Muhammad Shahriar Bashar

Photosynthetic microbial fuel cells (PMFCs) represent an emerging class of bio-electrochemical systems capable of converting organic pollutants into electricity through microbial catalysis.

Mixed-cation lead bromideperovskitethin filmsandpowderswithcompositionHA(1-𝑥)MA𝑥PbBr3(𝑥 = 0.0, 0.20, 0.40) were synthesised via solution-processed spin-coating and comprehensivelycharacterised to elucidate the role of methylammonium (MA+) incorporation in hydrazinium(HA+) lead bromide perovskites. XRD analysis revealed a progressive hexagonal-to-tetragonalphase transition with increasing MA+ content, accompanied by crystallite size reduction from86.68 ± 5.99 nm to 61.26 ± 11.59 nm and concurrent increases in dislocation density andmicrostrain. SEMconfirmedmorphologicalevolutionfromagglomeratednanoparticles(88.61±23.43 nm) in pristine HAPbBr3 to a refined homogeneous nanostructure (72.41 ± 16.40 nm) inHA0.6MA0.4PbBr3, while EDX confirmed stoichiometric compositions and successful A-sitecation mixing. FTIR and Raman spectroscopy verified co-incorporation of both cations withinthe intact PbBr4-6 octahedral framework. UV–Vis spectrophotometry revealed direct bandgapsof 2.9565, 2.9339, and 2.3075 eV for 𝑥 = 0, 0.20, and 0.40, respectively, demonstratingcontinuous bandgap tunability via a two-stage mechanism of chemical A-site perturbationand phase-transition-driven bandgap collapse. Urbach energy decreased monotonically from0.2112 to 0.1902 eV, indicating progressive band-edge quality improvement. Hall effectmeasurements showed carrier mobility increasing from 71.86 to 143.2 cm2 V-1 s-1 andconductivity from 1.078 × 10-5 to 2.278 × 10-5 Ω-1 cm-1 for HA0.6MA0.4PbBr3. Usingexperimentally determined parameters, seventeen solar-cell architectures (SC1–SC17) wereevaluated by SCAPS-1D simulation, employing HAPbBr3 and HA0.8MA0.2PbBr3 as electrontransport layers and HA0.6MA0.4PbBr3 as the absorber layer. The highest PCE of 32.18% wasachieved by Cs2InSbCl6-based devices (SC3 and SC8) with NiO hole transport layers, whileHA0.6MA0.4PbBr3 single-absorber cells (SC11–SC13) attained the highest fill factors (>82%)among all architectures. Temperature (300–420 K) and back-contact work function (4.8–6.0 eV)analyses confirmed the thermal robustness and contact tolerance of the devices, establishingHA(1-𝑥)MA𝑥PbBr3 as a promising candidate for next-generation tandem photovoltaic applications.

Nanostructured copper oxide (CuO) and iron (Fe)-doped CuO thin films were successfully prepared at a temperature of 350 °C using a facile spray pyrolysis technique. Fe concentrations ranging from 2 to 8 at. % were varied in CuO to examine the impact of Fe-doping on the structural, morphological, optical, electrical, and electronic properties of the thin films. X-ray diffraction analysis confirmed a monoclinic crystal structure with prominent orientation along the (1¯11) plane. Fe-doping led to reduced crystallite sizes (45–27 nm) and increased microstrain and dislocation density. Scanning electron microscopy revealed a transformation from densely packed rock-like nanostructures to agglomerated nanoparticles incorporating Fe. The grain size decreased, averaging 0.556–0.330 μm. Energy-dispersive x-ray analysis confirmed the elemental composition and a proportional increase in Fe content. Optical transmittance reached ∼73% in the visible-NIR range, while the bandgap showed a tunable shift, rising from 1.28 to 1.56 eV at 4 at. % Fe, and then declining to 1.40 eV with further doping. Electrical resistivity decreased significantly from 1.69 to 0.24 Ω-cm. The films exhibited p-type conductivity as the carrier concentration increases from 1.11 × 1017 to 6.77 × 1017 cm−3. The Hall coefficient and mobility decreased with Fe-doping in CuO thin films. Density functional theory results showed that Fe doping introduced Fe-3d states near the band edges, modified the bandgap, and influenced electronic transport while preserving the monoclinic structure. These experimental and theoretical findings demonstrate that Fe doping can be an effective strategy for tailoring the physical properties of CuO thin films for optoelectronic and sensing applications.

The coupling of light detection, emission, and transmission, along with self-powering in a single optoelectronic chip, is required for next-generation, energy-efficient devices, yet remains severely challenging. Here, Zn-doped VO₂ (ZnVO₂) nanowire networks are grown on Cd-doped Ga₂O₃ (CdGa₂O₃) thin films to fabricate a transparent self-powered ZnVO₂/CdGa₂O₃ heterostructure, which simultaneously enables ultraviolet (UV) photodetection and luminescence down-conversion under a single excitation source. Individually, Cd doping in Ga₂O₃ destabilizes the characteristic self-trapped hole-associated UV emission and produces a broad green luminescence band resulting from Cd-induced defect state, while Zn-doping introduces oxygen vacancies, stimulating the green luminescence in ZnVO₂ along with the characteristic UV and yellow emissions originating from distinct recombination channels within its correlated electronic configuration. The heterostructure fabricated from ZnVO₂ nanowire and CdGa₂O₃ film exhibits semiconductor diode-like rectifying characteristics and functions as a self-powered ultraviolet photodetector with a high sensitivity of 251 mA/W and a fast response time of 85 ms. The built-in field at the heterostructure interface promotes effective charge-carrier segregation and recombination under zero bias, producing bright orange-red luminescence visible to the naked eye when the device functions as a self-powered UV photodetector. In particular, this integrated device maintains ~75% transparency and provides a clear view through the device architecture. This photodetector heterostructure absorbs 5-3 eV high-energy broadband UV light and converts it into low-energy orange-red luminescence covering 2.2-1.51 eV, reflecting efficient luminescent down-conversion. The coupling of broadband UV detection, visible-light emission, optical transparency, and self-powered operation into ZnVO₂/CdGa₂O₃ heterostructure makes it suitable for integrated photonics, photovoltaic windows, flexible display technologies, and luminescent down-conversion electrodes for photovoltaics.

Electrochemical water splitting requires low-cost electrodes to overcome sluggish oxygen evolution reaction (OER) kinetics in alkaline media. Here, zinc–aluminum (Zn–Al) alloy electrodes with up to 20 wt.% Al are developed via powder metallurgy and studied using electrochemical measurements and first-principles calculations. Alloys with ≥20 wt.% Al exhibit thermodynamic instability and phase segregation, limiting catalytic activity. In contrast, Zn₀.₉Al₀.₁ and Zn₀.₈₅Al₀.₁₅ show significantly enhanced performance, delivering ~3× and ~2× higher exchange current density than pure Zn. Zn₀.₉Al₀.₁ achieves a low overpotential of 0.24 V at 12 mA cm⁻², compared to 1.086 V for pure Zn, along with reduced charge-transfer resistance (~1.85 Ω·cm²). Lower Al content (5 wt.%) shows limited activity due to insufficient active sites. The improved performance is attributed to optimized electronic structure and enhanced charge-transfer kinetics. The optimized Zn–Al alloys demonstrate competitive activity with transition-metal-based catalysts, highlighting their potential as low-cost OER electrodes.