Perylene diimide derivatives with different functional groups (OR) in the bay position were synthesised (PDI-1, OR = OC6H4OMe; PDI-2, OR = OC6H4CH2CH2NHBoc; PDI-3, OR = OC6H4CO2Me) and their optoelectronical properties...
Flexible perovskite solar cells triggered a vast interest within the scientific community, thanks to their broad commercialization prospects. However, the stability of these devices still poses one of the major concerns on the way to rapid industrial deployment. Here, we demonstrate an effective strategy to improve the technical aspects of this technology, improving the reliability and efficiency values of these devices. We apply large organic ammonium molecules for modifying a buried interface between a hole-transporting layer (HTL) and perovskiteabsorbing material. With the 4-fluorophenethylammonium iodide (FPEAI), we achieve 18.66% efficiency for the large-area (1 cm 2 ) flexible solar cell, a significant improvement over the pristine device without modification. The applied passivation strategy results in a better hole extraction and reduced nonradiative recombination loss at the buried interface. Moreover, we demonstrate the formation of low-dimensional perovskite phases in the vicinity of the hole-transporting material upon the incorporation of large ammonium cations. This results in a significantly enhanced thermal and light-soaking stability of fabricated devices. We obtained no loss in 1000 h of aging at 85 °C, no loss in 1000 h of light soaking at open circuit, and less than 10% drop in 1000 h of operation at maximum power point for the optimized passivation treatment with the FPEAI. We also demonstrate a method for monitoring the structural stability of perovskite thin films upon prolonged illumination, ensued by the amount of molecular iodine being released from the layer.
Photoreflectance measurements were performed for GaAs1−x−yNxBiy layers in the temperature range of 20–300 K. For each sample a transition related to the band-gap was observed, which red-shifts with increasing nitrogen and bismuth content. The temperature dependencies of the band-gap were fitted by the Varshni and Bose–Einstein formulas and simulated within the band anticrossing model of the interaction between the extended band states of the GaAs and the localized states associated with nitrogen and bismuth atoms. The reduction of the band-gap was found to be ∼80–100 meV.
BGaAs layers with boron concentrations of 4.1%, 7.4%, and 12.1% are grown by molecular beam epitaxy on a GaP substrate and studied by optical absorption and photoreflectance (PR) spectroscopy with both temperature and hydrostatic pressure dependence. The direct optical transitions from the bands composing the valence band—namely heavy-hole, light-hole, and spin–orbit split-off—to the conduction band are clearly observed in the PR spectra. For the abovementioned optical transitions, their temperature dependencies are obtained in the range from 20 K to 300 K, and analyzed by Varshni and Bose–Einstein relations. Furthermore, the BGaAs alloys are also studied with hydrostatic pressure up to ∼18 kbar, revealing pressure coefficients of direct optical transitions. The obtained results are discussed within the framework of the band anticrossing model and chemical trends.
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