Yu, Weili; Noureldine, Dalal; Isimjan, Tayirjan T.; Bin, Lin; Del Gobbo, Silvano; Abulikemu, Mutalifu; Hedhili, Mohamed N.; Anjum, Dalaver H.; Takanabe, Kazuhiro(Phys. Chem. Chem. Phys., Royal Society of Chemistry (RSC), 2015)[Article]
Efficient photocatalytic hydrogen generation in a suspension system requires a sophisticated nano-device that combines a photon absorber with effective redox catalysts. This study demonstrates an innovative molecular linking strategy for fabricating photocatalytic materials that allow effective charge separation of excited carriers, followed by efficient hydrogen evolution. The method for the sequential replacement of ligands with appropriate molecules developed in this study tethers both quantum dots (QDs), as photosensitizers, and metal nanoparticles, as hydrogen evolution catalysts, to TiO2 surfaces in a controlled manner at the nano-level. Combining hydrophobic and hydrophilic interactions on the surface, CdSe-ZnS core-shell QDs and an Au-Pt alloy were attached to TiO2 without overlapping during the synthesis. The resultant nano-photocatalysts achieved substantially high-performance visible-light-driven photocatalysis for hydrogen evolution. All syntheses were conducted at room temperature and in ambient air, providing a promising route for fabricating visible-light-responsive photocatalysts.
Bootharaju, Megalamane Siddaramappa; Kozlov, Sergey; Cao, Zhen; Harb, Moussab; Parida, Manas R.; Hedhili, Mohamed N.; Mohammed, Omar F.; Bakr, Osman; Cavallo, Luigi; Basset, Jean-Marie(Nanoscale, Royal Society of Chemistry (RSC), 2017-06-07)[Article]
Heteroatom doping of atomically precise nanoclusters (NCs) often yields a mixture of doped and undoped products of single-atom difference, whose separation is extremely difficult. To overcome this challenge, novel synthesis methods are required to offer monodisperse doped NCs. For instance, the direct synthesis of PtAg28 NCs produces a mixture of [Ag29(BDT)12(TPP)4]3- and [PtAg28(BDT)12(TPP)4]4- NCs (TPP: triphenylphosphine; BDT: 1,3-benzenedithiolate). Here, we designed a ligand-exchange (LE) strategy to synthesize single-sized, Pt-doped, superatomic Ag NCs [PtAg28(BDT)12(TPP)4]4- by LE of [Pt2Ag23Cl7(TPP)10] NCs with BDTH2 (1,3-benzenedithiol). The doped NCs were thoroughly characterized by optical and photoelectron spectroscopy, mass spectrometry, total electron count, and time-dependent density functional theory (TDDFT). We show that the Pt dopant occupies the center of the PtAg28 cluster, modulates its electronic structure and enhances its photoluminescence intensity and excited-state lifetime, and also enables solvent interactions with the NC surface. Furthermore, doped NCs showed unique reactivity with metal ions - the central Pt atom of PtAg28 could not be replaced by Au, unlike the central Ag of Ag29 NCs. The achieved synthesis of single-sized PtAg28 clusters will facilitate further applications of the LE strategy for the exploration of novel multimetallic NCs.
Ahmed, Ghada H.; Yin, Jun; Bose, Riya; Sinatra, Lutfan; Alarousu, Erkki; Yengel, Emre; AlYami, Noktan Mohammed; Saidaminov, Makhsud I.; Zhang, Yuhai; Hedhili, Mohamed N.; Bakr, Osman; Bredas, Jean-Luc; Mohammed, Omar F.(Chemistry of Materials, American Chemical Society (ACS), 2017-05-02)[Article]
Engineering the surface energy through careful manipulation of the surface chemistry is a convenient approach to control quantum confinement and structure dimensionality during nanocrystal growth. Here, we demonstrate that the introduction of pyridine during the synthesis of methylammonium lead bromide (MAPbBr) perovskite nanocrystals can transform three-dimensional (3D) cubes into two-dimensional (2D) nanostructures. Density functional theory (DFT) calculations show that pyridine preferentially binds to Pb atoms terminating the surface, driving the selective 2D growth of the nanostructures. These 2D nanostructures exhibit strong quantum confinement effects, high photoluminescence quantum yields in the visible spectral range, and efficient charge transfer to molecular acceptors. These qualities indicate the suitability of the synthesized 2D nanostructures for a wide range of optoelectronic applications.
Parasitic absorption in transparent electrodes is one of the main roadblocks to enabling power conversion efficiencies (PCEs) for perovskite-based tandem solar cells beyond 30%. To reduce such losses and maximize light coupling, the broadband transparency of such electrodes should be improved, especially at the front of the device. Here, the excellent properties of Zr-doped indium oxide (IZRO) transparent electrodes for such applications, with improved near-infrared (NIR) response, compared to conventional tin-doped indium oxide (ITO) electrodes, are shown. Optimized IZRO films feature a very high electron mobility (up to ≈77 cm2 V−1 s−1), enabling highly infrared transparent films with a very low sheet resistance (≈18 Ω −1 for annealed 100 nm films). For devices, this translates in a parasitic absorption of only ≈5% for IZRO within the solar spectrum (250–2500 nm range), to be compared with ≈10% for commercial ITO. Fundamentally, it is found that the high conductivity of annealed IZRO films is directly linked to promoted crystallinity of the indium oxide (In2O3) films due to Zr-doping. Overall, on a four-terminal perovskite/silicon tandem device level, an absolute 3.5 mA cm−2 short-circuit current improvement in silicon bottom cells is obtained by replacing commercial ITO electrodes with IZRO, resulting in improving the PCE from 23.3% to 26.2%.
Bootharaju, Megalamane Siddaramappa; Kozlov, Sergey; Cao, Zhen; Harb, Moussab; Maity, Niladri; Shkurenko, Aleksander; Parida, Manas R.; Hedhili, Mohamed N.; Eddaoudi, Mohamed; Mohammed, Omar F.; Bakr, Osman; Cavallo, Luigi; Basset, Jean-Marie(Journal of the American Chemical Society, American Chemical Society (ACS), 2017-01-12)[Article]
Atomically precise self-assembled architectures of noble metals with unique surface structures are necessary for prospective applications. However, the synthesis of such structures based on silver is challenging because of their instability. In this work, by developing a selective and controlled doping strategy, we synthesized and characterized a rod-shaped, charge-neutral, diplatinum-doped Ag nanocluster (NC) of [Pt2Ag23Cl7(PPh3)10]. Its crystal structure revealed the self-assembly of two Pt-centered Ag icosahedra through vertex sharing. Five bridging and two terminal chlorides and 10 PPh3 ligands were found to stabilize the cluster. Electronic structure simulations corroborated structural and optical characterization of the cluster and provided insights into the effect of the Pt dopants on the optical properties and stability of the cluster. Our study will open new avenues for designing novel self-assembled NCs using different elemental dopants.
Begum, Raihana; Parida, Manas R.; Abdelhady, Ahmed L.; Banavoth, Murali; AlYami, Noktan Mohammed; Ahmed, Ghada H.; Hedhili, Mohamed N.; Bakr, Osman; Mohammed, Omar F.(Journal of the American Chemical Society, American Chemical Society (ACS), 2016-12-30)[Article]
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 CsPbBr3 perovskite NCs with heterovalent Bi3+ ions by 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.
A two-step ligand-exchange strategy is developed, in which the long-carbon-chain ligands on all-inorganic perovskite (CsPbX3, X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-paircapped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.
Ahmed, Ghada H.; Liu, Jiakai; Parida, Manas R.; Banavoth, Murali; Bose, Riya; AlYami, Noktan Mohammed; Hedhili, Mohamed N.; Peng, Wei; Pan, Jun; Besong, Tabot M.D.; Bakr, Osman; Mohammed, Omar F.(The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2016-09-22)[Article]
Hybrid organic/inorganic perovskites have recently emerged as an important class of materials and have exhibited remarkable performance in photovoltaics. To further improve their device efficiency, an insightful understanding of the interfacial charge transfer (CT) process is required. Here, we report the first direct experimental observation of the tremendous effect that the shape of perovskite nanocrystals (NCs) has on interfacial CT in the presence of a molecular acceptor. A dramatic change in CT dynamics at the interfaces of three different NC shapes, spheres, platelets, and cubes, is recorded. Our results clearly demonstrate that the mechanism of CT is significantly affected by the NC shape. More importantly, the results demonstrate that complexation on the NC surface acts as an additional driving force not only to tune the CT dynamics but also to control the reaction mechanism at the interface. This observation opens a new venue for further developing perovskite NCs-based applications.
El Tall, Omar; Hou, Yuanfang; Abou-Hamad, Edy; Raja, Inam Ul haq; Hedhili, Mohamed N.; Peng, Wei; Mahfouz, Remi; Bakr, Osman; Beaujuge, Pierre(Chemistry of Materials, American Chemical Society (ACS), 2014-04-21)[Article]
Diamond materials span a wide range of attractive physical properties, including large mechanical resistance, high thermal conductivity, and tunable optoelectronic behavior when suitably doped. Down to the nanoscale, embedded diamond nanoparticles find use in surface coatings and nanocomposites and are promising building elements in nanophotonic device engineering. The nature of the solubilizing substituents and specific functional groups appended to the nanodiamond surface defines the function of the nanoparticle and in turn its field of applicability. Synthetic nanodiamonds prepared by detonation protocols, so-called detonation diamond nanoparticles (DDNP), are composed of primary nanocrystals (2-10 nm) and their aggregates. A detailed experimental section can be found in the Supporting Information; the XRD analysis of the GDNP(800) precursor confirmed the integrity of the diamond core upon thermal annealing.
We demonstrate that ultrathin P-type Cu2O thin films fabricated by a facile thermal oxidation method can serve as a promising hole-transporting material in perovskite solar cells. Following a two-step method, inorganic-organic hybrid perovskite solar cells were fabricated and a power conversion efficiency of 11.0% was achieved. We find that the thickness and properties of Cu2O layers must be precisely tuned in order to achieve the optimal solar cell performance. The good performance of such perovskite solar cells can be attributed to the unique properties of ultrathin Cu2O, including high hole mobility, good energy level alignment with CH3NH3PbI3, and longer lifetime of photo-excited carriers. Combining merits of low cost, facile synthesis, and high device performance, ultrathin Cu2O films fabricated via thermal oxidation hold promise for facilitating the developments of industrial-scale perovskite solar cells.
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