Ahmed Esmail Shalan

Concordantly fabricated heterojunction ZnO–TiO2 nanocomposite electrodes via a co-precipitation method for efficient stable quasi-solid-state dye-sensitized solar cells

This manuscript is concerned with the successful attempts we have made to fabricate nanostructured spheres composed of mixed metal oxides. ZnO/TiO2 nanocomposites supported on an FTO substrate are used as the photoanode electrode for quasi-solid-state dye-sensitized solar cells (QS-DSSCs). The phase purity of the ZnO and TiO2 phases of the composite shell has been studied by X-ray diffraction peak analysis. A novel gel polymer electrolyte based on a poly(acrylamide)–poly(ethylene glycol) composite and a binary organic solvent was prepared. The polymer gel electrolyte based on the composite of poly(acrylamide)–poly(ethylene glycol), the binary organic solvent of ethylene carbonate and propylene carbonate and the additive of 4-tert-butylpyridine has been employed to fabricate a quasi-solid-state dye-sensitized solar cell. The conversion efficiency of the dye-sensitized solar cells with nanocomposites is 6.5% which is more than double compared with that of bare ZnO nanoparticle photoanodes (3.8%). We believe that this improvement comes from the synergetic effect between ZnO and TiO2, which increases dye absorption, electron transport and electron lifetime, as discussed with the EIS and loaded absorption results. From the current–voltage and incident photon-to-current conversion efficiency (IPCE) measurement, the conductivity of the nanocomposite ZnO–TiO2 was shown to be higher compared to the nanostructured ZnO itself. This simple method can be universally adopted for all quasi-solid-state electrolyte-based DSSCs in order to improve their performance and durability.

Copper-Substituted Lead Perovskite Materials Constructed with Different Halides for Working (CH3NH3)2CuX4-Based Perovskite Solar Cells from Experimental and Theoretical View

Toxicity and chemical instability issues of halide perovskites based on organic-inorganic lead-containing materials still remain as the main drawbacks for perovskite solar cells (PSCs). Herein, we discuss the preparation of copper (Cu)-based hybrid materials, where we replace lead (Pb) with nontoxic Cu metal for lead-free PSCs, and investigate their potential toward solar cell applications based on experimental and theoretical studies. The formation of (CH3NH3)2CuX4 [(CH3NH3)2CuCl4, (CH3NH3)2CuCl2I2, and (CH3NH3)2CuCl2Br2] was discussed in details. Furthermore, it was found that chlorine (Cl-) in the structure is critical for the stabilization of the formed compounds. Cu-based perovskite-like materials showed attractive absorbance features extended to the near-infrared range, with appropriate band gaps. Green photoluminescence of these materials was obtained because of Cu+ ions. The power conversion efficiency was measured experimentally and estimated theoretically for different architectures of solar cell devices.

Optimization of a compact layer of TiO2via atomic-layer deposition for high-performance perovskite solar cells

We report the effect of thickness of a film consisting of a compact layer of TiO2 produced via atomic-layer deposition (ALD) for mesoporous perovskite solar cells (PSCs) with a n-i-p configuration. Uniform and pinhole-free TiO2 films of thickness from 10 to 400 nm were deposited on fluorine-doped tin-oxide substrates using ALD. The device performance of the PSC showed a trend systematic with the thickness of the ALD-TiO2 compact layer and attained the best efficiency, 15.0%, of power conversion at thickness 200 nm. Photoluminescence (PL) spectra and the corresponding PL decays for perovskite (PSK) deposited on varied ALD-TiO2 films were recorded; the effective PL quenching is due to electron transfer from PSK into the ALD-TiO2 compact layer. The most efficient interfacial electron transfer occurred at film thickness 200 nm, for which the ALD-TiO2 film has the greatest surface roughness and conductivity. We found a systematic correlation between the device performance in relation to the conductivity and the rate of interfacial electron transfer as a function of thickness of the ALD-TiO2 film; the best performance occurred at thickness 200 nm. The devices showed great stability and reproducibility, providing an alternative for high-performance PSCs with a well-controlled TiO2 compact layer.

Solid-state dye-sensitized solar cells based on Zn1−xSnxO nanocomposite photoanodes

Solid-state dye-sensitized solar cells (ss-DSSCs) comprising Sn2+-substituted ZnO nanopowder were purposefully tailored via a co-precipitation method. The solar cells assembled in this work were sensitized with N719 ruthenium dye and insinuated with spiro-OMeTAD as a solid hole transport layer (HTL). Evidently, significant enhancement in cell efficiency was accomplished with Sn2+ ions-substituted ZnO photoelectrodes by maintaining the weight ratio of SnO at 5%. The overall power conversion efficiency was improved from 3.0% for the cell with pure ZnO to 4.3% for the cell with 5% SnO substitution. The improvement in the cell efficiency with Sn2+-substituted ZnO photoelectrodes is attributed to the considerably large surface area of the nanopowders for dye adsorption, efficient charge separation and the suppression of charge recombination provided by SnO. Furthermore, the energy distinction between the conduction band edges of SnO and ZnO implied a type II band alignment. Moreover, the durability as well as the stability of 15 assembled cells were studied to show the outstanding long-term stability of the devices made of Sn2+ ion substituted ZnO, and the PCE of each cell remained stable and ∼96% of its primary value was retained for up to 100 h. Subsequently, the efficacy was drastically reduced to ∼35% after 250 h of storage.