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We present a simple yet powerful analysis of Suns‐photoluminescence quantum yield measurements that can be used to determine the surface saturation current densities of thin film semiconductors. We apply the method to state‐of‐the‐art polycrystalline perovskite thin films of varying absorber thickness. We show that the non‐radiative bimolecular recombination in these samples originates from the surfaces. To the best of our knowledge, this is the first study to demonstrate and quantify non‐linear (bimolecular) surface recombination in perovskite thin films. [ABSTRACT FROM AUTHOR]

Abstract Greater stability of low-dimensional halide perovskites as opposed to their three-dimensional counterparts, alongside their high extinction coefficient and thus excellent emission properties, have made them popular candidates for optoelectronic applications. Topological edges are found in two-dimensional perovskites that show distinct electronic properties. In this work, using Kelvin Probe Force Microscopy, performed on butylammonium lead bromide (BA2PbBr4) single crystals with optical bandgap of ~413 nm, we elucidate the electronic response of the edges and their potential impact on photodetector devices. We show that the charge-carriers are accumulated at the edges, increasing with the edge height. Wavelength-dependent surface photovoltage (SPV) measurements reveal that multiple sub-bandgap states exist in BA2PbBr4. As the edge height increases, the SPV amplitude at the edges reduces slightly more as compared to the adjacent regions, known as terraces, indicating relatively less reduction in band-bending at the surface due possibly to increased de-population of electrons from sub-bandgap states in the upper bandgap half. The existence of sub-bandgap states is further confirmed by the observation of below-bandgap emission (absorption) peaks characterised by spectral photoluminescence and photothermal deflection spectroscopy measurements. Finally, we fabricated a photodetector using a millimetre size BA2PbBr4 single crystal. Noticeable broadband photodetection response was observed in the sub-bandgap regions under green and red illumination, which is attributed to the existence of sub-bandgap states. Our observations suggest edge-height dependence of charge-carrier behaviour in BA2PbBr4 single crystals, a potential pathway that can be exploited for efficient broadband photodetector fabrication.

Carrot pomace (CP) which is generated in a large volume in the juice production process, is rich in cellulose, hemicellulose, sugars, pectin, and minerals. However, in many previous investigations, only cellulose was purified and utilized while other components of CP were discarded as waste. Here, CP was valorized into fungal biomass and cellulose with the aim of utilizing all the CP components. Enzymatic pretreatments were applied to solubilize the digestible fraction of CP including hemicellulose, pectin, sucrose, and other sugars for fungal cultivation, while cellulose remained intact in the solid fraction. The dissolved fraction was utilized as a substrate for the cultivation of an edible fungus (Rhizopus delemar). Fungal cultivation was performed in shake flasks and bench-scale bioreactors. The highest fungal biomass concentration was obtained after pretreatment with invertase (5.01 g/L) after 72 h of cultivation (36 and 42% higher than the concentrations obtained after hemicellulase and pectinase treatments, respectively). Invertase pretreatment resulted in the hydrolysis of sucrose, which could then be taken up by the fungus. Carbohydrate analysis showed 28–33% glucan, 4.1–4.9% other polysaccharides, 0.01% lignin, and 2.7–7% ash in the CP residues after enzymatic pretreatment. Fourier transform infrared spectroscopy and thermogravimetric analysis also confirmed the presence of cellulose in this fraction. The obtained fungal biomass has a high potential for food or feed applications, or as a raw material for the development of biomaterials. Cellulose could be purified from the solid fraction and used for applications such as biobased-textiles or membranes for wastewater treatment, where pure cellulose is needed.

The organic spacer cation plays a crucial role in determining the exciton fine structure in 2D perovskites. Here, magneto‐optical spectroscopy is used to gain insight into the influence of the organic spacer on dark excitons in Ruddlesden–Popper (RP) perovskites. Using modest magnetic field strengths (<1.5 T), the optically forbidden dark exciton state can be identified and its emission properties significantly modulated via application of in‐plane magnetic fields, up to temperatures of 15 K. At low temperatures, an increase in collected photoluminescence efficiency of >30% is demonstrated, signifying the critical role of the dark exciton state for light‐emitting applications of 2D perovskites. The exciton fine structure and the degree of magnetic‐field‐induced mixing are significantly impacted by the choice of organic spacer cation, with 4–methoxyphenylethylammonium (MeO‐PEA) showing the largest effect due to larger bright–dark exciton splitting. This study distinguishes between interior (bulk) and surface dark‐exciton emission, showing that bright–dark exciton splitting differs between the interior and surface. The results emphasize the significance of the organic spacer cation in controlling the exciton fine structure in 2D perovskites and have important implications for the development of optoelectronic technology based on 2D perovskites. [ABSTRACT FROM AUTHOR]

Long‐chain organic halide salts are widely used in perovskite‐based optoelectronic devices for surface passivation owing to their capability to interact with the surface defects of perovskites. Here, aluminum oxide (AlOx) is introduced via atomic layer deposition onto octylammonium iodide (OAI) to exploit the benefits of organic halide salts without generating undesired defects. The devices incorporating AlOx on OAI‐treated perovskite (OAI/AlOx) show enhancement in both device performance and photo‐stability compared to those with only treatment. A diffusion of aluminum from AlOx into the perovskite through surface characterization contributes to a uniform photo‐generated carrier transport in both the surface and the bulk of the perovskite absorber. In addition, it is revealed that light‐induced two‐dimensional perovskite formation on OAI/AlOx. This may be ascribed to preventing the loss of OA cations due to the presence of AlOx, leading to a decrease in the number of iodine anions which suppresses the light‐induced degradation of corresponding devices. Consequently, the devices show over 24% efficiency and retain their efficiency over 1000 hours under continuous light illumination. [ABSTRACT FROM AUTHOR]

A novel, camera‐based method for direct implied open‐circuit voltage (iVOC) imaging via the use of a single bandpass filter (s‐BPF) is developed for large‐area photovoltaic solar cells and precursors. The photoluminescence (PL) emission is imaged using a narrow BPF with centre energy inside the high‐energy tail of the PL emission, utilising the close‐to‐unity and nearly constant absorptivity of typical photovoltaic devices in this energy range. As a result, the exact value of the sample's absorptivity within the BPF transmission band is not required. The use of an s‐BPF enables a fully contactless approach to calibrate the absolute PL photon flux for spectrally integrated detectors, including cameras. The method eliminates the need for knowledge of the imaging system spectral response. Through an appropriate choice of the BPF centre energy, a range of absorber compositions or a single absorber with different surface morphologies, such as planar and textured, can be imaged, all without the need for additional detection optics. The feasibility of this s‐BPF method is first validated. The relative error in iVOC is determined to be ≤1.5%. The method is then demonstrated on device stacks with two different perovskite compositions commonly used in single‐junction and monolithic tandem solar cells. [ABSTRACT FROM AUTHOR]