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Carrier localization effect has been observed in GaN/AlGaN multiquantum wells (MQWs) by analyzing the temperature dependent photoluminescence (PL) results. Specifically, two neighbouring peaks can be seen in the PL spectra with an abnormal variation when increasing the temperature. A conduction band model with two minimal potentials corresponding to two carrier localizations is proposed to explain the PL spectra. [ABSTRACT FROM AUTHOR]

Analytical models of the pin diode in a small-current operation are not known yet. This article presents a simple analytical model of the pin diode operation with its confirmation by a numerical simulation. At the onset, carrier recombinations are not included for the sake of simplicity. The exact JF-VF characteristic $[J_{F} \propto \hbox{exp}(V_{F}/kT)]$ could have been induced only by accounting for the Boltzmann distribution of each carrier across the junctions and the diffusion current of each minority carrier in a p-anode or n-cathode. Based on this new model, the modifications of hole–electron densities product (nenh) across junctions, a rough estimation of the large operational current, its carrier distributions, and the effect of carrier recombination on the carrier distribution are plainly estimated and are also compared with the simulation results. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(4): 47–56, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20844 [ABSTRACT FROM AUTHOR]

Abstract: Effects of thermal annealing on carrier recombination in lattice-mismatched InGaAs solar cells on GaAs substrates were investigated. Thermal annealing to the graded buffer layer was effective to increase the minority carrier lifetime in the solar cell layer. Electron beam-induced current (EBIC) measurements revealed that the density of dark line defects decreased after the thermal annealing, but dark spot defects were newly generated. We conclude that dark line defects were primary responsible for the high recombination in the lattice-mismatched InGaAs solar cells. The origin of dark spot defects was discussed and it was found that they were associated with the lattice mismatch between the InGaP back surface field (BSF) layer and the InGaAs cell layer. [Copyright &y& Elsevier]

Calculations based on our Monte Carlo code for the transport of electrons and ions in silicon are presented. The code follows the trajectories of all secondary electrons down to a very low cut-off energy (1.5 eV). The spatial and temporal distributions of the deposited energy around ion tracks in silicon are also calculated. The prompt electrical fields generated by the charges at the early stage of the track evolution are evaluated, taking into account carrier recombination. Using the statistics of the energy deposition events in small sensitive volumes, we find that the SEE cross sections in modern devices depend on the ion energy, in addition to its LET. [ABSTRACT FROM PUBLISHER]

Carrier dynamics in silicon photonic crystal (PhC) nanocavities are studied numerically. The results agree well with previous experimental demonstrations. It is shown that the presence of carrier diffusion makes fast switching possible, which is an advantage of nanocavity switches over other types of larger carrier based nonlinear optical switches. In particular, diffusion is effective in PhC nanocavity switches, which makes the switching recovery time even faster than that of silicon waveguide-based optical switches. In addition, calculations suggest that the thermo-optic effect can be reduced if the carriers are extracted within a few 100 ps by introducing a p-i-n structure. [ABSTRACT FROM PUBLISHER]

Abstract: A traditional hole-transporting (HT) material, 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) was used as the host to fabricate a blue organic light-emitting diode (OLED) in which the blue dopant emitter is 2,5,8,11-tetra-t-butyl-perylene (TBP) and the another NPB layer adjusted to thinner host was also used as the HT-layer. The blue electroluminescent (EL) was proved to be originated from the narrower doped layer and the adjacent NPB HT-layer. Compared with the previous blue EL devices based on TBP dopant, the performances of the blue OLED were improved by using a thinner NPB host layer. The blue OLED shows higher efficiency and better blue color saturation, such as the device behaving a maximum efficiency of 4.6cd/A, CIE color coordinates of x =0.136 and y =0.173 at a bias of 5V, and a peak luminance of 11,500cd/m2 at a bias of 20V. The operation mechanism of the blue device was also discussed. [Copyright &y& Elsevier]

In this paper, we report that low-density InAs/GaAs quantum dots (QDs) can be formed by postgrowth annealing the samples with 1.5-monolayer (ML) InAs coverage, which is thinner than the critical layer thickness for the Stranski-Krastanov growth. The annealing procedure was performed immediately after the deposition of the InAs layer. The effects of annealing time and annealing temperature on the dot density, dot size, and optical characteristics of the QDs were investigated. The optimum annealing conditions to obtain low-density QDs are longer than 60 s and higher than 500degC . Meanwhile, no luminescence can be observed for the wetting-layer, which may suggest that the postgrowth annealing will make the wetting layer thinner and thus reduce the effects of wetting layer on carrier relaxation and recombination. On the other hand, we observe that a decrease of the PL intensity at the annealing conditions of 60 s and 515degC , which is possibly due to the increasing surface dislocations resulted from the In adatom desorption at higher annealing temperature. [ABSTRACT FROM PUBLISHER]

Molecular dye dispersed solution processable blue emitting organic light-emitting devices have been fabricated and the resulting devices exhibit efficiency as high as 25 cd/A. With down-conversion phosphors, white emitting devices have been demonstrated with peak efficiency of 38 cd/A and luminous efficiency of 25 lm/W. The high efficiencies have been a product of proper tuning of carrier transport, optimization of the location of the carrier recombination zone and, hence, microcavity effect, efficient down-conversion from blue to white light, and scattering/isotropic remission due to phosphor particles. An optical model has been developed to investigate all these effects. In contrast to the common misunderstanding that light out-coupling efficiency is about 22% and independent of device architecture, our device data and optical modeling results clearly demonstrated that the light out-coupling efficiency is strongly dependent on the exact location of the recombination zone. Estimating the device internal quantum efficiencies based on external quantum efficiencies without considering the device architecture could lead to erroneous conclusions [ABSTRACT FROM PUBLISHER]

All-optical switches based on optical carrier injection in high-index-contrast Si/SiO2 split-ridge-waveguide (SRW) couplers are analyzed. The waveguide devices are suitable for the construction of low-loss optical switch matrices as well as fast optical switching. These devices exhibit robustness against fabrication tolerances, improved heat sinking, good carrier confinement, and high uniformity in transmission over the entire C-band of optical communications, in contrast to comparable devices based on buried or ridge waveguides. Reasonably low electrical switching power of 1-10 mW is predicted for switching frequencies of 1 MHz to 1 GHz. Carrier recombination measurements in thin Si layers passivated with different oxide layers confirm the feasibility of the designed switches and modulators [ABSTRACT FROM PUBLISHER]

We investigate the below and above threshold frequency response of InGaAsN lasers with different nitrogen content. This is accomplished through detailed analysis of the small signal modulation response of the laser diodes using a comprehensive model based on rate equations and that incorporates the effect of parasitics. For below threshold conditions the model is instrumental in separating the contributions from the parasitics (more severe at low bias) and carrier recombination (predominant at higher bias) to the measured carrier lifetime. It is found that the addition of nitrogen reduces the recombination lifetime, mainly as a result of a four-fold increase in monomolecular recombination which predominates even near threshold. For bias above threshold the analysis compares electrical versus optical modulation frequency responses and concludes that resonance frequency and damping extracted from the electrical modulation responses are significantly influenced by the device parasitics. Instead, it is shown that optical modulation traces allow extraction of a relaxation frequency that is shaped only by the stimulated processes in the laser active region. Even in this case, the damping is found to be affected by the parasitics. When compared with nitrogen free lasers, a reduction in the resonance frequency is observed, while the damping is not altered. The former arises from a factor of ∼2.5 decrease in the combined effect of the differential gain and carrier transport parameters. The latter reflects the more significant contribution of the parasitics to the damping. [ABSTRACT FROM PUBLISHER]

The material extensively used for construction of dye-sensitized solar cells is TiO2. Similar cells made from other familiar semiconductor oxide materials such as SnO2 and ZnO have yielded efficiencies far below the values corresponding to TiO2-based cells. The indication is that electrons injected to s-band materials (SnO2) are more susceptible to recombination compared to d-band materials (TiO2). However, an impressive improvement in efficiency has been noticed when SnO2 crystallites are coated with ∼0.5–1 nm ultra-thin shells of high band gap oxides which act as a barrier against recombination. Naturally a barrier would also lower the electron injection efficiency and oxide barriers of thickness ∼0.5–1 nm were noted to lower the efficiency of cells based on TiO2. Contrary to our observation, reports in literature gives instances of obtaining higher efficiencies when TiO2 crystallites in the film are coated with other oxide materials. In order to elucidate this problem an extensive series of experiments were conducted by coating TiO2 crystallites with outer shells of different materials of varying thickness. Although there is some evidence for marginal improvement, efficiencies distinctively above the optimized TiO2 could not be achieved by this technique. Experimental details and difficulties involved in making a clear conclusion are discussed. [Copyright &y& Elsevier]

Construction of dye-sensitized solid-state solar cells requires identification of hole collectors and understanding of the dissipative processes that limit the energy conversion efficiency. One of the hole collectors fairly well studied and giving a reasonably high efficiency is CuI. In this note we show that stoichiometrically excess iodine molecules adsorbed at the CuI surface acts as hole trapping sites (located at∼0.2 eV above the conduction band edge) that mediate recombination, affecting the performance of the cell. Fluorescence measurements reveal that exposure of CuI films to iodine vapor generates surface traps and as iodine diffuses to the bulk, surface trap density is greatly reduced. Methods by which the recombination originating from this effect may be circumvented are also discussed. [Copyright &y& Elsevier]

A series of 100 nm thick InGaN films with Indium content up to 14% has been grown by MOVPE on SiC substrates. Cathodoluminescence (CL) and remote electron beam induced current (REBIC) in the scanning electron microscope have been applied to investigate with high spatial resolution the recombination of carriers at the structural defects present in the films. The observed defects are mainly pinholes formed at the surface. The density of pinholes increases with the In content in the layers, which can be explained by elastic relaxation at pinholes. CL images show the spatial distribution of the emission sites. For pinholes with diameter in the μm range we observe enhanced luminescence around the pinhole and a reduced luminescence at the apex. Pinholes are observed in REBIC images as dark spots occasionally surrounded by a bright halo. The halo spreads over an area larger than the pinhole, with a diameter of about 3–4 μm. Also a cell-like dislocation structure has been observed in some samples in the CL and REBIC images. CL spectra show, as common features of the samples, a complex emission in the blue range and a broad structured band centered around 670 nm. The influence of the inhomogeneous Indium incorporation on the luminescence of the films and of charged defects on the observed REBIC contrast is discussed. [Copyright &y& Elsevier]

• PMMA buffer layer is used for the light absorption layer/HTL interface in CsPbI 3 quantum dot solar cells. • Interface carrier recombination is suppressed, and the improvement of V OC and PCE is obtained with PMMA buffer layer. • The stability of QDPSCs with PMMA is significantly enhanced due to the intrinsic hydrophobic characteristic of PMMA. All-inorganic CsPbI 3 quantum dots perovskite solar cells (QDPSCs) have wide potential application due to their excellent photoelectric properties with high environmental stability. However, the poor interface contact between the light absorption layer and hole transport layer (HTL) results in the serious carrier recombination and the large open-circuit voltage (V OC) loss. Herein, we introduce the insulating PMMA (poly(methyl methacrylate)) buffer layer into CsPbI 3 quantum dots (QDs)/Cu 12 Sb 4 S 13 QDs HTL interface in all-inorganic QDPSCs with the structure of FTO/c-TiO 2 /m-TiO 2 /CsPbI 3 QDs/Cu 12 Sb 4 S 13 QDs/Au. The interface carrier recombination is obviously suppressed and the significant V OC improvement from 1.04 V to 1.14 V is obtained with the incorporated PMMA buffer layer. The devices with PMMA buffer layer show the enhanced power conversion efficiency (PCE) of 10.99%, and the improvement of 9.71% is achieved compared to that of the control devices (10.02%). The stability is significantly enhanced due to the intrinsic hydrophobic characteristic of PMMA, and the devices retain 62.69% of their initial PCE after stored in air condition for 15 days, which is greatly improved compared with the control device without PMMA. [ABSTRACT FROM AUTHOR]

Proposed mechanism of photocatalytic H 2 evolution of C 3 N 4 /CoP x under visible light irradiation. [Display omitted] • C 3 N 4 nanosheets are pre-functionalized with L-cysteine molecules. • CoP x NPs are photodeposited on pre-functionalized C 3 N 4 nanosheets. • L-cysteine molecules act as bridging ligands between C 3 N 4 and CoP x NPs. • The optimal hydrogen evolution rate of 4.12 mmolg−1h−1 is obtained. Serious interface carrier recombination leads to moderated photocatalytic performance of carbon nitride (C 3 N 4), and the realization of their strongly covalent bonding with co-catalysts can efficiently inhibit this. In this article, C 3 N 4 nanosheets are first functionalized with L-cysteine molecules to form C-SH bonds, and then the photodeposited CoP x NPs are covalently bonded with C 3 N 4 with L-cysteine molecules as bridging ligands, which can efficiently reduce the C 3 N 4 /CoP x interface impedance. Their optimal hydrogen evolution rate and apparent quantum efficiency at 420 nm are 4.12 mmolg−1h−1 and 3.74%, respectively, which are 17.2 and 13.9 times that C 3 N 4 /CoP x reference without L-cysteine bridging ligands, mainly due to the reduced C 3 N 4 /CoP x interface impedance. This work proposes a general solution to inhibit interface carrier recombination in nanocomposites by introduction of bridging ligands. [ABSTRACT FROM AUTHOR]

The improvement in current density–voltage characteristics and external quantum efficiency of organic photovoltaics with non-toxic polyethylenimine ethoxylated (PEIE) as a modified layer between the electron transport layer and the active layer were demonstrated. The mechanisms of carrier transport, photon generation current, and the carrier recombination influenced by the PEIE layer were systematically studied. An extra PEIE layer was demonstrated having a shorter relaxation time via pump-probe spectroscopy, which provides better charge transfer ability. From capacitance-voltage measurement, the effective capacitance of the device increase with an addition PEIE layer, corresponding to the increase of accumulation carriers generated at the interfaces. Furthermore, electrochemical impedance spectroscopy elucidated that the PEIE layer can reduce the carrier recombination probability in the devices. As a result, the lifetime of the devices with a PEIE layer is improved as compared to the devices without PEIE layer. [Display omitted] • A non-toxic PEIE layer was demonstrated as having a shorter carrier relaxation time via pump-probe spectroscopy, which provides better charge transfer ability in OPV. •The non-toxic PEIE layer not only provides larger effective capacitance of the device resulting from amount of accumulation carriers generated at the interfaces, but also reduces the carrier recombination probability. •The stability of the devices with a PEIE layer is also improved as the device performance can keep within 90 % compared to its original PCE values after 1400-h measurement in a nitrogen-filled glove box without encapsulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient PPPDE interlayer is inserted for the first time in the ETL-free PSCs. • The champion device yields an extraordinary PCE of up to 19.71%. • Ameliorated hysteresis and stability are achieved in PPPDE-based ETL-free PSCs. Organic-inorganic halide perovskites have become promising materials for the next generation of photovoltaic devices on account of the preeminent optoelectronic characteristics and boundless potentialities. Perovskite solar cells (PSCs) normally require a complex structure design with an electron transport layer (ETL) to provide a built-in electric field and depress the probability of carrier recombination. Nonetheless, the construction of a proper ETL is not cost-effective, which precludes the practical commercialization of the PSCs. In this respect, a simplified ETL-free PSC is successfully fabricated by inserting a facile and efficient 1-[N-(2-Hydroxyethyl)-4′-piperidyl]-3-(4′-piperidyl) propane (PPPDE) small-molecule thin interlayer between the FTO substrate and perovskite film. Compared with the bare FTO-based PSCs, this surface engineering can prominently ameliorate the photovoltaic performance parameters, yielding an extraordinary PCE of up to 19.71% with a ca. 31% efficiency enhancement, which can be attributed to the optimized interface energy-level alignment with a barrier-free contact, the elevated charge transfer and collection as well as the suppressed electron-holes recombination at the FTO/perovskite interface. Synchronously, the long-term air stability is also improved with mitigated J – V hysteretic behavior due to the larger grain size of perovskite and the suppressed defect-induced degradation. Furthermore, an augmented performance of 15.87% was achieved for the flexible PPPDE embedded ETL-free PSC fabricated on ITO/PEN substrates via a low-temperature deposition process. The demonstrated PPPDE interlayer presents a brand-new strategy that can simplify the cell configuration and improve the photovoltaic performance of ETL-free PSCs. [ABSTRACT FROM AUTHOR]

Ultrathin Cu(InGa)Se 2 (CIGS) material has become one of the emerging material in the research of solar cell fields due to its excellent optical, electrical and tunable bandgap properties. In this study, we have described a numerical simulation of ultrathin CIGS solar cell using SCAPS-1D program tool based on WS 2 as a buffer layer, CIGS as an absorber layer with a-Si/MoTe 2 as a hole transport layer (HTL). The proposed study also reveals that a-Si is better choice for HTL as compared to MoTe 2 for CIGS solar cell. The cell parameters such as thickness, defect density and acceptor concentration of CIGS absorber layer have been optimized in proposed work. Based on optimization, the maximum power conversion efficiency (PCE) of 30.17% ( V oc =1.093Volts, J sc =32.41 mA/cm2 and FF =85.12%) has been reached for CIGS solar cell with a-Si HTL. The simulation further analyzed at various operating temperature and series resistance for better understanding of the solar device. All these simulation provide noteworthy manifestation for the fabrication of high efficient ultrathin energy harvesting application. • Effect of the CIGS layer thickness on the performance parameter of CIGS solar cell with MoTe 2 , a-Si HTL and without HTL. • Optimization of thickness, doping concentration and defect density of CIGS absorber layer. • Design a cost-effective and non-toxic CIGS solar cell. • Performance analysis at various operating temperature and series resistance. [ABSTRACT FROM AUTHOR]

Motivated by possible application of InGaN/GaN multi-quantum well solar cells in hybrid concentrated photovoltaic / solar thermal power conversion systems, we have analyzed the temperature and intensity dependence of the open-circuit voltage of such devices up to 725 K and more than 1000 suns. We show that the simple ABC model routinely used to analyze the measured quantum efficiency data of InGaN/GaN LEDs can accurately reproduce the temperature and intensity dependence of the measured open-circuit voltage if a temperature-dependent Shockley–Read–Hall lifetime is used and device heating is taken into account. • Open-circuit voltage of InGaN quantum-well solar cells is well described by recombination models. • Temperature dependence is captured by a temperature dependent Shockley–Read–Hall model. • Self-heating becomes relevant at high solar concentration. • A transition to a radiatively limited regime is predicted below 200 K. [ABSTRACT FROM AUTHOR]

A series of Z-scheme In 2 S 3 /BiOBr heterojunctions were synthesized through a two-step hydrothermal method. The results showed that the optoelectronic dynamics of carrier separation efficiency, charge transport and electron/hole recombination rate were improved greatly. As a result, the photocatalytic activity of In 2 S 3 /BiOBr heterojunctions was greatly enhanced under visible-light irradiation. This work will provide a better insight into the formation mechanism BiOBr-based Z-scheme heterojunctions with high photocatalytic performance. [Display omitted] • Z-scheme In 2 S 3 /BiOBr heterojunctions were prepared by a two-step hydrothermal method. • The optoelectronic dynamics was tuned to an optimal domain through changing the contents of In 2 S 3. • The photocatalytic activity of Z-scheme In 2 S 3 /BiOBr heterojunctions was greatly enhanced under visible-light irradiation. • Z-scheme In 2 S 3 /BiOBr heterojunctions demonstrated a high photocatalytic stability in 4 runs. Heterojunction photocatalysts with intimate contact are very promising for organics photodegradation due to their high efficiency in enhancing the light absorption, inhibiting the carrier recombination and improving the photogenerated electron/hole separation. In this study, we demonstrated a two-step hydrothermal method to construct indium sulfide/bismuth oxybromide (In 2 S 3 /BiOBr) heterojunctions for the first time. Importantly, the optoelectronic dynamics of carrier separation efficiency, charge transport and electron/hole recombination rate were tuned to an optimal domain through a series of experiments. As a result, the photocatalytic activity of In 2 S 3 /BiOBr heterojunctions was greatly enhanced under visible-light irradiation. The as-synthesized IS/BOB-0.2 heterojunctions exhibited the highest photocatalytic ability, which was approximately 4.75 times and 11.26 times higher than that of pure BiOBr and TiO 2 P25 catalysts. This work will provide a better insight into the formation mechanism BiOBr-based Z-scheme heterojunctions with high photocatalytic performance. [ABSTRACT FROM AUTHOR]

Organic-inorganic halide perovskites have attracted much attention thanks to their excellent optoelectronic performances. Here, a bulk CH3NH3PbBr3 (MAPbBr3) single crystal (SC) was fabricated, whose temperature and light polarization dependence was investigated by measuring photoluminescence. The presence of obvious band tail states was unveiled when the applied temperature was reduced from room temperature to 78 K. Temperature dependence of the bandgap of the MAPbBr3 SC was found to be abnormal compared with those of traditional semiconductors due to the presence of instabilization of out-of-phase tail states. The MAPbBr3 SC revealed an anisotropy light absorption for linearly polarized light with an anisotropy ratio of 1.45, and a circular dichroism ratio of up to 9% was discovered due to the spin-orbit coupling in the band tail states, exhibiting great polarization sensitivity of the MAPbBr3 SC for the application of light sensors. These key findings shed light on the development of potential optoelectronic and spintronic applications based on large-scaled organic-inorganic perovskite SCs. [ABSTRACT FROM AUTHOR]

Antimony sulphide (Sb 2 S 3) thin films have attracted considerable research interest as a photovoltaic absorber material owing to their suitable band gap, large absorption coefficient, and excellent photoelectronic properties. In this study, cadmium sulphide (CdS) films were doped with potassium, which increased their crystallinity and optical transmission. These films were then used as a buffer layer to increase the efficiency of Sb 2 S 3 solar cells. Furthermore, the potassium diffused into the Sb 2 S 3 film, which increased their crystallinity and light absorption and decreased its surface roughness. Dual-functional potassium doping helped improve all of the photoelectric parameters of the Sb 2 S 3 solar cells. Specifically, the device efficiency increased from 4.57% to 6.53% (an increase of 42.89%), and a high current density of 15.29 mA cm−2 was achieved. These findings are expected to facilitate the further development of Sb 2 S 3 thin-film solar cells for industrial applications. • Potassium doped CdS films were used as a buffer layer to increase the efficiency of Sb 2 S 3 solar cells. The potassium diffused into the Sb 2 S 3 film, increased their crystallinity and light absorption and decreased its surface roughness. • Dual-functional potassium doping helped improve all of the photoelectric parameters of the Sb 2 S 3 solar cells. • Potassium doping can significantly reduce the carrier recombination in Sb 2 S 3 solar cells. • The device efficiency increased from 4.57% to 6.53% (an increase of 42.89%), and the cells delivered a high current density of 15.29 mA.cm-2 was achieved. • Cadmium sulphide (CdS) films were doped with potassium, which increased their crystallinity and optical transmission. • Doping enhance the separation of photoelectron and hole pairs, the interfacial charge transfer ability improved. [ABSTRACT FROM AUTHOR]

In this paper, study on the whole-domain coupling between electromechanical fields and charge carriers inside a piezoelectric PN junction is conducted in detail by abandoning the traditional depletion layer approximation and the low injection assumption. The barrier region of a PN junction has been fully opened in order that the upheaval change of electric field and carrier concentrations near the interface can be clearly exhibited and the evolution laws of potential barrier configuration with mechanical loadings can be thoroughly observed by taking into account the three basic motion modes of charge carriers (drift, diffusion and recombination). Effect of mechanical loadings on performance of piezoelectric PN junctions is further delineated from those changes induced by loadings, including the increment of electric field, the carrier redistribution modes and the disturbance laws of energy levels. It is found that the interface barrier configuration can only be significantly tuned by such a mechanical loading mode that the majority carriers are driven into the barrier region from the two sides to induce local carrier-inversion, while the carrier-inversion phenomenon is shown to be helpful for tuning the recombination rate of electrons and holes. As for the loaded configuration, the locations should be chosen according to that the mechanical loadings can cause the structure within an appropriate length near the PN interface into deformation to produce suitable tuning effect to the nearby barrier. Obviously, an effective mechanical tuning methodology on the potential barrier nature near a piezoelectric PN interface has been formed naturally. On this foundation, both the barrier configuration and the inner recombination rate of carriers can be expediently designed and controlled to realize the optimal conversion between electron current and hole current. Further analysis on a non-equilibrium piezoelectric PN junction subjected to a forward bias voltage shows the regulated mechanism of mechanical loadings on I–V characteristics of a piezoelectric PN junction as follows: the holes/electrons, passing through the PN interface from the p/n-zone into the n/p-zone in the form of majority-carrier current, enter into the recombination mode with the local electrons/holes, which induces the electrons/holes in the right/left sides to flow toward the central barrier region. Such a process indicates that the mutual conversion mechanism between two majority-carrier currents across the interface is just implemented by recombination of charge carriers near the barrier region. Thus, the regulation laws of mechanical loadings on the I–V characteristics of a piezoelectric PN junction are finally illustrated from tuning the potential barrier configuration near the interface and optimizing the recombination rate of electrons and holes in the barrier region. Obviously, study on this topic possesses referential significance to mechanical tuning the performance of piezoelectric PN junctions and piezotronic devices. ga1 • Barrier region of a piezoelectric PN junction was opened with considering all the three basic motion modes of carriers. • The barrier configuration can be tuned by loadings with majority carriers driven into the central region from two sides. • Regulation mechanism on I-V characteristics was revealed from tuning barrier configuration and recombination rate. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) allow for a significant amount of strain relaxation, which is helpful in GaN systems where a large lattice mismatch needs to be accommodated. InGaN QDs with a large indium composition are intensively investigated for light emitters requiring longer wavelengths. These are especially important for developing high-efficiency white light sources. Understanding the carrier dynamics in this large lattice-mismatched system is essential to improving the radiative efficiency while circumventing high defect density. This work investigates femtosecond carrier and photon dynamics in self-organized In 0.27 Ga 0.73 N/GaN QDs grown by molecular beam epitaxy using transient differential absorption spectroscopy, which measures the differential absorption coefficient (Δα) with and without an optical pump. Due to 3D quantum confinement and the small effective mass of InGaN, the low density of states in the conduction band is easily filled with electrons. In contrast, the GaN barrier region is replete with a high density of electrons due to a large effective mass. This contrast in carrier density creates a unique phenomenon in the dynamics, showing a change in the differential absorption coefficient (Δα) sign from negative to positive with time. The ultrafast microscopic processes indicate that right after the optical pump and first photon absorption, the valence (conduction) band states are depleted (replete) of electrons. This ground-state bleaching process makes Δα negative, and the probe beam is not absorbed. The electrons are then gradually transferred from the GaN barrier into InGaN QDs, which absorb the second photon from the probe beam (excited-state absorption), making Δα positive. The presence of excited-state carriers with a long lifetime is indicative of the enhanced availability of carriers for radiative recombination. This effect also promotes stimulated emission and amplified spontaneous emission, which can be used to develop lasers and superluminescent LEDs, respectively. Measurements with multiple pump powers and temperatures further confirm that the efficacy of InGaN QDs is enhanced by this effective mass contrast and 3D reservoir of carriers from the GaN barrier. This effect can be used to improve the internal quantum efficiency of GaN-based light emitters.

Abstract: We characterize 5.5MeV alpha particles emitted from 241Am with a liquid-phase epitaxially grown InSb crystal detector at operating temperatures ranging from 5 to 104K. The pulse height of the energy peak of alpha particles rapidly decreases at temperatures above 40K. We explain this behavior of the peak channel numbers as a function of temperature using a model of the recombination and trapping of generated electrons and holes. [ABSTRACT FROM AUTHOR]

• Ag substitution greatly improves the performance of CuSbS 2 solar cells. • Single phase Ag-substituted CuSbS 2 film is achieved by spray pyrolysis. • Ag substitution could inhibit Sb 2 S 3 impurities. • The device shows a really stable performance in damp-heating condition. CuSbS 2 has been considered as a promising photovoltaic absorber material, due to its earth abundant and environmentally friendly constituents. However, the electron affinity and similar radius of cations bring heavy atomic disorders in CuSbS 2 film, limiting its photovoltaic performance. Herein, we report an efficient way to reduce disorders by introducing Ag atom into CuSbS 2 crystal structure. The crystal structure and chemical analysis confirm that Ag occupies the Cu position in the as-prepared films by the spray pyrolysis. The absorption spectra combined with photoluminescence measurement indicate that Ag-substituted CuSbS 2 films have fewer recombination centers. The density functional theory calculation result reveals that Ag-substituted CuSbS 2 has a more stable crystal structure, and the formation energy of the primary point defects obviously increases. Therefore, Ag-substituted CuSbS 2 photovoltaic device shows asignificantly improved power conversion efficiency from 0.73% to 2.48%. [ABSTRACT FROM AUTHOR]

Bilayer ternary solar cells are a kind of novel organic photovoltaic device with a triple-component active layer but are different from the ternary bulk heterojunction (BHJ) blend. Two binary BHJs with a common acceptor (or donor) are deposited sequentially in this kind of device. Here, we study the fabrication and optimization of bilayer ternary solar cells using metal phthalocyanine donors and fullerene acceptor. The device power conversion efficiency (PCE) shows a significant dependence on the interface between the two binary BHJs. The interface formed by stacking two BHJs directly demonstrates severe restrictions on the device efficiency. We find that the photovoltaic performance of bilayer ternary cells can be improved by inserting a C60 molecular monolayer between the two binary BHJs. The effect of the C60 interfacial layer on charge transport is analyzed based on their transport characteristics under negative bias. A relationship between the C60 interfacial layer and recombination under illumination is discussed. This work reveals a particular influence due to the interface facing three materials in organic solar cells. [ABSTRACT FROM AUTHOR]

• Sn solubility can be enhanced by laser irradiation in GeSn alloy. • Graded bandgap GeSn structure can be formed by laser processing. • Direct bandgap GeSn is achieved by Sn enhancement from 4% to 14%. • Differential reflectivity signal & EDS confirm indirect-direct transition. • Carrier lifetime of ~25 ns verifies good quality of processed material. Low equilibrium solid solubility of Sn atoms in Ge (less than 1%) leads to limitations in application of this material for IR detectors and emitters. Providing of non-equilibrium conditions by powerful pulsed laser radiation can be successfully applied for enhancement of solubility of impurity atoms in the host material. Here we present laser-induced monotonous redistribution of Sn atoms in Ge, based on the thermogradient effect aiming overcoming equilibrium limitations in the solubility. We applied pulsed nanosecond laser radiation to epitaxial Ge 0.96 Sn 0.04 layer grown on Si substrate to increase Sn atomic concentration up to 14% at the surface layer. As a result, indirect-direct graded bandgap GeSn structure was formed. The TEM/EDS cross-section analysis, X-ray photoelectron spectroscopy, Raman and UV reflection spectra confirmed the increase of Sn atomic content at the surface by order of magnitude. SEM and AFM imaging provided evident microstructure changes, while carrier lifetime changes, determined by differential transmittivity, were not observed, indicating that laser irradiation does not generate defects which reduce electronic quality of the material. [ABSTRACT FROM AUTHOR]

• Metallization pretreatment can suppress the point-defect-related luminescence. • Metal-rich ambient during metallization pretreatment can inhibit V cation in AlGaN. • Carbon-clusters will form during metallization pretreatment. • The luminescence centered at 3.9 eV in AlN originates from (V Al)3− rather than C N. • Dislocations are non-radiative recombination as well as excitons binding centers. AlGaN materials have a great prospect in ultraviolet and deep-ultraviolet optoelectronic devices, while the point-defects impede their applications. In this report, we successfully suppressed the luminescence of V cation -related point-defect in AlGaN materials. AlGaN epilayers were grown on AlN/sapphire template by metal-organic chemical vapor deposition and the mixed metal-organic flows were used to pretreat the surface of AlN/sapphire template. The luminescence intensity of (V cation -complex)2− point-defects was reduced by the pretreatment, demonstrating the favorable suppression effect on the luminescence of (V cation -complex)2− point-defects. The ephemeral metal-rich condition and metal-droplets on the AlN/sapphire template were believed to be partially responsible for the suppression. It also supported the conception that the 3.90 eV luminescence in AlN originated from the V cation -related point-defects rather than the C N point-defects. The surface morphology was investigated and an optimized pretreating time of 60 s was obtained. The carrier recombination mechanism was also studied and the results revealed that dislocations not only could act as non-radiative recombination centers, but also could bind the excitons. [ABSTRACT FROM AUTHOR]

The introduction of selenium in the CdTe solar cells has been responsible for high performance CdTe thin film solar cells in recent years. It is an approach to form CdSe x Te 1-x alloys by the interdiffusion using precursor CdSe layer during the CdTe high-temperature deposition process. Nevertheless, the compositionally gradient CdSe x Te 1-x formed by the diffusion makes it difficult to absorb long-wavelength photons adequately. So close-spaced sublimation deposited CdSe x Te 1-x interlayer was incorporated in the CdTe thin film solar cells. It is found that 600 nm CdSe x Te 1-x absorber is useful to increase long-wavelength photons absorption and extend the long-wavelength QE response. Meanwhile, the synergetic effects of the primary absorber deposition processing on CdTe solar cell performance were investigated. The substrate temperature of CdTe deposition has an obvious impact on the cell efficiency. The much higher substrate temperature can efficiently gain larger grain size, increase the crystal quality and promote the interdiffusion of different semiconductor layers. These improvements can efficiently decrease the carrier recombination to obtain a much higher fill factor and open-circuit voltage. • CdSe x Te 1-x was formed by the interdiffusion or the CSS method. • CdSe buffer extends the spectral response for CdTe cells but causes the weak absorption at long wavelengths. • The significant enhancement in device performance is due to the incorporation of CSS CdSe x Te 1-x. [ABSTRACT FROM AUTHOR]

• Ti3+ & O v defects in TiO 2 -B NWs extend light absorption and inhibit fast charge carrier recombination. • Interfacial charge transfer via direct Z-scheme in R–TiO 2 -B:Cu NW enhances charge separation. • Cu-Cu 2 O-TiO 2 ternary heterojunction promotes electron tunneling via dissociation of charge carriers. • R–TiO 2 -B:Cu NWs photocatalyst provide ample photoexcited e− and h+ for dye degradation reactions. • Superoxide O2− and hydroxyl (OH) radicals produced via reduction/oxidation degrade dye molecules. Hydrothermally synthesized TiO 2 -B single-crystalline NWs were uniformly Cu-decorated via co-precipitation method to grow hybrid TiO 2 -B:Cu–NWs. Starting from commercial TiO 2 NPs, systematic evolution of TiO 2 -B, R–TiO 2 -B and R–TiO 2 -B:Cu NW-structures in steps, identified a gradual narrowing of band gap from 3.23 to 2.20 eV. Generation of Ti3+ and oxygen vacancy (O v) related defect states in TiO 2 lattice facilitates enhancing absorption of visible light and also inhibit faster charge recombination via trapping of photogenerated charge carriers. Cu 2 O nanoparticles intimately attached with TiO 2 NW surface enhance the charge carrier separation via interfacial charge transfer between Cu 2 O and TiO 2 , involving direct Z-scheme mechanism. Further, metallic copper, being present with an intermediate band gap, can promote electron tunneling across Cu-Cu 2 O-TiO 2 ternary hetero-junctions and dissociate more efficiently the photoexcited electrons and holes from individual pairs and make those amply available for dye degradation reactions which proceed more efficiently in spite of the reduced surface area and porosity of the hetero-structured photocatalyst. Strongly reductive electrons (e−) in the CB of Cu 2 O produce highly reactive superoxide radicals (O2−) which dominantly contribute in dye degradation, while hydroxyl radicals (OH) produced via oxidation by holes (h+) in the VB of TiO 2 also degrade the dye molecules in a relatively lesser significance. The R-TiO 2 -B:Cu 0.2 NW catalyst degrades the MO dye very rapidly with a rate constant ~0.41 min−1 and an efficiency of dye degradation ~91%, and the MB dye even faster with a rate constant ~0.54 min−1 and an efficiency of dye degradation of ~96%, during 60 min of visible light exposure, which are significantly high as compared to the data available in the contemporary literature. [ABSTRACT FROM AUTHOR]

Na-doped Cu 2 SnS 3 (CTS) solar cells are fabricated and their carrier recombination is examined. The CTS absorbers on Mo-coated soda-lime glass substrates are grown by the sulfurization of NaF/Cu–SnS 2 (900 nm) precursors. The NaF thickness is varied from 0 to 100 nm to vary the Na content in the resulting CTS absorbers. It is disclosed that the large grain with the uniformity of the material distribution (Cu, Sn, and S) in the Na-doped CTS absorber is obtained. With optimal Na doping (NaF thickness of 60 nm), the open-circuit voltage deficit (V OC, def) is obviously reduced, whereas short-circuit current density deficit (J SC, def) is not varied much. The reduction of V OC, def is attributable to the decrease in the carrier recombination across the device. The conversion efficiency (η) is consequently increased to approximately 4.7%. However, with severe Na doping (NaF thickness of over 75 nm), the V OC, def is clearly increased owing to the increase in the carrier recombination, thereby reducing the η. This is occurs because the Sn 2 S 3 and Na 2 S secondary phases near the surface of the CTS film are formed with the severe Na doping. To further increase the η, the J SC, def is reduced through the decrease in CdS buffer thickness. Ultimately, the 5.1%-efficient CTS solar cell is obtained with the Na-doped CTS absorber prepared with the optimal NaF thickness of 60 nm. Image 1 • Carrier recombination of Na-doped Cu 2 SnS 3 (CTS) solar cells is examined. • Optimal Na doping decreases V OC, def with small change of J SC, def. • Reduction of V OC, def is resulting from decrease in the carrier recombination across device. • 5.1%-efficient CTS solar cell is achieved. [ABSTRACT FROM AUTHOR]