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We have demonstrated that the edge recombination effect exists in full area industrial silicon heterojunction (SHJ) solar cells, which can cause significant short-circuit current density (JSC) loss. The mechanism behind this observation was studied using different SHJ cell structures. We demonstrated further that this JSC loss effect can be suppressed effectively by simply controlling the gap between the edge of the transparent conductive oxide layer and that of the cell. Using this strategy, the average JSC of our state-of-art SHJ solar cells was enhanced by 0.36 mA/cm2, resulting in an average efficiency gain of 0.28% absolute.

Granular particles formed on a CuInSe2 (CIS) thin film surface with alkali-halide RbF post-deposition treatment (RbF-PDT) are found to concentrate preferably on other than smooth (112)-planes present on the CIS film surface. As a consequence, a large number of distinctive pores are selectively formed at relatively rough facets. Although the open circuit voltage and fill factor values of CIS solar cells improve with either RbF-PDT or heat-light soaking (HLS) treatment, the effects of these treatments are distinguishable. The ratio of carrier recombination rates at the interface (Ri) to that in the bulk (Rb), namely, Ri/Rb, decreases with RbF-PDT. HLS treatment performed on RbF-PDT CIS devices leads to a further decrease in the value of Ri/Rb, whereas the value of Ri/Rb of CIS devices fabricated without RbF-PDT increases with HLS treatment. Ternary CIS solar cells grown with RbF-PDT and HLS treatment reproducibly demonstrate enhanced photovoltaic efficiencies.

Possible applications of ZnSe:Cr in optoelectronics are discussed. It is shown that 2+ to 1+ photo-ionization of chromium results in efficient pumping of Cr2+ intrashell emission and in energy up-conversion from green to blue. A distinct difference in efficiency of the energy up-conversion is observed between chromium- and iron-doped ZnSe samples. This difference we relate to a very efficient Auger mechanism of photoluminescence quenching in Fe-doped samples. We further demonstrate an anticorrelation of the intensities of mid-infrared Cr emission and up-converted blue emission of ZnSe.

This article shows that the temperature dependence of minority carrier lifetime in mercury cadmium telluride samples of differing dislocation densities can be accounted well by including the dislocation contribution in addition to the contribution of well known radiative, auger, and Shockley–Read recombination mechanisms. The dislocation contribution to the minority carrier lifetime has been calculated on the basis of a recently proposed model [V. Gopal and S. Gupta, IEEE-ED 50, 1220 (2003)] by treating dislocation as a discontinuity of the lattice.

Multiple-component decays of photoluminescence (PL) in InGaN/GaN quantum wells have been widely reported. However, their physical interpretations have not been well discussed yet. Based on wavelength-dependent and temperature-varying time-resolved PL measurements, the mechanism of carrier transport among different levels of localized states (spatially distributed) in such an indium aggregated structure was proposed for interpreting the early-stage fast decay, delayed slow rise, and extended slow decay of PL intensity. Three samples of the same quantum well geometry but different nominal indium contents, and hence different degrees of indium aggregation and carrier localization, were compared. The process of carrier transport was enhanced with a certain amount of thermal energy for overcoming potential barriers between spatially distributed potential minimums. In samples of higher indium contents, more complicated carrier localization potential structures led to enhanced carrier transport activities. Free ...

Photoluminescence properties of InAs/GaAs1−xSbx quantum dots (QDs) are investigated with respect to the Sb-composition of x = 0, 0.15, and 0.25. The QDs demonstrate a type-II band alignment for x = 0.15 and 0.25. In contrast, with well-defined InAs/GaAs QDs, the InAs/GaAs1−xSbx QDs exhibit overlapping spectral features with increasing laser excitation intensity, which are determined to be the result of different carrier recombination routes, including both type-I and type-II pathways. Our investigation indicates that the optical behavior and the carrier dynamics in these InAs/GaAs1−xSbx QDs are much more complicated than in the InAs/GaAs QD counterparts. It provides very useful information for understanding the band structure and carrier dynamics of type-II InAs/GaAs1−xSbx QDs.

The photoluminescence (PL) measurement is considered to be a powerful and convenient method to determine the internal quantum efficiency (IQE) of InGaN/GaN multi-quantum-wells. However, as different calculation models are developed for different PL experiments, the calculated IQE values can sometimes differ a lot, mainly due to different experimental conditions. In this paper, a comparative study is presented among the temperature-dependent PL (TDPL) measurement and power-dependent PL (PDPL) measurement and time-resolved PL (TRPL) measurement, and the relationship between different IQE calculation models is analyzed both theoretically and experimentally. It is revealed that despite distinct IQE values, different PL methods are actually compatible with each other. The discrepancy in TDPL and TRPL results comes from the temperature dependent relationship between the carrier concentration and carrier generation rate. Through a careful conversion of the excitation condition, both TDPL and TRPL results are cor...

The effect of ZnO electron-transporting layers from different processing methods on device performance as well as on stability was investigated. Although inverted devices incorporating a ZnO layer via a sol–gel method or single-solution processing method achieved comparable power conversion efficiency, the former device exhibited better long-term stability than the latter device. The reason for such a phenomenon was traced to oxygen-deficient defects, which affected the long-term stability of inverted devices by altering the resistance of the ZnO layer to oxygen intrusion and influenced the recombination state after long-term storage.

The photoluminescence excitation (PLE) spectra of CuInS2 crystals grown by the traveling heater method (THM) and the iodine vapor transport method (IT) have been examined. THM crystals show significant structure with many peaks and dips in the PLE spectra, whereas IT crystals exhibits two clear peaks at two free exciton energies in the spectrum. The peak and dip structures of PLE spectra at the free exciton energy depend on the monitoring PL peak, the kind of crystals, and temperatures. A proposed relaxation process of excited electron–hole pairs explains peak and dip structures of PLE spectra at the free exciton energies.

Fil: Rubinelli, Francisco Alberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Desarrollo Tecnologico para la Industria Quimica. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnologico para la Industria Quimica; Argentina

Recent experiments indicated an anomalous dependence of carrier lifetime on injection level and of photoconductance on carrier photogeneration rate. In this work mechanisms for these phenomena are proposed which are based on the effects of anomalous increase of carrier lifetime and filling of the defect level by minority carriers, respectively. Distinct from previously known mechanisms, which considered two types of deep defects, traps and recombination centers, our mechanism may take place in semiconductors containing only one type of deep defect, which is a recombination center. It was shown that the anomalous injection-level dependence of lifetime occurs only when the semiconductor is exactly compensated by recombination centers. This conclusion differs from that of the previous model, which concluded that carrier trapping is responsible for the earlier phenomenon. It is shown that the injection-level dependence of carrier lifetime can be used as an experimental tool to determine the deep defect concentration.

We present a theory of the low-frequency noise gain gn and photocurrent gain gp in quantum well infrared photodetectors (QWIPs). Expressions for gn and gp in terms of QW capture probability pc and number of QWs N are obtained. These expressions are valid for any number of QWs N>=1 and capture probability 01) to 1 (for pc-->0). QWIP is well described by a conventional photoconductor theory in the case of low capture probability pc-->1, which corresponds to practical QWIPs. The assumptions of the model are discussed in detail, and a comparison with previously published results is made.

Computer simulation is used to study the effect of iodide impurity on silver cluster formation on AgBr microcrystals. The simulation is based on a nucleation-and-growth model of silver cluster formation in competition with recombination of electrons and holes. The efficiency of silver cluster formation is calculated as a function of microcrystal size and shown to increase with size for the impurity-free control, contrary to experimental data. This behavior is due to a partitioning of the hole between free and trapped states which favors the free side as size increases. As a result, recombination decreases and efficiency increases at large microcrystal size. Iodide impurity decreases efficiency relatively more at larger sizes because it introduces an internal recombination pathway not present in the control simulation. Because of their larger volume-to-surface-area ratios, the larger microcrystals are affected more by this additional recombination pathway than smaller microcrystals.

Several possible doping effects in organic electroluminescent devices are studied within the framework of the trap-charge limited conduction models. A significant increase in the trapped charges in the doped layer can cause an overall trap charge redistribution and a shift of the location of the recombination zone. Some experimental data are analyzed and their possible relevance to our predictions is discussed. An experimental verification scheme is also proposed.

We have developed a numerical model to simulate the double-carrier injection trap-charge limited (TCL) transport processes in organic electroluminescent devices (OEDs). Current–voltage characteristics, energy and charge profiles are obtained and analyzed to understand the mechanisms governing the OED performance under TCL conditions. Good agreement with general experimental trends and previous analytical predictions are achieved. Dependencies on several important parameters (carrier injection level, device thickness, recombination constant, temperature, etc.) are also studied.

Electroluminescence of strained Si0.80Ge0.20/Si(001) pin diodes has been investigated experimentally and by quantitative modeling. The key aspect of this investigation was that by selective epitaxial growth the experimental critical thickness for plastic relaxation (80 nm at Tepi=700 °C and large areas) could be increased in finite pads. SiGe layers with thickness of 60, 72 or 370 nm have been grown within the intrinsic i region of pin structures. Samples free of misfit dislocations revealed electroluminescence with the SiGe no-phonon peak and its transversal optical–phonon replica corresponding to interband transitions. It was found that by increasing the thickness of the SiGe layer the drop in the electroluminescence with increasing temperature could be shifted to higher temperature, so that for the 370 nm thick SiGe sample the emission was observed to persist still at 300 K. Modeling based on drift-diffusion and carrier recombination equations was used to simulate the current–voltage characteristics of...

Over the last few years, tremendous progress has been made in the research field of perovskite solar cells. Not only are record power conversion efficiencies now exceeding 20%, but our understanding about the different mechanisms leading to this extraordinary performance has improved phenomenally. The aim of this special issue is to review the current state-of-the-art understanding of perovskite solar cells. Most of the presented articles are research updates giving a succinct overview over different aspects concerning perovskite solar cells. published

Recently, the extremely large magnetoresistance observed in transition metal telluride, like WTe$_2$, attracted much attention because of the potential applications in magnetic sensor. Here we report the observation of extremely large magnetoresistance as 3.0$\times$10$^4$ % measured at 2 K and 9 T magnetic field aligned along [001]-ZrSiS. The significant magnetoresistance change (~1.4$\times$10$^4$ %) can be obtained when the magnetic field is titled from [001] to [011]-ZrSiS. These abnormal magnetoresistance behaviors in ZrSiS can be understood by electron-hole compensation and the open orbital of Fermi surface. Because of these superior MR properties, ZrSiS may be used in the novel magnetic sensors., Comment: 18 pages, 5 figures, 21 references

We show that the incorporation of a Ga1−xMnxAs layer with x=1% in the intrinsic region of a p–i–n diode produces an intense electroluminescence signal due to electronic transitions that involve holes bound to Mn-related states. The intensity of the electroluminescence signal is weakly affected by the temperature over the range of 5–290 K, thus indicating that the Mn-related hole states act as efficient sites for radiative recombination even at room temperature, despite the strong disorder in the Ga1−xMnxAs at relatively high values of x.

We report a lateral oxide-confinement layer for InP-based devices using lattice-matched AlGaAsSb. The confinement-layer-induced excess loss at different widths was extracted after de-embedding the losses due to carrier diffusion, nonradiative recombination, and changes in internal injection efficiency. The results show that AlGaAsSb oxide acts as an excellent confinement layer, and shows no excess loss down to a width of 4 μm.

Temperature-dependent current-voltage measurements are used to determine the dominant recombination path in thin-film heterojunction solar cells based on a variety of Cu(In,Ga)(Se,S)2 alloys. The activation energy of recombination follows the band gap energy of the respective Cu(In,Ga)(Se,S)2 alloy as long as the films are grown with a Cu-poor final composition. Thus, electronic loss in these devices is dominated by bulk recombination. In contrast, all devices based on absorber alloys with a Cu-rich composition prior to heterojunction formation are dominated by recombination at the heterointerface, with activation energies smaller than the band gap energy of the absorber material. These activation energies are independent from the S/Se ratio but increase with increasing Ga/In ratio.

We present theoretical evidence for the creation of an electron–hole pair at an edge-sharing SiO4 site that is supposed to exist in a-SiO2 as an intrinsic structural defect. The present electron–hole pair consists of a nonbridging oxygen hole center and an E′ center, but these paramagnetic defects do not form a close pair but are separately located by over ∼4 A. The subsequent decay mechanism along with the related radiolytic process is also discussed.

Operation of InGaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with quaternary AlInGaN barriers at room and elevated temperatures is reported. The devices outperform conventional GaN/InGaN MQW LEDs, especially at high pump currents. From the measurements of quantum efficiency and total emitted power under dc and pulsed pumping, we show the emission mechanism for quaternary barrier MQWs to be predominantly linked to band-to-band transitions. This is in contrast to localized state emission observed for conventional InGaN/InGaN and GaN/InGaN LEDs. The band-to-band recombination with an increased quantum-well depth improves the high-current performance of the quaternary barrier MQW LEDs, making them attractive for high-power solid-state lighting applications.

Conventionally, wafers are passivated by thermal oxidation at temperatures exceeding 900 °C for about an hour prior to effective minority carrier recombination lifetime measurement. This article discusses a method where a reduced duration and low-temperature (650 °C) oxidation followed by ultraviolet radiation was found to be efficacious in passivating silicon wafers for photoconductive decay measurements. The effective minority carrier recombination lifetimes of wafers deliberately contaminated with iron, measured by the conventional and the present methods were well correlated.

Long-lasting phosphorescence is observed in Ce3+-doped Ca2Al2SiO7 (CASM) and CaYAl3O7 (CYAM) crystals at room temperature. UV irradiation at 365 nm produces broadband emissions with peaks at 417 nm for CASM and 425 nm for CYAM, which persist for not less than 1 h after the removal of the irradiating light. Based on the time dependence of the intensity of the phosphorescence, the long-lasting phosphorescence in these crystals is considered to be due to the electron–hole recombination at shallow traps, which occurs by a thermally activated process.

We have fabricated a GaAs device containing independently contacted electron and hole layers with a separation of 14 nm. The device processing avoids the use of self-aligned contacts and is, therefore, greatly simplified. Only basic processing facilities are required, and leakage problems typical of self-aligned contacts are prevented. The resulting increased device yield overcomes a technological barrier, which has so far limited the experimental research of the system.

We have derived a closed-form analytical expression for intensity-modulated photovoltage spectroscopic (IMVS) responses of organic bulk-heterojunction (BHJ) solar cells. With the expression, we have predicted the features of the IMVS spectra, extracted physical parameters from the IMVS measurements, quantified the recombination characteristics of the BHJ devices, and compared the IMVS with the transient photovoltage responses. The analytical model has enabled the utilization of the quantitative information that is inherent in the IMVS measurements.

The exciton lifetime has been found to be repeatedly tuned by a MHz frequency acoustic driving without degradation of the optical properties of CdS crystals. The increase in the lifetime, up to 5%, followed by its ∼20% decrease has been detected with increasing driving amplitude. The lifetime increase can now be understood as due to reduction in the electron-hole wave function overlap in electric fields generated by the driving. The decrease in the recombination lifetime is ascribed to a widening of the potential well trapping the exciton due to variations in the local-crystal environment at acoustic driving.

Recombination in single quantum well and multiquantum well InGaN/GaN structures is studied using time-resolved photoluminescence and pulsed photoluminescence measurements. Room-temperature measurements show a rapid lifetime (0.06 ns) for a single quantum well structure, while an increasingly long decay lifetime is measured for multiquantum wells as more quantum wells are incorporated into the structure. Temperature-dependent lifetime measurements show that a nonradiative recombination mechanism activates above 45 K in the single quantum well but is less important in the multiquantum wells.

While sensitization of the photoconductivity, i.e., the increase of the majority carrier lifetime by the addition of recombination centers, is known for many years, there was no evidence or suggestion for the corresponding sensitization of the minority carrier lifetime. In this letter, we present experimental evidence for the existence of such an effect in device quality undoped hydrogenated amorphous silicon films. We propose possible scenarios that can yield the observed effect and mention the possible benefits of the minority carrier sensitization for the improvement of bipolar optoelectronic devices made of this material.

In this letter, we present the results of an experimental study of low-temperature-grown GaAs, which clearly resolves separately both carrier trapping and recombination processes. We extend our previous model to account for the observed carrier dynamics, and show how the material growth and annealing conditions can be adjusted to optimize the material properties for all-optical device applications.

The midgap level in platinum doped n-type silicon, which was proposed to be the dominant recombination center, is identified as a platinum-hydrogen complex. Hydrogenation of the samples is achieved by wet-chemical etching at room temperature. Defect profiles, determined by deep level transient spectroscopy, clearly associate the level with the concentration profile of atomic hydrogen.

The effect of strain on thresholdless Auger recombination in quantum wells has been studied theoretically. A detailed analysis of overlap integrals between the initial and final states of carriers has been carried out. It is shown that the strain affects both qualitatively and quantitatively the overlap integral between the electron and hole states. The Auger recombination coefficient is calculated for InAlAsSb quantum well and its dependence on quantum well parameters, strain, and temperature is analyzed.

We report the measurements of the electron‐hole recombination rate in aqueous CdS colloids on the femtosecond time scale. A fast 2‐ps decay and a slower 45‐ps decay have been observed, and the decay dynamics are found to be very sensitive to the excitation laser intensity. Geminate electron‐hole recombination, responsible for the 45‐ps decay, dominates the decay process at low excitation intensities, while nongeminate recombination, accounting for the 2‐ps decay, becomes more important at high excitation intensities.

When Schottky-contacted Si nanomembranes (SiNMs; 27 nm in thickness) are exposed to light it is mainly the hole transport responding sensitively to the illumination. The electron transport on the contrary remains rather unaffected by the exposure, which cannot be explained by a simple creation of electron-hole pairs. We attribute this effect to the holes activated from SiNM surfaces, which strongly supports the existence of surface doping in SiNMs [P. P. Zhang, E. Tevaarwerk, B. N. Park, D. E. Savage, G. K. Celler, I. Knezevic, P. G. Evans, M. A. Eriksson, and M. G. Lagally, Nature 439, 703–706 (2006)]. Our work suggests that the surfaces play a decisive role when creating and designing optoelectronic devices based on SiNMs.

A low-toxic selenization with post gallium diffusion (PGD) treatment has been demonstrated to increase the bandgap in the surface Cu(In,Ga)Se2 (CIGSe) absorbers and to form double-graded bandgap profiles to improve the cell efficiency. The CIGSe absorber with PGD for 5 min increased open-circuit voltage from 0.49 to 0.66 V and efficiency from 9.2% to 13.2%, contributed by the enhancement of carrier recombination in the space-charge region. The reduction in short-circuit current from 30.8 to 29.9 mA/cm2, attributed to the absorption loss in long-wavelength regions, can be potentially improved by further optimization of the minimum bandgap value in gradient valley.

We have derived the Auger recombination coefficients, as a function of temperature, for In0.4Ga0.6N/GaN self-organized quantum dots from large-signal modulation measurements made on lasers in which the quantum dots form the gain media. The value of Ca = 1.3 ±0.2 × 10−31 cm6 s−1 at room temperature and the coefficient decreases with increase of temperature.

We investigate native point defects in CdS and ZnS, which are conventional n-type buffer layers used in thin-film solar cells. Using hybrid functional calculations, we characterize the electrical behavior of these defects and also consider common impurities such as O, H, and their complexes. We find cation vacancies are the dominant compensating acceptors and recombination centers, and their effects are more dramatic in ZnS than in CdS. We also determine the band alignment for conventional Cu(In,Ga)Se2-based solar cells, giving insight into why CdS outperforms ZnS and why Zn oxysulfides are promising due to their improved conduction band offsets.

The analysis of advanced front-junction solar cells where the metal contact to the base region is locally formed on the back surface in the shape of lines usually requires numerical simulations. Here, we describe an approach based on a geometric formulation of carrier crowding towards the localized contact, in conjunction with a partition of the device in two distinct regions. This permits a one dimensional analysis of carrier flow, both in the region immediately adjacent to the contact and in the peripheral region surrounding it. The resulting model is simple enough to provide insight into the physics of device operation and reasonably accurate in cases of practical interest. By applying it to different cases, we identify unexpected anomalies and explain them in terms of the peculiar interplay between carrier transport and recombination that takes place in this type of solar cell.

Several CuPc/PTCDI-C8 films with different structures (co-deposited, layered, and bilayer) were prepared and their structural properties were studied using X-ray diffraction. In order to study the effects of the active layers' structures on the performance of the device, organic solar cells based on these films were fabricated and their electrical characteristics have been explored. Absorbed prominent diffraction peaks for CuPc/PTCDI-C8 bilayer films indicate the formation of higher degree of crystallinity for this structure compared to the films with layered or co-deposited structures. This crystallinity results in higher device performance due to reduced recombination losses and microscopic shorts within the devices.

We examined the effect of temperature and electric field on the activation energy (Ea) of gate-induced drain leakage (GIDL) of a MOSFET. The measured GIDL current shows a temperature dependence consistent with a non-tunneling mechanism. In the low-electric-field regime and for temperatures above 55 °C, Ea is about 0.4 eV and drops from 0.4 eV to 0.1 eV as the applied gate voltage goes below VFB in the accumulation direction (decreased for the n-channel MOSFET). This suggests that electron-hole-pair generation at Si/SiO2 interface traps (Dit), enhanced by the electric field (the Poole-Frenkel effect), dominates GIDL in that regime. For temperatures below 55 °C, Ea is less than 0.15 eV for both weak and strong electric fields and displays minimal temperature dependence, indicating inelastic trap-assisted tunneling or phonon-assisted tunneling from a trap. In the very strong-electric-field regime (>1 MV/cm), band-to-band tunneling is the dominant mechanism.

The Auger lifetime in crystalline silicon has been measured under high injection conditions using an injection- and temperature-dependent photoconductance apparatus, across a temperature range from 243 to 473 K (−30 to 200 °C). The corresponding ambipolar Auger coefficient was found to have a value of 1.6 × 10−30 cm6/s at 303 K (30 °C) at an injection level of 5 × 1016 cm−3. The Auger coefficient was found to decrease between 243 K and 303 K, and then remain approximately constant up to 473 K. An empirical parameterization of the measured ambipolar Auger coefficient is provided.

Understanding the defect physics of ZnO is crucial in controlling its properties for various applications. We report the observation of an interesting 1.64 eV near-infrared (NIR) photoluminescence from ZnO and its evolution with annealing temperature. Based on a recent calculation on the transition levels of native point defects of ZnO [A. Janotti and C. G. Van de Walle, Phys. Rev. B 76, 165202 (2007)], the NIR emission can be successfully explained by the donor-acceptor transition between VO and VZn and/or the radiative recombination of shallowly trapped electrons with deeply trapped holes at Oi.

formation of delocalized states when the QDs are separated by thick barriers. Our results quantify the improvements in QD uniformity and/or reductions in barrier thickness necessary to create spatially extended states. The results further reveal that identical QDs and delocalized states should not be assumed in realistic models of IBSC device photophysics. We analyze the formation of delocalized states by solv

A silicon surface covered with ∼150 A of strontium titanium oxide was exposed to both atomic and molecular hydrogen at temperatures between 20 and 300 °C. A rf probe was used to continuously monitor changes in charge-carrier recombination centers at the SrTiO3/Si interface by following the steady-state photogenerated carrier concentration in the silicon. Independent passivation of interfacial defects was observed by both atomic and molecular hydrogen.

Research is supported by the State Key Program for Basic Research of China under Grant No. 2011CB302003 and National Natural Science Foundation of China (Nos. 61025020 and 60990312).