Issam Gereige

Highly Transparent and UV-Resistant Superhydrophobic SiO2-Coated ZnO Nanorod Arrays

Highly transparent and UV-resistant superhydrophobic arrays of SiO2-coated ZnO nanorods are prepared in a sequence of low-temperature (<150 °C) steps on both glass and thin sheets of PET (2 × 2 in.2), and the superhydrophobic nanocomposite is shown to have minimal impact on solar cell device performance under AM1.5G illumination. Flexible plastics can serve as front cell and backing materials in the manufacture of flexible displays and solar cells.

Ultralong Radiative States in Hybrid Perovskite Crystals: Compositions for Submillimeter Diffusion Lengths

Organic-inorganic hybrid perovskite materials have recently evolved into the leading candidate solution-processed semiconductor for solar cells due to their combination of desirable optical and charge transport properties. Chief among these properties is the long carrier diffusion length, which is essential to optimizing the device architecture and performance. Herein, we used time-resolved photoluminescence (at low excitation fluence, 10.59 μJ·cm-2 upon two-photon excitation), which is the most accurate and direct approach to measure the radiative charge carrier lifetime and diffusion lengths. Lifetimes of about 72 and 4.3 μs for FAPbBr3 and FAPbI3 perovskite single crystals have been recorded, presenting the longest radiative carrier lifetimes reported to date for perovskite materials. Subsequently, carrier diffusion lengths of 107.2 and 19.7 μm are obtained. In addition, we demonstrate the key role of the organic cation units in modulating the carrier lifetime and its diffusion lengths, in which the defect formation energies for FA cations are much higher than those with the MA ones.

CsPb2Br5 Single Crystals: Synthesis and Characterization

CsPb2 Br5 is a ternary halogen-plumbate material with close characteristics to the well-reported halide perovskites. Owing to its unconventional two-dimensional structure, CsPb2 Br5 is being looked at broadly for potential applications in optoelectronics. CsPb2 Br5 investigations are currently limited to nanostructures and powder forms of the material, which present unclear and conflicting optical properties. In this study, we present the synthesis and characterization of CsPb2 Br5 bulk single crystals, which enabled us to finally clarify the materials optical features. Our CsPb2 Br5 crystal has a two-dimensional structure with Pb2 Br5- layers spaced by Cs+ cations, and exhibits approximately 3.1u2005eV indirect band gap with no emission in the visible spectrum.

Improving Uniformity and Reproducibility of Hybrid Perovskite Solar Cells via a Low-Temperature Vacuum Deposition Process for NiOx Hole Transport Layers

Recently, the trend in inverted hybrid perovskite solar cells (PVSCs) has been to utilize NiOx as hole transport layers. However, the majority of reported solution-processed NiOx films require a high-temperature thermal annealing process, which is unfavorable for large-scale manufacturing and suffers from lack of uniformity. We report, for the first time, e-beam evaporation as a low-temperature vacuum process for the deposition of NiOx hole transport layers for PVSCs. Device characterization shows that efficiency is on par with solution-processed methods, the highest efficiency at 15.4% with no obvious hysteresis. Differences are found to be due to the presence of more Ni3+ in e-beam evaporated NiOx, which are responsible for a lower transmittance but higher conductivity. Most importantly, e-beam-evaporated NiOx-based PVSCs show greater uniformity and reproducibility compared to spin-coated NiOx-based PVSCs. Finally, e-beam-evaporated NiOx has the additional advantage of being produced by a low-temperature deposition process and applicable over large areas. This work, therefore, represents a significant step toward large-area PVSCs, where e-beam evaporation can be used for the low-temperature uniform deposition of charge-transport layers, such as NiOx.

Understanding effects of precursor solution aging in triple cation lead perovskite

The solution process is the most widely used method to prepare perovskite absorbers for high performance solar cells due to its ease for fabrication and low capital cost. However, an insufficient level of reproducibility of the solution process is often a concern. Complex precursor solution chemistry is likely one of the main reasons for the reproducibility issue. Here we report the effects of triple cation lead mixed-halide perovskite precursor solution aging on the quality of the resulting films and the device performance. Our study revealed that precursor solution aging has a great influence on the colloidal size distribution of the solution, which then affects the phase purity of the films and device performance. We determined the optimum aging hours that led to the best device efficiency along with the highest reproducibility. Dynamic light scattering revealed the formation of micron-sized colloidal intermediates in the solution when aged longer than the optimum hours and further analysis along with X-ray diffraction measurements suggested there were two chemical origins of the large aggregates, FA-based and Cs-based complexes.