states of the molecular acceptor and the donor moieties, subsequently facilitating the interfacial CT process. This work highlights the key variable components not only for promoting interfacial CT in perovskites, but also for establishing a higher degree of precision and control over the surface and the interface of perovskite molecular acceptors.
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    Formamidinium Lead Halide Perovskite Crystals with Unprecedented Long Carrier Dynamics and Diffusion Length
    ( 2016-07-08) Zhumekenov, Ayan A. ; Saidaminov, Makhsud I. ; Haque, Md Azimul ; Alarousu, Erkki ; Sarmah, Smritakshi Phukan ; Murali, Banavoth ; Dursun, Ibrahim ; Miao, Xiao He ; Abdelhady, Ahmed L. ; Wu, Tom ; Mohammed, Omar F. ; Bakr, Osman M.
    State-of-the-art perovskite solar cells with record efficiencies were achieved by replacing methylammonium (MA) with formamidinium (FA) in perovskite polycrystalline films. However, these films suffer from severe structural disorder and high density of traps; thus, the intrinsic properties of FA-based perovskites remain obscured. Here we report the detailed optical and electrical properties of FAPbX3 (where X = Br- and I-) single crystals. FAPbX3 crystals exhibited markedly enhanced transport compared not just to FAPbX3 polycrystalline films but also, surprisingly, to MAPbX3 single crystals. Particularly, FAPbBr3 crystals displayed a 5-fold longer carrier lifetime and 10-fold lower dark carrier concentration than those of MAPbBr3 single crystals. We report long carrier diffusion lengths - much longer than previously thought - of 6.6 μm for FAPbI3 and 19.0 μm for FAPbBr3 crystals, the latter being one of the longest reported values in perovskite materials. These findings are of great importance for future integrated applications of these perovskites.
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    Heterovalent Dopant Incorporation for Bandgap and Type Engineering of Perovskite Crystals
    ( 2016-01-21) Abdelhady, Ahmed L. ; Saidaminov, Makhsud I. ; Murali, Banavoth ; Adinolfi, Valerio ; Voznyy, Oleksandr ; Katsiev, Khabiboulakh ; Alarousu, Erkki ; Comin, Riccardo ; Dursun, Ibrahim ; Sinatra, Lutfan ; Sargent, Edward H. ; Mohammed, Omar F. ; Bakr, Osman M.
    Controllable doping of semiconductors is a fundamental technological requirement for electronic and optoelectronic devices. As intrinsic semiconductors, hybrid perovskites have so far been a phenomenal success in photovoltaics. The inability to dope these materials heterovalently (or aliovalently) has greatly limited their wider utilizations in electronics. Here we show an efficient in situ chemical route that achieves the controlled incorporation of trivalent cations (Bi3+, Au3+, or In3+) by exploiting the retrograde solubility behavior of perovskites. We term the new method dopant incorporation in the retrograde regime. We achieve Bi3+ incorporation that leads to bandgap tuning (∼300 meV), 104 fold enhancement in electrical conductivity, and a change in the sign of majority charge carriers from positive to negative. This work demonstrates the successful incorporation of dopants into perovskite crystals while preserving the host lattice structure, opening new avenues to tailor the electronic and optoelectronic properties of this rapidly emerging class of solution-processed semiconductors.
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    High-quality bulk hybrid perovskite single crystals within minutes by inverse temperature crystallization
    ( 2015-07-06) Saidaminov, Makhsud I. ; Abdelhady, Ahmed L. ; Murali, Banavoth ; Alarousu, Erkki ; Burlakov, Victor M. ; Peng, Wei ; Dursun, Ibrahim ; Wang, Lingfei ; He, Yao ; MacUlan, Giacomo ; Goriely, Alain ; Wu, Tom ; Mohammed, Omar F. ; Bakr, Osman M.
    Single crystals of methylammonium lead trihalide perovskites (MAPbX < inf > 3 < /inf > ; MA=CH < inf > 3 < /inf > NH < inf > 3 < /inf > < sup > + < /sup > , X=Br < sup > - < /sup > or I < sup > - < /sup > ) have shown remarkably low trap density and charge transport properties; however, growth of such high-quality semiconductors is a time-consuming process. Here we present a rapid crystal growth process to obtain MAPbX < inf > 3 < /inf > single crystals, an order of magnitude faster than previous reports. The process is based on our observation of the substantial decrease of MAPbX < inf > 3 < /inf > solubility, in certain solvents, at elevated temperatures. The crystals can be both size-and shape-controlled by manipulating the different crystallization parameters. Despite the rapidity of the method, the grown crystals exhibit transport properties and trap densities comparable to the highest quality MAPbX < inf > 3 < /inf > reported to date. The phenomenon of inverse or retrograde solubility and its correlated inverse temperature crystallization strategy present a major step forward for advancing the field on perovskite crystallization.
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    Robust and air-stable sandwiched organo-lead halide perovskites for photodetector applications
    ( 2016-01-01) Murali, Banavoth ; Saidaminov, Makhsud I. ; Abdelhady, Ahmed L. ; Peng, Wei ; Liu, Jiakai ; Pan, Jun ; Bakr, Osman M. ; Mohammed, Omar F.
    We report the simplest possible method to date for fabricating robust, air-stable, sandwiched perovskite photodetectors. Unlike conventionally designed photodetectors, our proposed sandwiched structure does not require electron/hole transporting layers or expensive electrodes. We demonstrate that photocurrent and sensitivity are enhanced by an order of magnitude in the MAPbI3-MAPbBr3 heterojunction compared to the homojunctions of their analogues. This simpler approach may have applications in the perovskite-only class of solar cells with the goal of scaling up towards commercialization.
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    Surface Restructuring of Hybrid Perovskite Crystals
    ( 2016-12-09) Murali, Banavoth ; Dey, Sukumar ; Abdelhady, Ahmed L. ; Peng, Wei ; Alarousu, Erkki ; Kirmani, Ahmad R. ; Cho, Namchul ; Sarmah, Smritakshi Phukan ; Parida, Manas R. ; Saidaminov, Makhsud I. ; Zhumekenov, Ayan A. ; Sun, Jingya ; Alias, Mohd S. ; Yengel, Emre ; Ooi, Boon S. ; Amassian, Aram ; Bakr, Osman M. ; Mohammed, Omar F.
    Hybrid perovskite crystals have emerged as an important class of semiconductors because of their remarkable performance in optoelectronics devices. The interface structure and chemistry of these crystals are key determinants of the device's performance. Unfortunately, little is known about the intrinsic properties of the surfaces of perovskite materials because extrinsic effects, such as complex microstructures, processing conditions, and hydration under ambient conditions, are thought to cause resistive losses and high leakage current in solar cells. We reveal the intrinsic structural and optoelectronic properties of both pristinely cleaved and aged surfaces of single crystals. We identify surface restructuring on the aged surfaces (visualized on the atomic-scale by scanning tunneling microscopy) that lead to compositional and optical bandgap changes as well as degradation of carrier dynamics, photocurrent, and solar cell device performance. The insights reported herein clarify the key variables involved in the performance of perovskite-based solar cells and fabrication of high-quality surface single crystals, thus paving the way toward their future exploitation in highly efficient solar cells.