In this work, we report on solution-based p-i-n-type planar-structured CH₃NH₃PbI₃perovskite photovoltaic (PV) cells, in which precrystallized NiO nanoparticles (NPs) without post-treatment are used to form a hole transport layer (HTL). X-ray diffraction and high-resolution transmission electron microscopy showed the crystallinity of the NPs, and atomic force microscopy and scanning electron microscopy confirmed the uniform surfaces of the resultant NiO thin film and the subsequent perovskite photoactive layer. Compared to the conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL, the NiO HTL had excellent energy-level alignment with that of CH₃NH₃PbI₃and improved electron-blocking capability, as analyzed by photoelectron spectroscopy and diode modeling, resulting inV_oc~0.13 V higher than conventional PEDOT:PSS-based devices. Consequently, a power conversion efficiency (PCE) of 15.4% with a high fill factor (FF, 0.74), short-circuit current density (J_sc, 20.2 mA·cm⁻²), and open circuit voltage (V_oc, 1.04 V) having negligible hysteresis and superior air stability has been achieved.

We investigated operation of a planar MAPbI₃ solar cell with respect to intensity variation ranging from 0.01 to 1 sun. Measured J-V curves consisted of space-charge-limited currents (SCLC) in a drift-dominant range and diode-like currents in a diffusion-dominant range. The variation of power-law exponent of SCLC showed that charge trapping by defects diminished as intensity increased, and that drift currents became eventually almost ohmic. Diode-like currents were analysed using a modified Shockley-equation model, the validity of which was confirmed by comparing measured and estimated open-circuit voltages. Intensity dependence of ideality factor led us to the conclusion that there were two other types of defects that contributed mostly as recombination centers. At low intensities, monomolecular recombination occurred due to one of these defects in addition to bimolecular recombination to result in the ideality factor of ~1.7. However, at high intensities, another type of defect not only took over monomolecular recombination, but also dominated bimolecular recombination to result in the ideality factor of ~2.0. These ideality-factor values were consistent with those representing the intensity dependence of loss-current ratio estimated by using a constant internal-quantum-efficiency approximation. The presence of multiple types of defects was corroborated by findings from equivalent-circuit analysis of impedance spectra.

Carbon quantum dots (CQDs) have garnered considerable interest due to their distinctive optical properties, cost-effectiveness, and eco-friendly synthesis routes. This study investigates CQDs synthesized from orange peels through a sustainable hydrothermal method. The CQDs were characterized using UV-Vis spectroscopy, fluorescence spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM) to elucidate their optical and structural properties. Multi-Gaussian fitting of the photoluminescence (PL) spectra was employed to deconvolute the emission profiles, revealing the contributions of the zero-phonon line (ZPL) and phonon sidebands, which correlate closely with the characteristic carbonyl (C=O) stretching mode at approximately 0.21 eV, as identified by FT-IR. The Huang-Rhys factor, calculated from both the PL spectral analysis and the Stokes shift, quantifies the electron-phonon coupling strength, providing insights into the recombination dynamics. The synthesized CQDs exhibited robust blue fluorescence under UV excitation, with excitation-wavelength-dependent tunable emission. Moreover, the CQDs achieved a significantly enhanced quantum yield compared with previously reported orange peel–derived counterparts, together with stable radiative lifetimes, demonstrating efficient radiative recombination. These features confirm their strong potential for bioimaging, optoelectronic, and sensing applications and reinforce the viability of fruit waste as a sustainable precursor for high-quality fluorescent nanomaterials with well-defined vibronic characteristics.

Sustainable rice straw-derived N,S-co-doped carbon quantum dots enable highly selective and sensitive fluorescent detection of Hg ²⁺ in water.