Abstract This review examines the sidewall damage effects in GaN-based micro- and nano-light emitting diodes ( μ LEDs/nLEDs) fabricated via top–down inductively coupled plasma reactive ion etching. We analyze the structural and electronic properties of etched surfaces, damage mitigation strategies through process optimization, and postetch treatments. Furthermore, we evaluate models explaining performance degradation with a decrease in device dimensions. Blue InGaN/GaN μ LEDs exhibit severe efficiency degradation below ∼20 μ m diameter (the ‘efficiency cliff’), whereas green and red devices show greater resilience. We attribute this behavior to differences in surface recombination velocity, carrier diffusion length, and localization effects. Surface treatments including tetramethylammonium hydroxide etching, (NH 4 ) 2 S passivation, hydrogen plasma treatment, and atomic layer–deposited dielectrics significantly mitigate damage. Deep-level transient spectroscopy reveals nitrogen interstitial (N i ) acceptors near E C -1 eV and gallium vacancy (V Ga ) complexes near E V + 0.8 eV as the dominant recombination centers. The damaged region extends 0.5–1 μ m from sidewalls—significantly beyond the structurally damaged zone (∼40–100 nm). Emerging approaches, such as neutral beam etching and localized surface plasmon coupling, show promise for achieving high efficiency in sub-5 μ m devices required for advanced display applications.

Thermal performance of perovskite solar cells (PSCs) under elevated operating temperatures is one of the key-bottlenecks for commercial deployment. While composition engineering has driven competitive power conversion efficiencies (PCEs), its impact on defect landscape is rarely quantified at the device level under harsh thermal stress (85°C). Here we compare two CsxFA1-xPbI3 absorbers (x = 0.05 and 0.20) through structural, optical, and ionic transport measurements under prolonged ISOS-D-2 testing. Devices with reduced Cs concentration achieved a PCE of 22.23% with superior room-temperature recombination metrics, attributed to reduced lattice strain (ε = -0.00431) and longer charge carrier lifetimes. However, temperature-coefficient measurements reveal that this advantage reverses under heating, with TPCE reaching -0.624%/°C versus -0.294%/°C for Cs 20%, driven predominantly by fill factor losses. Aging-resolved admittance and photo-induced spectroscopies show activation energy rising from 0.4 eV (Cs 5%) to >0.6 eV (Cs 20%), with ionic diffusion coefficients tracking JV hysteresis amplitude during thermal stress. In Cs 20% devices, CsPbI3-rich cluster formation acts as an ionic sink, passivating active interfaces, whereas in Cs 5% devices unimpeded ion migration along grain boundaries with PbI2 formation affects charge collection. These findings show room-temperature efficiency and thermal ionic stability aren’t directly decoupled parameters requiring independent compositional optimization.

Despite competitive efficiency compared to Si solar cells and relevant stability at near room temperatures, the rapid degradation at elevated temperatures remains the critical obstacle for the exploitation of perovskite photovoltaics. In this work, a 4-(pyridin-4-yl)triphenylamine (TPA-Py) with pyridine anchor group was employed for intergrain bulk modification of double-cation CsCH(NH2)2PbI3 perovskite absorbers to enhance thermal stability. Through coordination and dipole-dipole interactions, nitrogen-containing fragments (diphenylamine and pyridine) of TPA-Py passivate uncoordinated cations and improve the phase resilience of perovskite films against segregation. This resulted in a power conversion efficiency of 21.3% with a high open-circuit voltage of 1.14 V. Notable impact of self-assembled monolayer incorporated into the bulk of the perovskite film manifested in a huge improvement of thermal stability at 85 degrees C (ISOS-D-2). TPA-Py modification extended the T80 lifetime to approximate to 700 h compared to only 200 h for the reference under harsh heating stress in ambient conditions. In-depth analysis using photoinduced voltage transients and admittance spectroscopy after different stress periods revealed the screening of ion migration (0.45 eV) for devices with TPA-Py. This work offers an important understanding of the bulk modification of microcrystalline perovskite absorbers and a guide for robust design of bulk and buried interfaces in highly efficient perovskite solar cells.

The synthesis and exploration of the properties of activated porous carbons - materials capable of capture of substances - increasingly attracts the attention of researchers nowadays. However, studies generally focus on absolute values of adsorption (or other) properties. Pretreatment of carbonaceous materials, whether at high or low temperatures, plays a key role in generating the precursor structure that is subsequently activated. Our research addresses a gap in the existing literature by exploring how pretreatment conditions influence the properties of activated carbon. For the first time, we show how both the pretreatment atmosphere (inert or air) and the temperature used affect the final structure and adsorption performance of polyacrylonitrile-based activated carbons. We found that as the pretreatment temperature increases, the specific surface area decreases, and the crystallite size grows. The sample without any pretreatment showed the largest surface area of 2298.3 m2/g and the best adsorption capacity for methylene blue, reaching 508.4 mg/g. However, it also possesses the lowest nitrogen content, affecting its suitability for certain applications. Additionally, pretreatment atmosphere influences surface characteristics, with inert pretreatment resulting in higher hydroxyl group concentration compared to air pretreatment. This difference in hydroxyl groups contributed to varied adsorption values, measuring 441.2 and 422.6 mg/g for the inert and air pretreated samples, respectively. This highlights the importance of both pretreatment temperature and atmosphere in tailoring the properties of activated carbons for diverse applications.

Owing high conductivity in microcrystalline thin-films, CsSnI3 perovskite is a promising semiconductor for thermoelectrics and optoelectronics. Rapid oxidation of thin-film and intrinsic lattice strain hinders stabilization of the device performance. Cation engineering of perovskite molecule was considered as an effective strategy to tailor the structural properties and suppress the degradation processes. However, molecular engineering demands a thorough analysis of defect behavior, as it can influence ionic motion, recombination dynamics, and capacitive effects. The effective implementation of CsSnI3 in energy conversion devices requires careful consideration of the specific properties of thin films electrical conductivity, Seebeck coefficient, power factor, as well as electronic transients, and charge transport in the device structures. In this work, we performed a complex investigation for modified CsSnI3 through cation substitution with methyl ammonium (MA) and formamidinium (FA). Our findings highlight a complex interplay between electrical parameters of the bare thin films and stability of the devices (p-i-n diodes) after thermal stress. FA-CsSnI3 showed beneficial results for stabilization under elevated temperatures with improved non-ideality factor in diode structures, enhanced shunt properties and reduced trapping. The photo-induced voltage relaxation spectroscopy performed for MA-CsSnI3 showed relevant traps concentration of 1016 cm-3 with activation energy of 0.52 eV(210K) likely attributed to Sn atom defect. The obtained results are deeply analyzed and discussed.

Current-voltage characteristics in the dark and under illumination, capacitance-voltage characteristics and admittance spectra in the dark and under illumination were measured for two sets of p-SnO2:Mg/i-ZrxSn1-xO2/n-SnO2/n+SnO2:Nb structures. These data strongly point to the structures demonstrating clear-cut persistent photocapacitance behavior existing for temperatures above room temperature. The phenomenon is shown to be due to the centers in the i-ZrxSn1-xO2 layer. These centers are believed to be related to residual Nb donors coming from Nb doped SnO2 layers. The analogy is drawn between the above-mentioned effect and the persistent photocapacitance phenomena in n-type doped AlGaN films for varying Al compositions that have been convincingly explained in the literature as in fact due to some of the standard n-type dopants being DX-like centers with a high barrier for capture of electrons. For the two studied p-SnO2/i-ZrxSn1-xO2/n--SnO2/n+-SnO2:Nb samples the thermal ionization energy, the barrier for capture of electrons, the optical ionization energy of the centers responsible for persistent photocapacitance have been estimated. The results suggest that the photoresponsivity of the samples increases when increasing the Zr mole fraction closer to the value of x = 0.3 and the concentration of centers responsible for persistent behavior decreasing from some 1017 cm-3 to some 1016 cm-3.

Traps and structural defects at the hole and electron transport interfaces of the microcrystalline absorber limits the efficiency and long-term stability of perovskite solar cells (PSCs) due to accumulation of the ionic clusters, non-radiative recombination and electrochemical corrosion. Surface engineering using self-assembled mono- layers (SAM) was considered as an effective strategy for modification of charge-collection junctions. In this work, we demonstrate the first report about complex integration of a SAM for double-side passivation in p-i-n PSCs. Integrating the novel 5-(4-[bis(4-fluorophenyl)amino]phenyl)thiophene-2-carboxylic acid (FTPATC) as a fluorinated SAM at the hole-transport interface reduced potential barriers and lattice stresses in the absorber. At the electron-transport side, FTPATC interacted with the A-site cations of the perovskite molecule (Cs, formamidinium), inducing a dipole for defect compensation. Using the passivation approach with fluorinated SAM demonstrated benefits in the gain of the output performance up to 22.2 %. The key-advantage of double-side passivation was confirmed by the enhanced stability under continuous light-soaking (1-sun equivalent, 65 degrees C, ISOS-L-2), maintaining 88 % of the initial performance over 1680 h and thermal stabilization under harsh heating at 90 degrees C.

The catalytic properties of samples containing Pd and Co metals on carbon supports (IR-pyrolyzed chitosan (CT) with an activated surface and detonation nanodiamonds (DNDs) have been studied in the ethanol steam reforming process. CT is a promising catalyst support due to its developed surface and the presence of nitrogen-containing groups capable of sorbing water molecules. The use of a membrane reactor with a Pd–Ru–In membrane has significantly increased the efficiency of the ethanol steam reforming process due to removing hydrogen from the reaction zone. The hydrogen yield in the membrane reactor increases twofold or more compared to a conventional reactor, while the proportion of reaction byproducts (CO and acetaldehyde) decreases. The highest hydrogen yield (15.8 mol/h per gram of catalyst) in the membrane reactor is achieved using a Pd–Co/CTKOH catalyst.

Deep trap spectra and carrier diffusion lengths were measured for unintentionally doped β-Ga2O3 bulk crystals with (100) orientation. The 20-mm diameter, 15-mm length boule was pulled by the Czochralski method from gallium oxide in (010) direction. It is found that the net density of shallow donors in (100) plates cleaved from the crystal was 2.6 × 1017 cm−3, with ionization energies of 0.05 eV measured from admittance spectra. Three deep electron traps with respective ionization energies of 0.6 eV (concentration 1.1 × 1014 cm−3), 0.8 eV (concentration 3.9 × 1016 cm−3) and 1.1 eV (concentration 8.9 × 1015 cm−3) were detected by Deep Level Transient Spectroscopy. The dominant 0.8 eV trap is associated with the E2 centers due to Fe acceptors, the two other traps are the well documented E1 and E3 centers. The major deep acceptors in the lower half of the bandgap have optical ionization threshold of 2.3 eV and concentration of 4 × 1015 cm−3 and are believed to be due to the split Ga vacancies acceptors. The diffusion length of non-equilibrium charge carriers was 90 nm. The electrical properties of these (100) oriented crystals grown by Czochralski are quite similar to those synthesized by the undoped Edge-defined Film-Fed Growth technique.

We report the electrical properties, deep trap spectra, and diffusion lengths of non-equilibrium carriers in Ni Schottky diodes and NiO/Ga2O3 heterojunctions (HJs) prepared on the same n(-)/n(+) beta-Ga2O3 epi structures. The heterojunctions decrease the reverse current of Ga2O3 high-power rectifiers. In HJs, in contrast to Schottky diodes, the capacitance and AC conductance show a prominent frequency and temperature dependence, suggesting the presence of two temperature activation processes with activation energies of 0.17 and 0.1 eV. The deep trap spectra of the Schottky diodes and HJs differ by the absence in the HJ of deep electron traps E2* with level near E-c - 0.7 eV considered to be an important center of non-radiative recombination. This correlates with the observed increase in the diffusion length of non-equilibrium charge carriers in the HJs to 370 nm compared to 240 nm in the Schottky diodes. The diffusion length of charge carriers in p-NiO was found to be quite short, 30 nm. Possible reasons for the observed differences and possible origin of the minority-trap-like feature commonly reported to be present in the deep level spectra of HJs and also observed in our experiments are discussed.

Heterojunctions (HJs) of p-NiO/n-Ga2O3 were prepared by deposition of thin films of p-NiO by ion beam sputtering on bulk nominally undoped (100) oriented n-Ga2O3 samples cleaved from Czochralski-grown (010) oriented crystal. Electrical properties and deep traps spectra were studied and compared with those obtained for similar samples with Ni Schottky diodes. Characteristic features of the NiO/Ga2O3 HJs are the built-in voltage of over 2 V compared to 1 V in Ni Schottky diodes, a strong frequency dispersion of capacitance due to the presence of high density over 10(18) cm(-3) of E-c-0.16 eV traps in the thin region adjacent to the NiO/Ga2O3 interface. For heterojunction diodes the strong increase of reverse current occurs at a much higher voltage than for Schottky diodes (120 V versus 60 V).

We report the electrical properties, deep trap spectra, and diffusion lengths of non-equilibrium carriers in Ni Schottky diodes and NiO/Ga2O3 heterojunctions (HJs) prepared on the same n−/n+ β-Ga2O3 epi structures. The heterojunctions decrease the reverse current of Ga2O3 high-power rectifiers. In HJs, in contrast to Schottky diodes, the capacitance and AC conductance show a prominent frequency and temperature dependence, suggesting the presence of two temperature activation processes with activation energies of 0.17 and 0.1 eV. The deep trap spectra of the Schottky diodes and HJs differ by the absence in the HJ of deep electron traps E2* with level near Ec − 0.7 eV considered to be an important center of non-radiative recombination. This correlates with the observed increase in the diffusion length of non-equilibrium charge carriers in the HJs to 370 nm compared to 240 nm in the Schottky diodes. The diffusion length of charge carriers in p-NiO was found to be quite short, 30 nm. Possible reasons for the observed differences and possible origin of the minority-trap-like feature commonly reported to be present in the deep level spectra of HJs and also observed in our experiments are discussed.

The stable beta polymorph Ga 2 O 3 was converted to gamma polymorph by ion irradiation. The current–voltage characteristics show the gamma polymorph is much more rad-hard.

Direct observation of the capture cross section is challenging due to the need for extremely short filling pulses in the two-gate Deep-Level Transient Spectroscopy (DLTS). Simple estimation of the cross section can be done from DLTS and admittance spectroscopy data but it is not feasible to distinguish temperature dependence of pre-exponential and exponential parts of the emission rate equation with sufficient precision conducting a single experiment. This paper presents experimental data of deep levels in β-Ga2O3 that has been gathered by our group since 2017. Based on the gathered data, we propose a derivation of apparent activation energy (Eam) and capture cross section (σnm) assuming the temperature dependent capture via the multiphonon emission model, which resulted in a strong correlation between Eam and σnm according to the Meyer–Neldel rule, which allowed us to estimate low- and high-temperature capture coefficients C0 and C1 as well as capture barrier Eb. It also has been shown that without considering the temperature dependence of capture cross section, the experimental values of σn are overestimated by 1–3 orders of magnitude. A careful consideration of the data also allows to be more certain identifying deep levels by their “fingerprints” (Ea and σn) considering two additional parameters (EMN and σ00) and to verify the density functional theory computation of deep-level recombination properties.

Interface engineering is one of the most critical directions in the development of photovoltaics (PVs) based on halide perovskites. A novel triphenylamine-based hole transport material (HTM) with a carboxyl anchoring group (TPATC) was developed for tuning the interface between nanocrystalline NiO and CsCH3(NH2)2PbI3-xClx absorber in p-i-n device architectures. Transient spectroscopy measurements revealed that modification of the NiO surface with TPATC in perovskite solar cells (PSCs) reduces the concentration of ionic defects by an order of magnitude and reconfigures the energy levels of traps. Interface engineering allowed to reach power conversion efficiency of 20.58% for small area devices (0.15 cm2) under standard AM 1.5 G conditions. Using TPATC interlayer also provided sustainability of the perovskite absorber to decomposition under operation conditions. After continuous light-soaking (ISOS-L-2 protocol), NiO/TPATC devices showed a slight decrease of 2% in maximum power. We explored the potential of TPATC to modify interfaces in perovskite solar modules (PSM, active area-64.8 cm2). By applying slot-die-coated TPATC, the PCE at AM 1.5 G conditions increased from 13.22% for NiO PSM to 15.64% for NiO/TPATC ones. This study provides new insights into the interface stabilization for perovskite solar cells, behavior of the ionic defects and their contribution to the long-term stability.

In this study, we present a complex investigation for miniaturizing of perovskite photodiodes (PPDs) in various geometries with use of ultraviolet laser scribing (UV-LS). Employing a 355 nm (3.5 eV) pulsed laser at 30 kHz, we successfully manufactured PPDs with pixel configurations of 70x130 um2, 520x580 um2, and 2000x2000 um2. The utilization of UV-LS has a proven efficiency in achieving relevant diode characteristics, such as low dark currents and high shunt resistance, as well as ultrafast response. The multi-step scribing cycle provided precise patterning of perovskite photodiodes (PPDs) in a string design. The dark current densities demonstrated exceptional uniformity, ranging from 10-10 A/cm2 for 2000x2000 um2 pixelated PPDs to 10-9 A/cm2 for the 70x130 um2 configuration. The string PPDs, consisting of 10 pixels per string, displayed homogenous dark current values, ensuring effective isolation between devices. Under green light illumination (540 nm), all PPD types exhibited a broad Linear Dynamic Range (LDR). Specifically, LDR values reached 110 dB, 117 dB, and 136 dB for 70x130, 520x580, and 2000x2000 devices, respectively, spanning an illumination intensity range from 2*10-3 mW/cm2 to 2 mW/cm2. High responsivity values up to 0.38 A/W, depending on the PPDs geometry, highlight the potential of laser scribing devices for sensing in the visible range. The calculated specific detectivity performance (from 1011 to 1013 Jones) surpasses commercial analogs, while the sub-microsecond response of 70x130 um2 and 520x580 um2 miniaturized devices underscores their suitability for precise time resolution detection systems.

Deep trap states were examined in c-plane, Al-polar AlN epilayers, deposited via metal organic chemical vapor deposition on 270 nm thick AlN buffer layers on sapphire substrates. Contacts were created using e-beam deposited Ni through a shadow mask, with I-V characteristics revealing a trapped limited current (TLC) regime and voltage-dependent hysteresis upon light-emitting diode illumination. Thermally stimulated current and photothermal ionization current spectroscopy measurements demonstrated a prominent trap activation energy of approximately 0.75 eV and additional trap energies of 0.6, 0.4, 0.25, 1.05, and 1.1 eV. The observed differences in photocurrent responses between forward and reverse biases suggest that forward bias induces electron trapping at deeper levels, influencing the TLC behavior. Comparisons with bulk n-type AlN crystals from previous studies show similarities in deep trap spectra, suggesting commonality in trap characteristics across different AlN samples.

Herein, we have explored the recombination dynamics and defect concentration of a mixed cation mixed halide perovskite Cs0.17FA0.83PbI1.8Br1.2 with 1.75 eV bandgap after exposure to a gamma-ray source (2.5 Gy/min). We used photoluminescent spectroscopy to observe changes in recombination dynamics on perovskite films, impedance spectroscopy to reveal the contribution of interface recombination, and admittance spectroscopy to define the activation energy and concentration of defects. It was revealed that moderate doses (up to 10 kGy) passivate defects with activation energy ≈ 0.5 eV and at the same time form new defects that cause dramatic growth of the diffusion coefficient and migration of mobile ions. These two processes with opposite direction result in high radiation tolerance of the studied material and solar cells up to 10 kGy. Doses above 10 kGy are detrimental for perovskite solar cells, mainly due to the growing role of interface recombination. The results encourage the use of the wide bandgap perovskite Cs0.17FA0.83PbI1.8Br1.2 as a material for tandem solar cells with potential applications in a space environment.

The strategy of incorporating self-assembled monolayers (SAMs) with anchoring groups is an effective and promising method for interface engineering in perovskite solar cells with metal oxide charge-transporting layers. However, coating SAM layers in upscaled perovskite solar modules (PSMs) using slot-die coating is challenging due to the low viscosity and wettability of the solutions. In this study, a triphenylamine-based polymer poly([{5-[4-(diphenylamino)phenyl]-2-thienyl}(4-fluorophenyl)methylene]malononitrile) (pTPA)-TDP, blended with SAM based on 5-[4-[4-(diphenylamino)phenyl]thiophene-2-carboxylic acid, is integrated to address these challenges. And, p-i-n-oriented PSMs on 50 x 50 mm2 substrates (12 sub-cells) are fabricated with a NiO hole-transport layer and organic interlayers for surface modification. Wetting angle mapping shows that ununiform regions of the slot-die-coated SAM has extreme hydrophobicity, causing absorber thickness fluctuations and macro-defects at buried interfaces. The blended interlayer at the NiO/perovskite junction homogenizes surface wettability and mitigates lattice strain, enabling the effective use of SAM properties on large surfaces. This improved energy level alignment, enhancing the power conversion efficiency of the modules from 13.98% to 15.83% and stability (ISOS-L-2, T80 period) from 500 to 1630 h. In these results, the complex effects of using SAM in slot-die-coating technology for large-scale perovskite photovoltaics are highlighted. In this study, the challenges of integrating self-assembled monolayers (SAMs) into large-scale perovskite solar modules (PSMs) using slot-die coating are explored. Herein, a novel approach is presented combining a triphenylamine-based polymer with SAMs to mitigate the wetting issues for SAM interlayers for layer-by-layer slot-die coating of p-i-n PSMs. In this method, the morphology of the buried interfaces and the current-voltage performance in general are improved.image (c) 2024 WILEY-VCH GmbH

Arrays of nanorod multi-quantum-well (MQW) blue light emitting diodes (nLEDs) with diameter 800nm were prepared by reactive ion etching (RIE) with subsequent surface treatment by KOH etching alone, and KOH etching followed by SiO2 passivation with the SiO2 prepared by the sol-gel technique. In addition, the effects of Ag/SiO2 core/shell nanoparticles prepared by sol-gel were studied for all surface treatments. For as etched nLEDs, the Internal Quantum Efficiency (IQE) of photoluminescence was low, 5.5%, because of the impact of surface damage introduced by RIE. KOH etching and KOH plus SiO2 passivation produced an increase of IQE to respectively 5.7 and 6.8%. When the Ag/SiO2 core/shell nanoparticles known to produce localized surface plasmon resonance at the wavelength well-matched to the light emission from the MQWs were added to the polymer filling the gaps between the MQW nanorods, the result was found to depend on finding a proper balance between the enhancement due to the interaction Ag/SiO2 nanoparticles adjacent to the MQW nanorods and the absorption by “idle” Ag/SiO2 particles in the bulk of the polymer. When optimal concentrations of LSP NPs giving rise to maximal enhancement of the MQW PL intensity were used, a considerable improvement of performance was obtained, with IQE of 10.6%.