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In this study, wavelength-dependent efficiency droop phenomena in InGaN-based light-emitting diodes (LEDs) by a reduced effective active region volume were investigated. Different effective active region volumes can be extracted from theoretical fitting to the efficiency-versus-current curves of standard high efficiency InGaN near-ultraviolet, blue, and green LEDs. It has been found that the effective volume of the active region reduces more significantly with increasing emission wavelength, resulting in a lower onset-droop current density, as well as a more severe droop. Increasing the quantum well (QW) thickness to reduce carrier density is proposed as an effective way to alleviate the efficiency droop.

Perovskite solar cells (PSCs) have attracted great attention due to their low cost and high power conversion efficiency (PCE). However, the defects and grain boundaries in perovskite films dramatically degrade their performance. Here, we show a two-step annealing method to produce mesoporous PbI 2 films for growth of continuous, pinhole-free perovskite films with large grains, followed by additional ethanol vapor annealing of perovskite films to reduce the defects and grain boundaries. The large perovskite grains dramatically suppress the carrier recombination, and consequently we obtain ZnO-nanorod-based PSCs that exhibit the best efficiency of 17.3%, with high reproducibility. [ABSTRACT FROM AUTHOR]

As an intermediate band (IB) originating from discrete nitrogen (N) levels is formed in GaP:N with increasing N concentration, GaP1− xN x alloy is considered to be a promising candidate for IB-type solar cells. We studied the IB luminescence of a GaP1− xN x with 0.56% N and detected carrier recombination (CR) levels by superposing a below-gap excitation (BGE) light of 1.17 eV. We resolved a high-energy component of 2.15 eV in the IB luminescence, Ihigh, from total luminescence intensity Iall. With increasing the BGE density at fixed temperature of 5 K, the amount of decrease in Ihigh was distinctly smaller than that of simple temperature rise without the BGE at the same Iall value. We conclude that the observed intensity change of the IB luminescence due to the BGE comes not from thermal activation, but from optical excitation among the IB, conduction band, and CR levels in GaP1− xN x. It is of primal importance to understand CR levels toward determining their origins and eliminating them for realization of efficient IB-type solar cells. [ABSTRACT FROM AUTHOR]

To achieve high-performing perovskite solar cells (PSCs) interfacial engineering of the perovskite thin film and charge carrier-selective layers is vital for fast extraction of photogenerated electrons and holes, and the suppression of electron-hole recombination. Herein, a glucose-assisted self-assembly solvothermal protocol is reported to prepare electron-rich TiO 2 thin films as effective electron transport layers exhibiting enhanced electron mobility. Bilayer structured CH 3 NH 3 PbI 3 perovskite films are spontaneously formed, consisting of a flat and dense bottom layer forming the TiO 2 /CH 3 NH 3 PbI 3 planar heterojunction and a textured and porous top layer elongating in the vertical direction forming the CH 3 NH 3 PbI 3 /spiroMeOTAD bulk heterojunction. The integrated planar and bulk dual heterojunction based PSCs are efficient in light harvesting and charge collection, and thus yield power conversion efficiencies up to 17.75% and a stabilized power output above 17.20%. Integrating both planar and bulk heterojunctions into a PSC assembly provides an effective approach for fabricating highly efficient perovskite optoelectronic devices. [ABSTRACT FROM AUTHOR]

Formation energies, charge transitions levels, and quasiparticle defect states of the tellurium antisite ( Te Cd ) in CdTe are addressed within the DFT + GW formalism. We find that ( Te Cd ) induces a (+2/0) deep level at 0.99 eV above the valence band maximum, exhibiting a negative-U effect. Moreover, the calculated zero-phonon line for the excited state of ( Te Cd ) 0 corresponds closely with the ∼1.1 eV band, visible in both luminescence and absorption experiments. Our results differ from previous theoretical studies, mainly due to the well-known band gap error and the incorrect position of the band edges predicted by standard DFT calculations. [ABSTRACT FROM AUTHOR]

All-oxide solar cells are presently attracting extensive research interest due to their excellent stability, low-cost and non-toxicity. However, the band gap of metal oxides is lack of effective optimization and results in poor photovoltaic performance, thus hindering their practical applications. In this work, Co 3 O 4 was investigated for application as a photo-absorber in all-oxide solar cells, and its band gap was optimized by introducing Li dopant into the spinel structure. Li x Co 3−x O 4 nanoparticles, prepared via the hydrothermal method, were homogenously coated onto TiO 2 mesoporous films, which were then used to fabricate planar heterojunction TiO 2 /Li x Co 3−x O 4 solar cells (SCs). The effects of Li-doping on the heterojunction solar cell performance were further investigated. The findings revealed that the incorporation of Li ions into Co 3 O 4 led to a significant enhancement in short-circuit current density (J sc ). Remarkably, a high open-circuit voltage (V oc ) of 0.70 V was also achieved. Besides, reasons for the enhanced cell performance are the narrower band gap, reduced photogenerated carrier recombination and the more favorable energy band structure as compared with SCs assembled from pure Co 3 O 4 . [ABSTRACT FROM AUTHOR]

Hybrid silicon/organic solar cells have been recently extensively investigated due to their simple structure and low-cost fabrication process. However, the efficiency of the solar cells is greatly limited by the barrier height as well as the carrier recombination at the silicon/organic interface. In this work, hydrochloroplatinic acid (HPtCl) is employed into the poly(3,4-ethlenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution, and the work function (WF) of the PEDOT:PSS layer has been successfully improved. Based on the Pt-modified PEDOT:PSS layer, the efficiency of the silicon/PEDOT:PSS cell can be increased to 11.46%, corresponding to ~20% enhancement to the one without platinum (Pt) modification. Theoretical and experimental results show that, when increasing the WF of the PEDO:PSS layer, the barrier height between the silicon/PEDOT:PSS interface can be effectively enhanced. Meanwhile, the carrier recombination at the interface is significantly reduced. These results can contribute to better understanding of the interfacial mechanism of silicon/PEDOT:PSS interface, and further improving the device performance of silicon/organic solar cells. [ABSTRACT FROM AUTHOR]

We investigate two-photon luminescence (TPL) of single CdSe nanowires (NWs) excited by tightly focused cylindrical vector beams of 150 fs pulses, achieving an optical resolution better than λ/4. Comparing the TPL images recorded by scanning the nanowires through the focal fields created either by a radially or an azimuthally polarized vector beam we observe a distinct anisotropic excitation efficiency which depends on the orientation of the electric field component with respect to the nanowire. The excitation anisotropy of the linear photoluminescence (PL) and TPL can directly be derived from the respective image patterns. Our results show that the highest TPL signal from a single NW is detected when the electric excitation field is parallel to the long axis of the NW, i.e. about one order of magnitude stronger than that excited along the short axis. We attribute the TPL to an emission mechanism based on the recombination of free carriers, which exhibits a fourth order excitation power dependence in low power regime and a second order power dependence in high power regime. [ABSTRACT FROM AUTHOR]

In the typical solution-based synthesis of colloidal quantum dots (QDs), it always resorts to some surface treatment, ligand exchange processing or post-synthesis processing, which might involve some toxic chemical regents injurious to the performance of QD sensitized solar cells. In this work, the CuInS 2 QDs are deposited on the surface of one-dimensional TiO 2 nanorod arrays by the pulsed laser deposition (PLD) technique. The CuInS 2 QDs are coated on TiO 2 nanorods without any ligand engineering, and the performance of the obtained CuInS 2 QD sensitized solar cells is optimized by adjusting the laser energy. An energy conversion efficiency of 3.95% is achieved under one sun illumination (AM 1.5, 100 mW cm −2 ). The improved performance is attributed to enhanced absorption in the longer wavelength region, quick interfacial charge transfer and few chance of carrier recombination with holes for CuInS 2 QD-sensitized solar cells. Moreover, the photovoltaic device exhibits high stability in air without any specific encapsulation. Thus, the PLD technique could be further applied for the fabrication of QDs or other absorption materials. [ABSTRACT FROM AUTHOR]

CuInS 2 /ZnS (CIS/ZnS) core/shell quantum dots (QDs) with various Cu/In ratios were synthesized using the hot-injection method, and their photoluminescence (PL) properties were investigated by measuring steady-state and time-resolved PL spectroscopy. The emission peak of the CIS/ZnS QDs were tuned from 680 to 580 nm by decreasing the Cu/In precursor ratio from 1/1 to 1/9. As the Cu/In ratio decreases, the PL lifetimes and PL quantum yields (QYs) of CIS/ZnS core/shell QDs increased firstly and then decreased. Two dominant radiative recombination processes were postulated to analyze composition-dependent PL properties, including the recombination from a quantized conduction band to deep defects state and donor-acceptor pair (DAP) recombination. The decrease of PL efficiency resulted from high density defects and traps, which formed at the interface between CIS core and ZnS shell due to the large off-stoichiometry composition. The PL intensity and peak energy for CIS/ZnS core/shell QDs as a function of temperature were also provided. The thermal quenching further confirmed that the PL emission of CIS/ZnS QDs did not come from the recombination of excitons but from the recombination of many kinds of intrinsic defects inside the QDs as emission centers. [ABSTRACT FROM AUTHOR]

Via temperature-dependent time-resolved photoluminescence spectroscopy, we investigate the radiative and nonradiative recombination processes in thin (quantum well widths of about 1.5 nm) a-plane, m-plane, ( [ABSTRACT FROM AUTHOR]

We present results on photoexcited carrier lifetimes in few-layer transition metal dichalcogenide MoS2 using nondegenerate ultrafast optical pump-probe technique. Our results show a sharp increase of the carrier lifetimes with the number of layers in the sample. Carrier lifetimes increase from few tens of picoseconds in monolayer samples to more than a nanosecond in 10-layer samples. The inverse carrier lifetime was found to scale according to the probability of the carriers being present at the surface layers, as given by the carrier wave function in few layer samples, which can be treated as quantum wells. The carrier lifetimes were found to be largely independent of the temperature, and the inverse carrier lifetimes scaled linearly with the photoexcited carrier density. These observations are consistent with defect-assisted carrier recombination, in which the capture of electrons and holes by defects occurs via Auger scatterings. Our results suggest that carrier lifetimes in few-layer samples are surface recombination limited due to the much larger defect densities at surface layers compared with the inner layers. [ABSTRACT FROM AUTHOR]

Enhancement of internal quantum efficiency (IQE) in InGaN quantum wells by insertion of a superlattice interlayer and applying the pulsed growth regime is investigated by a set of time-resolved optical techniques. A threefold IQE increase was achieved in the structure with the superlattice. It was ascribed to the net effect of decreased internal electrical field due to lower strain and altered carrier localization conditions. Pulsed MOCVD growth also resulted in twice higher IQE, presumably due to better control of defects in the structure. An LED (light emitting diode) structure with a top p-type contact GaN layer was manufactured by using both growth techniques with the peak IQE equal to that in the underlying quantum well structure. The linear recombination coefficient was found to gradually increase with excitation due to carrier delocalization, and the latter dependence was successfully used to fit the IQE droop. [ABSTRACT FROM AUTHOR]

Although Cu(In,Ga)Se 2 (CIGS) solar cells have the highest efficiency of any thin-film solar cell, especially when sodium is incorporated, the fundamental device properties of ultrafast carrier transport and recombination in such cells remain not fully understood. Here, we explore the dynamics of charge carriers in CIGS absorber layers with varying concentrations of Na by femtosecond (fs) broadband pump-probe reflectance spectroscopy with 120 fs time resolution. By analyzing the time-resolved transient spectra in a different time domain, we show that a small amount of Na integrated by NaF deposition on top of sputtered Cu(In,Ga) prior to selenization forms CIGS, which induces slower recombination of the excited carriers. Here, we provide direct evidence for the elongation of carrier lifetimes by incorporating Na into CIGS. [ABSTRACT FROM AUTHOR]

In this paper, we employ the drift–diffusion model to investigate the carrier recombination lifetime effects on the performance of the InGaAs/GaAs quantum dot intermediate band solar cells. In our model, we use experimentally achieved material parameters such as the absorption coefficients, carrier mobilities, quantum dot concentration, etc. for quantum dots and host material. Proper operation of the QD-IBSC would require that no charge carriers are allowed to be extracted from the quantum dot confined levels or intermediate bands. This would reduce the power output of the IBSC and thus the conversion efficiency. But carrier recombination in intermediate band and carrier transition between intermediate bands are an important parameter in the operation of QD-IBSC. In this study, we propose a model that by using the possible values of carrier recombination lifetimes, the effective recombination rate and photocurrent processes in active region of the cell can be calculated. By using the three values of the recombination life time, V oc , j sc and efficiency of the cell have been calculated and it was shown that higher value of recombination lifetime leads to the higher efficiency due to increase the j sc , but not significant increase occurred in V oc . This paper indicates that in experimental design and fabrication of InGaAs/GaAs based QD-IBSC, the recombination lifetime of carriers should be controlled, which if the value of recombination lifetimes in fabricated cell is too low, then performance of the cell will be lower than reference cell without QDs. [ABSTRACT FROM AUTHOR]

It is well known that temperature is a key factor affecting the performance of solar photovoltaic cells. The temperature affects the light-trapping ability of the cell surfaces, displacement and recombination of minor carriers in the cells. This paper is to examine how the temperature affects the conversion performance of nanostructured silicon thin-film solar cells by means of the photoelectric coupling model. Two typical nanostructures such as nano-pillars (NPillars) and nano-holes (NHoles) are involved. The effects of temperature-dependent optical and electrical properties on the cell performance are investigated. It is found that the effect of increase in temperature is positive for optical properties whereas that is negative for electrical properties and the slight increase of optical absorption cannot compensate the dramatic decrease of electrical loss in nanostructured silicon thin-film solar cells as the temperature increases. Consequently, the photon-electric conversion efficiency decreases with the increase in temperature. [ABSTRACT FROM AUTHOR]

The combined temporally, spatially and spectrally-resolved optical techniques, namely the photoluminescence, light induced transient grating, and differential reflectivity were used for investigation of excitation-dependent PL efficiency, exciton lifetime, and diffusion coefficient in Si-doped Al-rich multiple quantum wells and epilayers at various temperatures. Novel features of carrier recombination and in-plane diffusion were observed. Low-excitation radiative lifetime of 1-2 ns was found temperature-independent in 80-150 K interval, while it sublinearly decreased with excitation at excess carrier densities above 1018 cm−3. The lifetime decrease correlated with the increase of diffusion coefficient, indicating excitation-enhanced delocalization of localized excitons and therefore enhanced capture to nonradiative centers. The droop of photoluminescence efficiency with excitation was the strongest at 80-150 K due to strong delocalisation at low-temperatures, while at higher temperatures the thermal activation prevailed in photoluminescence excitation dependence. The photoluminescence efficiency quenching at T > 200 K provided rather high activation energies of ∼100 and 160 meV for Al-rich multiple quantum wells and epilayers, correspondingly. [ABSTRACT FROM AUTHOR]

13.56 MHz capacitance coupled Ar plasma irradiation at 50 W for 120 s caused serious damage at SiO 2 /Si interfaces for n-type 500-μm-thick silicon substrates. The 635-nm-light induced minority carrier effective lifetime ( τ eff ) was decreased from 1.7 × 10 −3 (initial) to 1.0 × 10 −5 s by Ar plasma irradiation. Moreover, the capacitance response at 1 MHz alternative voltage as a function of the bias voltage ( C – V ) was changed to hysteresis characteristic associated with the density of charge injection type interface traps at the mid gap ( D it ) at 9.1 × 10 11 cm −2 eV −1 . Subsequent 940-nm laser annealing at 3.7 × 10 4 W/cm 2 for 4.0 × 10 −3 s markedly increased τ eff to 1.7 × 10 −3 s and decreased D it to 2.1 × 10 10 cm −2 eV −1 . The hysteresis phenomenon was reduced in C – V characteristics. Laser annealing effectively decreased the density of plasma induced carrier recombination and trap states. However, laser annealing with a high power intensity of 4.0 × 10 4 W/cm 2 seriously caused a thermal damage associated with a low τ eff and a high D it with no hysteresis characteristic. [ABSTRACT FROM AUTHOR]

A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties. [ABSTRACT FROM AUTHOR]

17.3% efficient black silicon (b-Si) solar cell without antireflection coating was achieved via tetramethylammonium hydroxide (TMAH) etching after the formation of the diffusion emitter. Large area (156 × 156 mm 2 ) b-Si wafers were prepared by silver-nanoparticle-assisted etching on pyramid-structured silicon wafers. The modification of nanostructures of silicon surface by TMAH etching suppresses the surface recombination and Auger recombination at and near the emitter surface, and the effective minority carrier lifetime of the b-Si solar cells was improved from 10.7 μs to 20.8 μs. Although the average reflectance of the b-Si solar cell slightly increases from 2.38% to 2.71% via the process of TMAH etching, it is a small loss compared with the beneficial impact of the improvement of the carrier recombination lifetime. As a result, the internal quantum efficiency at short wavelength region was improved through the TMAH etch treatment, which was a main limiting factor for the efficiency of b-Si solar cells. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) measurements were performed in Si/Si1−xGex nanostructures with a single Si0.92Ge0.08 nanometer-thick layer incorporated into Si/Si0.6Ge0.4 cluster multilayers. Under pulsed laser excitation, the PL decay associated with the Si0.92Ge0.08 nano-layer is found to be nearly a 1000 times faster compared to that in Si/Si0.6Ge0.4 cluster multilayers. A model considering Si/SiGe hetero-interface composition and explaining the fast and slow time-dependent recombination rates is proposed. [ABSTRACT FROM AUTHOR]

Room-temperature luminescence properties of dense electron-hole plasma were studied in GaN epilayers grown by various techniques (by LUMILOG grown on sapphire substrate, by AIXTRON via a MOCVD reactor grown on SiO and by UNIPRESS by the MOCVD technique grown on sapphire). By studying emission properties of plasma in lateral "thin stripe" excitation geometry the values of the threshold of the stimulated emission were estimated. A linear decrease of the stimulated emission threshold with a decrease in the density of the dislocations in GaN layers was observed. This dependence was shown to be mainly contributed by a decrease in carrier lifetime, while the impact of variation in carrier diffusion coefficient was found to be minor. Incorporation of iron into GaN layer significantly increased the stimulated emission threshold. The role of the light-scattering losses on the values of the stimulated emission threshold was discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Combined differential reflectivity and transmittivity setup was constructed. [•] Non-equilibrium carrier dynamics was studied in a thick 3C-SiC wafer. [•] Optical delay decays provided nonlinear and surface recombination rates. [•] Electrical delay decays provided bulk defect limited lifetimes. [•] Impact of near-surface and surface defects was revealed. [Copyright &y& Elsevier]

We present a comprehensive study of photoexcited carrier dynamics in differently grown InGaN/InGaN multiple quantum well (MQW) structures, modified by insertion of a wide interlayer structure and subsequent growth of differently shaped quantum wells (rectangular, triangular, trapezoidal). This approach of strain management allowed the reduction of dislocation density due to gradually increasing In content in the interlayer and shaping the smooth quantum well/barrier interfaces. A set of c-oriented MQW structures emitting at 470 nm were grown at Vilnius University, Institute of Applied Research, using a closed coupled showerhead type MOCVD reactor. Photoluminescence (PL) spectra of MQW structures were analysed combining continuous wave and pulsed PL measurements. Reactive ion etching of the structures enabled discrimination of PL signals originated in the InGaN interlayer structure, underlying quantum wells, and quantum barriers, thus providing growth-related conditions for enhanced carrier localization in the wells. Time-resolved PL and differential transmission kinetics provided carrier lifetimes and their spectral distribution, being the longest in triangular-shape QWs which exhibited the highest PL intensity. The light-induced transient grating (LITG) technique was used to determine the spatially averaged carrier lifetime in the entire heterostructure, in this way unravelling the electronic quality of the LED internal structure at conditions similar to device performance. LITG decay rates at low and high excitation energy densities revealed increasing with photoexcitation nonradiative recombination rate in the triangular and trapezoidal wells. [ABSTRACT FROM AUTHOR]

Abstract: This article presents a novel magnetotransistor based on carrier recombination–deflection effect for detecting magnetic field in three dimensions (B X, B Y, and B Z) by relying on the difference between base and collector currents (∆I CB). This device used low biasing current. It was designed and fabricated using CMOS fabrication technology. The device structure consisted of one emitter, 4 collectors and 4 bases. All four collector terminals were connected with each other. The same was true for the four base terminals. LOCOS oxide was grown to surround the emitter area to limit lateral carrier loss, and therefore reducing the overall biasing current. The experiment showed that, at 0.2mA of biasing current, the B X, B Y and B −Z direction sensitivity to magnetic field within the range of 0-400mT are 2, 5 and 14.5%/T, respectively. This research on the merged magnetotransistor produced magnetic sensors with small size, high performance with wide range of applications. [Copyright &y& Elsevier]

We report rapid laser-induced passivation of the silicon surface. When the top surfaces of n-type 500-μm-thick silicon substrates with surfaces coated with 100 nm thermally grown SiO2 layers (initial samples) were irradiated with Ar plasma at 50 W for 120 s, the 635-nm-light induced minority carrier effective lifetime τeff decreased from 1.7×10-3 (initial) to 1.7×10-5 s because Ar plasma caused substantial carrier recombination defect states at the silicon surfaces, τeff was markedly increased to 1.7×10-3 s by 940 -nm-semiconductor laser irradiation at 3.57×10-4 W/cm2 for 4 ms. Laser heating effectively decreased the density of plasma induced carrier recombination defect. However, laser heating of the initial sample at 4.0×10 W/cm2 decreased τeff from 2.2×10-3 (initial) to 1.7×10-4 s. Additional laser heating at 3.70×10-4 W/cm2 increased τeff to 3.9×10-4 s-and it partially cured laser induced carrier recombination defects. [ABSTRACT FROM AUTHOR]

The performance improvements of adding InAs quantum dots (QDs) in the middle subcell of a lattice matched triple-junction InGaP/InGaAs/Ge photovoltaic device are studied using the simulated external quantum efficiency, photocurrent, open circuit voltage, fill factor, and efficiency under standard testing conditions. The QDs and wetting layer are modeled using an effective medium consisting of trap states for the former and low confinement potentials for the latter. Although the efficiency stabilizes for more than 100 layers of QDs for the structure studied, the efficiency achieves an absolute efficiency of 31.1% under one sun illumination for 140 layers of QDs. This corresponds to a relative increase of 1.3% compared with a control structure with no QD layers. The performance of the device depends intricately on the magnitude of the confinement potentials representing the wetting layer. [ABSTRACT FROM PUBLISHER]

A CuSe intermediate layer (IL) is prepared between CZTSSe and Mo electrode to decay the carrier recombination on the rear surface of the CZTSSe absorber. The power conversion efficiency (PCE) can be increased from 7.52% to 10.09% by optimizing the thickness of CuSe IL. The increased PCE comes from improvement in filling factor (FF), short-circuit current density (J SC), and open-circuit voltage (V OC), and their contribution percent is calculated to be 63.08%, 24.83%, and 12.09%, respectively. It is demonstrated that boosted FF is mainly due to decreased reverse saturation current density (J 0), raised J SC owing to higher photogenerated current density (J L), and enhanced V OC caused by decreased J 0 and higher J L. The contribution percent of (ideal factor (A), J 0), J L , R s , and shunt resistance (R sh) to increased PCE is calculated to be 60.84%, 27.41%, 10.33%, and 1.42%, respectively. By experimental characterization and SCAPS-1D simulation, it is suggested that decreased J 0 results from the formation of passivation field and high electron potential barrier at the rear surface of CZTSSe due to the addition of suitable thickness CuSe IL, higher J L from the increase in width of the depletion region of CZTSSe/CdS, lower R s from decrease in thickness of Mo(S, Se) 2 , and bigger R sh from improved crystal quality of CZTSSe absorber. [Display omitted] • PCE of CZTSSe solar cells was improved from 7.52% to 10.09% by optimizing the CuSe intermediate layer thickness. • CuSe was produced between CZTSSe and Mo electrode through selenizing CZTS/Cu/Mo/SLG. • SCAPS-1D simulation and experimental study demonstrate decreased recombination on the rear surface of absorber. • The extent of contribution of (A, J 0), J L , R s , and R sh to the increased PCE was calculated. [ABSTRACT FROM AUTHOR]

Highlights: [•] The photoconductivity of ZnO nanorod array exhibits a long time degradation process. [•] A novel charge storage property is observed in ZnO nanorod array. [•] The photogenerated carrier transport models in ZnO film are established. [•] Different charge state oxygen vacancies decide the photogenerated carrier lifetime. [•] The neutral oxygen vacancy contributes to the charge storage of ZnO nanorod array. [Copyright &y& Elsevier]

We deposited a p-i-n structure device with alternative amorphous Si (a-Si) and amorphous SiC (a-SiC) multilayers as an intrinsic layer in a plasma-enhanced chemical vapor deposition (PECVD) system. A KrF pulsed excimer laser-induced crystallization of a-Si/a-SiC stacked structures was used to prepare Si quantum dots (Si QDs)/SiC multilayers. The formation of Si QDs with an average size of 4 nm was confirmed by Raman spectra, whereas the layered structures were revealed by cross-sectional transmission electron microscopy. Electroluminescence (EL) devices containing Si QDs/SiC multilayers embedded in a p-n junction were fabricated, and the device performance was studied and compared with the reference device without the p-i-n structure. It was found that the turn-on voltage was reduced and that luminescence efficiency was significantly enhanced by using the p-i-n device structure. The recombination mechanism of carriers in a Si-QD-based EL device was also discussed, and the improved device performance can be attributed to the enhanced radiative recombination probability in a p-i-n EL device. [ABSTRACT FROM PUBLISHER]

Abstract: The D–π–A organic dyes which feature diphenylthienylamines as the donors and cyanoacrylic acid as the acceptors, are carefully examined. Comprehensive spectral response analysis and transient techniques are exploited to investigate the effects of various functionalized π-bridge and hexyloxy side chains in donor moieties on carrier injection efficiencies, electron diffusion length and dye-regeneration efficiencies. Retarded charge recombination of /electrolytes+ is found in molecules with the hexyloxy chains and diphenyl-substituted dithienosilole groups. However, regeneration rate is revealed as being slower with the larger sensitizer structure and the higher HOMO levels. A clear trade-off between charge recombination and dye regeneration is found and should be taken into account in future molecular designs of D–π–A dyes. [Copyright &y& Elsevier]

Cuprous oxide (Cu 2 O) films are electrodeposited on fluorinated tin oxide (FTO) substrates with controlled crystallographic orientation and optimized film thickness. The Cu 2 O films exhibit a (100)-to-(111) texture change and a pyramid-to-cuboidal crystallite morphology transformation by increasing the electrodeposition current density. The cuboidal crystallites enclosed by (100) sidewalls and (111) truncated surfaces demonstrate better photoelectrochemical property than the pyramid crystallites. By introducing a copper(I) telluride (Cu 2 Te) layer in between Cu 2 O and FTO, the photocurrent density increases 70% for the (111)-textured Cu 2 O film in a 1 M Na 2 SO 4 solution under AM1.5 G illumination. The enhancement is mainly attributed to the improved separation of photocarriers in the illuminated Cu 2 O film by pumping hole carriers to the Cu 2 Te layer. In contrast to typical electron pathway management, this study provides an alternative route to improve the photoelectrochemical performance of Cu 2 O-based photocathodes through hole pathway modification.

In nominally undoped layered TlGaSe2 crystals the trapping centers have been investigated by photo-induced current transient spectroscopy (PICTS). Five acceptor and donor traps have been detected. Quite large magnitudes of capture cross-sections for donor traps at 0.23 and 0.45 eV have been determined. The depth-resolved free-carrier absorption (FCA) technique has been applied for the investigation of the majority hole lifetime, τR, at 295 and 77 K. The pronounced τR reduction with increasing injection level is attributed to the trapping effect of the minority electrons which provides a way of estimating trap centers concentration. A moderate τR variation across layer planes is observed but no carrier diffusion related to the recombination on the external crystal surfaces is detected. Moreover, abnormally sharp τR drop is found for carrier concentration above 1017 cm−3. The possibility of excess hole and electron special separation due to compositional stacking faults and the successive their enhanced recombination at high excess carrier concentrations is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Delayed EL measurements are used to elucidate carrier recombination and light emission mechanism in phosphorescent organic light emitting devices (PhOLEDs) based on 4,4′-bis(9-carbazolyl)-1,1′-biphenyl (CBP) and fac-tris(2-phenylpyridine) iridium (Ir(ppy)3) host:guest system. The results show that changing the thickness of the emitting layer (EML) leads to marked changes in charge-trapping and host–host triplet–triplet-annihilation (TTA) patterns, suggesting that carrier transport and recombination processes change depending on EML thickness. The results suggest a change in carrier recombination and exciton formation mechanism, depending on EML thickness, from a scenario (for EMLs <20nm) in which recombination occurs mostly on the guest rather than the host thus creating excitons directly on the guest, and hence is not strongly influenced by host-to-guest energy transfer; to another scenario (for EMLs >20nm) where carrier recombination and exciton creation on the host is not negligible, and hence also the role of host-to-guest energy transfer. [Copyright &y& Elsevier]

The field of SiC electronics has progressed rapidly in recent years, but certain electronic properties remain poorly understood. For example, a consensus has not been reached as to the specific point defects which limit minority carrier recombination, and little is known about defects which limit generation lifetimes. This paper investigates generation lifetimes using the pulsed MOS capacitor technique and compares the results with defect densities, recombination lifetimes, and Schottky diode characteristics in the same material for the first time. Carrier generation lifetimes in 4H-SiC epilayers range from less than 1 ns to approximately 1 µs and depend strongly on measurement conditions and data interpretation. They are limited by dislocations only at densities higher than 106 cm-2. The only point defect that is theoretically capable of limiting generation lifetime to the levels currently observed in 4H-SiC is EH6/7. However, this defect cannot account for the case where generation lifetimes are lower than recombination lifetimes in the same area. This is not seen in silicon and seems to be inconsistent with theory. Possible reasons for these perplexing results are discussed, and it is attempted to form a framework with which further understanding of the significance of carrier generation lifetime measurements in SiC can be achieved. [ABSTRACT FROM AUTHOR]