Doping and stacking effects for decaphenylcyclopentasilane (DPPS) hole transport layers in perovskite photovoltaic devices were investigated. Tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III) tri[bis(trifluoromethane)sulfonimide] (FK209) was added to DPPS as dopant, and the conversion efficiency of the DPPS stacked devices doped with FK209 increased over 12% after 43 days, which is almost same as that of spiro-OMeTAD, a conventional hole transport material. A three-layered perovskite/DPPS stacking structure also improved the conversion efficiencies of the devices. The first-principles calculation indicated the hole transport mechanism of DPPS. The calculated adsorption energy of DPPS with cations in the perovskite was found to be high, which would contribute to suppressing the desorption of CH3NH3. The present results indicated that equivalent efficiencies can be obtained using only chemically stable materials such as DPPS and FK209, without using unstable materials such as spiro-OMeTAD and Li-TFSI.

Silver nanoparticle (AgNP) aqueous solutions are expected to be applied to various functional materials, such as highly sensitive molecule detection using surface-enhanced Raman scattering (SERS). However, the shape and size control of AgNPs for practical applications is challenging without any additional stabilizers in the chemical synthesis process. In this study, a stepwise centrifugal classification method was evaluated for its applicability to polydisperse particles from a mathematical model and employed to classify AgNPs that were reduced and stabilized using trisodium citrate. The AgNPs could be separated, and aqueous solutions with different particle size distributions could be obtained by varying the centrifugation time and speed. Centrifugation with several steps could effectively improve the uniformity of AgNPs, while the loss of AgNPs was prevented by redispersing the precipitate in a solution of the citrate ion as a stabilizer. Furthermore, since this shape-control method is performed without any additional stabilizers, the obtained silver nanoparticles are applicable to Raman scattering measurements, thereby contributing to an enhanced spectral resolution.

Lanthanide (Ce, Er, Nd, Yb, Gd)-doped perovskite solar cells were fabricated and characterized. In Er-, Nd-, Yb-, and Gd-doped systems, an increase in the parallel resistance was observed in conjunction with improvements in the short-circuit current density, conversion efficiency, and external quantum efficiency. Notably, the Gd-doped system achieved the highest conversion efficiency. The conversion efficiency increased over a 126-day period. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed the formation of a dense perovskite layer in the Gd- and Er-doped systems. Doping reduced the trap density within the perovskite layer and improved the (100) orientation. First-principles calculations of the electronic structure predicted an increased bandgap for the Gd-doped system. Analysis of the photovoltaic characteristics utilizing a solar-cell simulator, which incorporates interface defect concentrations, confirmed the passivation effect induced by Gd incorporation.

Perovskite solar cells were fabricated and characterized using phthalocyanine and naphthalocyanine. These materials offer great advantages for application in photovoltaic devices in light of their electronic and optical properties, and heat and chemical resistance. Performance enhancement and long-term stability are possible through control of the center atom and substituents in phthalocyanine and naphthalocyanine. This research is focused on characterization of a perovskite solar cell using naphthalocyanines with chemical substituents on the axial ligand. The photovoltaic characteristics, optical properties, morphologies, crystallinity, and trap density were measured. In the system utilizing lead naphthalocyanine with chlorine substituents on the axial ligand, the open-circuit voltage and conversion efficiency were improved. Introduction of germanium and silicon naphthalocyanines bearing hydroxyl groups passivated the perovskite layer, improving the charge transfer and carrier diffusion. The crystal grain growth and orientation in the perovskite layer were confirmed through morphological observation using optical microscopy, scanning electronic microscopy, and energy-dispersive x-ray spectroscopy, as well as structural analysis via x-ray diffraction. The naphthalocyanines exhibited absorption in the ultraviolet–visible–near-infrared region, and showed a bandgap in the range of 1.08 eV to 1.45 eV. The photovoltaic mechanisms were evaluated through experimental results and energy level diagrams of the perovskite solar cell. Optimization of the energy levels in the highest occupied molecular orbital and lowest unoccupied molecular orbital and the bandgap of the naphthalocyanines support charge transfer and carrier diffusion while suppressing recombination near the interface of the perovskite crystal and hole transport layer.

Addition of rare earth elements to CH3NH3PbI3 perovskite solar cells has been investigated for improving conversion efficiency and stability. The perovskite solar cells co-doped with ytterbium (Yb) and neodymium (Nd) were fabricated and characterized. Co-doped with 0.5 at% Yb and Nd to the perovskite solar cells affected in conversion efficiency and stability. The orientation and crystallite size were increased with co-doping of Yb and Nd. Optimization of internal structure based on crystal growth in the co-doped layer supported to improve the photovoltaic characteristics such as the open-circuit voltage and short circuit current density, conversion efficiency and stability. The surface morphology and elemental mapping demonstrated that the perovskite grains containing rare earth element were uniformly and finely distributed, forming the dense film in the active layer. The photovoltaic mechanism were discussed by experiments and energy level diagram of the perovskite solar cell. Addition of Yb and Nd ions as passivating effect promoted the crystal growth and orientation. The electron density distributions at 4f and 5d orbitals of Yb and Nd ions were narrowly distributed, promoting charge transfer and transport characteristics. The band gap was calculated from dielectric function, absorption coefficient and Tauc-plot. The optical properties originate from the band structure accompanying 4f and 5d orbitals of Yb and Nd ions. Molecular dynamics calculations predicted the crystal stability and structural distortion. The Yb and Nd-doped system had more stabilization than the Pb-defective system. The performance depends on defects and internal structure in the system.

Electronic structure, dielectric function, and optical properties of Cs2MM'Cl6 (M = Ag, Na, Cu; M' = Sc, Ti, V, Cr, Mn, Fe, Co, Ni) double perovskite crystals were analyzed for improving the photovoltaic performance of lead-free double perovskite solar cell. In the case of Cs2MM'Cl6 (M = Ag, Na, Cu), tolerance factor and formation enthalpy were decreased with lattice constant, expecting crystal stability. In the case of Cs2AgM'Cl6 (M' = Cr, Fe), real and imaginary parts in dielectric function are based on spin polarization, expecting the optical properties in visible absorption region. Band structure and partial density of state demonstrated that the 3d orbitals of Cr3+ and Fe3+ ions and 3p orbital of Cl− ion were distributed near conduction and valence bands. Effective mass ratio near the conduction bands and band gap were obtained to be 0.58 and 2.23 eV. Device simulations expected that the Cs2AgFeCl6 crystal was a suitable material for use in the photovoltaic devices as compared to the conventional Cs2AgBiBr6 double perovskites solar cell.

The additive effect of Ni or V on formamidinium (FA)-based Sn-Pb mixed perovskite crystals on the electronic structure was investigated. The objective of this study was to propose a more appropriate substituent than V in FASn0.5Pb0.375M0.125I3 (M = Ni or V) regarding the electronic structure and to demonstrate the potential for Ni introduction via first-principles calculations. Charge-density distribution and partial density of states indicated that the V and Ni 3d orbitals were split. Band structure analysis revealed that FASn0.625Pb0.375I3 had an electron effective mass ratio (me*/m0) of 0.186. For FASn0.5Pb0.375V0.125I3, the conduction-band minimum (CBM) was characterized by the appearance of V 3d orbitals, leading to an increase in me*/m0 to 0.646. Conversely, for FASn0.5Pb0.375Ni0.125I3, the CBM was dominated by Ni 4s orbitals, resulting in a reduced me*/m0 of 0.169 under the direct-transition process. Moreover, the direct bandgap increased from 0.87 eV for FASn0.625Pb0.375I3 to 1.25 eV for FASn0.5Pb0.375V0.125I3 and 1.27 eV for FASn0.5Pb0.375Ni0.125I3. FASn0.5Pb0.375Ni0.125I3 exhibited overlapping Sn 5p and I 5p and Ni 4s orbitals, and the carrier path was expected to be extended by Ni 4s. A possible increase in mobility was suggested, contributing to the decrease in me*/m0. Ni up-and down-spin had different excitation processes, which was expected to extend the absorption wavelength. Molecular dynamics calculations demonstrated that the stability of the Ni-substituted crystal was superior to that of the V-substituted crystal.

Electronic structures, optical and thermal properties of lanthanide-based lead-free perovskite crystals have been characterized for applications of electron devices with broadband emission in near-infrared region. The purpose of the study is to characterize electronic structure, real and imaginary of dielectric function, absorption coefficient, acoustic phonon, molecular dynamics, electronic and thermal conductivity of cesium ytterbium chloride (CsYbCl3) perovskite crystal for improving the semi-conductive properties enhanced with optical properties over the ultraviolet-visible-near-infrared region. The CsYbCl3 crystal have direct narrow band gap between valence band state of occupied 4f orbital of Yb2+ ion and conduction band state of widely split 5d orbital of Yb2+ ion, corresponding to absorption in the near-infrared region. The acoustic phonon as the lattice vibrations with imaginary mode exhibited dynamic instability due to the tilt of the octahedral structure. The hole-conductively on the tetragonal crystal can be explained by inhabitation of the carrier diffusion with acoustic phonon based on the lattice vibration in the high temperature region. The CsYbCl3 crystal at cubic rather than tetragonal state have high potential to apply the photovoltaic device with the optical properties in the near-infrared region.

Decaphenylcyclopentasilane (DPPS) was applied as a hole transport layer for CH3NH3PbI3 solar cells, and the photovoltaic properties were investigated. The insertion of the double DPPS layers between the perovskite crystal and the gold electrodes increased short-circuit current densities and open-circuit voltages, and the conversion efficiencies were improved. The external quantum efficiencies increased in the visible light region, and the maximum power point tracking tests under air mass 1.5 light irradiation indicated the effectiveness of the DPPS layer. Microstructural analysis showed that no PbI2 compound was formed for the DPPS-inserted perovskite, which indicates the suppression of methylammonium desorption from the perovskite crystal. The double DPPS-induced devices were also stable in air for more than 1 year, which indicates that stable DPPS can reliably transport holes and has great potential for the future solar cell materials.

A series of organic thin-film solar cells using electrodeposited polythiophene films were fabricated and characterized. The cells consisted of an indium-tin oxide transparent electrode/electrodeposited poly(3,4-ethylenedioxythiophene) doped with different anions as a hole transport layer/electrodeposited poly(2,2 '-bithiophene) film as a photoexciting p-type semiconductor layer/[6,6]-phenyl-C61-butyric acid methyl ester as an n-type semiconductor layer/aluminum as a top electrode, were fabricated. Obtained solar cells were characterized and photoelectric properties were evaluated. These organic thin-film solar cells generated photovoltages and photocurrents. The photovoltaic property was varied depending on the structure of dopant anions, which seems to be correlated with the surface morphology of each poly(3,4-ethylenedioxythiophene)-dopant anion. S S n Electrodeposited polyBiTh O O S n SO3-Na+ Electrodeposited polyEDOT C12H25 SO3-Na+ SS DBS Al PCBM polyBiTh polyEDOT (SS, Na2SO4, DBS) ITO hv PCBM (CH2)3COOMe (c) The Author(s) 2025. Published by ECSJ. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium provided the original work is properly cited. [DOI: 10.5796/electrochemistry.25-00051].

Copper oxide (CuO) and magnesium (Mg)-doped CuO thin films were fabricated by spin coating, and then their properties were characterized. In the Mg-doped CuO thin films, a minor phase of MgCu2O3 was observed in addition to CuO. Optical absorption analysis revealed that Mg doping narrows the energy gap of CuO. Devices containing Mg-doped CuO thin films exhibited photovoltaic characteristics under illumination. These devices demonstrated the effectiveness of spin coating as a simple and inexpensive method for fabricating photoconversion layers. This study advances the development of CuO-based solar cells fabricated using spin coating.

The effects of potassium (K) or germanium (Ge)-addition to methylammonium-formamidinium-based perovskite crystals were investigated on the device performance and electronic structures. The Ge-addition increased the short-circuit current density for the as-prepared device, and the K-addition improved the open-circuit voltage and conversion efficiency by room temperature aging. Crystallite sizes and (100)-orientations of perovskite crystals increased by the K-addition, and the lattice constants of K- and/or Ge-doped perovskites increased with time. The first-principles calculations indicated that the formation energies of the perovskite crystals were reduced by the K- or Ge-addition, which would contribute to the stability of the perovskite crystals.

The photodurability of unencapsulated methylammonium-based perovskite solar cells prepared with different device configurations using different precursor solution compositions was investigated. Devices with a decaphenylcyclopentasilane layer on the perovskite layer exhibited higher durability against light irradiation. The photovoltaic performance of the light-irradiated devices recovered to levels close to those before the maximum power point tracking measurements after 1 week of storage in a darkroom. Lattice expansion due to light irradiation and contraction upon storage in the dark were observed, possibly due to the displacement of the atoms and molecules. First-principles calculations on the dimethylammonium-added perovskites indicated that the activation energy for atomic diffusion was reduced, suggesting that the atoms could diffuse more rapidly as the lattice expanded under light irradiation. The photovoltaic performance improved owing to the slow migration of atoms and molecules to their original atomic sites during room-temperature aging in the dark. This study contributes to the elucidation of the recovery mechanisms of the photovoltaic properties of perovskite solar cells, which are expected as next-generation energy devices.

Densely-packed thin films of plasmonic nanoparticles enhance Raman scattering. The effect of size uniformity of plasmonic nanoparticles in such thin films contributes to the development of highly sensitive Raman scattering spectroscopy for practical use. In this research, densely-packed thin films containing a mixture of gold nanoparticles with two different sizes are fabricated and evaluated about their surface-enhanced Raman scattering properties. The enhancement efficiency of gold nanoparticle films with different sizes is lower than that of single-sized gold nanoparticle films. This tendency suggests a relationship between Raman scattering enhancement efficiency and the electric field generated by localized surface plasmon resonance among gold nanoparticles of different sizes.

Germanium (Ge) was added to formamidinium cesium lead triiodide perovskite crystals and the microstructures and photovoltaic properties were investigated. The Ge addition stabilized the α-phase of the perovskites and suppressed formation of the δ-phase. X-ray diffraction peaks of the α-phase increased by increasing the Ge contents. The highest conversion efficiency of 6.05% was obtained for the 12.5% Ge added device in an air atmosphere and the increase of efficiencies would be due to the promoted formation of photoactive α-formamidinium cesium lead triiodide perovskite crystals.

Double-stacked formamidinium-based perovskite photovoltaic devices with different bandgaps were fabricated using decaphenylcyclopentasilane (DPPS) as the hole-transport layer, and their photovoltaic properties were evaluated. Perovskite/DPPS hybridized thin films were fabricated under a high temperature of 190 °C. The DPPS layer functioned as a protective layer and the efficiencies of the DPPS-based devices were maintained even after one year. Optical and microstructural analyses were performed to investigate the microstructure and properties of the DPPS, and its crystallization was observed after annealing. The crystal growth of the perovskite layer was enhanced in the thicker region of the crystallized DPPS film, which suggests that the suppression of CH3NH3 desorption by DPPS improved the quality of the perovskite films.

The effects of adding dimethylammonium (DMA) to CH3NH3PbI3 perovskite solar cells were investigated using device fabrication and first-principles calculations. For the methylammonium (MA) system, the appropriate amount of DMA to add at the MA site was found to be 30-35 %. The addition particularly contributed to the improvement of the fill factor, which enhanced the power conversion efficiencies. This was due to improved interfacial conditions, such as reduced grain boundaries resulting from increases in the crystallite size and (100) orientation. In addition, DMA and guanidinium (GA) were both added to CH3NH3PbI3 perovskite solar cells, which improved the photovoltaic properties and long-term stability. This could have been due to the stabilization of the crystal structures by the co-addition of DMA/GA, which have larger ionic radii than MA. First-principles calculations suggested an increase in carrier mobility by the DMA introduction and stabilization of the crystal lattices by the co-addition of DMA/GA, which supported the effectiveness of the DMA addition.

A monovalent copper ion (Cu+) with the same valence as formamidinium is focused on the present work, and the effects of A-site inorganic cations on the electronic structures and device performance are discussed from the experiments and the first-principles calculations. The addition of inorganic cations increased the conversion efficiencies, and the copper-doped device showed the highest conversion efficiency. In particular, the hysteresis of current density-voltage characteristics was significantly suppressed by the addition of Cu+, which would be due to suppression of iodine ion (I-) diffusion by electrostatic interaction between Cu+ and I-. The addition of rubidium or cesium contributed to the increase in short-circuit current density by suppressing decomposition of perovskite crystals and formation of PbI2.