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The ordered alignment of polar organic cations in hybrid organic–inorganic perovskites causes a ferroelectric phase, which is believed to be benign for photovoltaic devices. Using a combination of ...

Nonradiative charge recombination comprises a main pathway for energy losses that impedes the performance of all-inorganic perovskite solar cells. Grain boundaries (GBs) defects are unavoidable in ...

Despite the booming research in organometal halide perovskite solar cells (PSCs) of recent years, considerable roadblocks remain for their large-scale deployment, ranging from undesirable current-voltage hysteresis to inferior device stability. Among various plausible origins of hysteresis, interfacial ferroelectricity is particularly intriguing and warrants a close scrutiny. Here, we examine interfacial ferroelectricity in MAPbI

With the growing demands of renewable energies and environmental protection, photocatalysts attract a lot of attention and are believed to be the most promising approach to harvest solar energy. Th...

Carbonaceous nanolights, carbon dots (CDs), are attractive alternatives to semiconducting quantum dots owing to their tunable optoelectronic properties, photostability, biocompatibility, water solu...

The Shockley-Read-Hall (SRH) model, in which the deep trap defect states in the band gap are proposed as nonradiative electron-hole (e-h) recombination centers, has been widely used to describe the nonradiative e-h recombination through the defects in semiconductor. By using the ab initio nonadiabatic molecular dynamics method, we find that the SRH model fails to describe the e-h recombination behavior for defects in 2D monoelemental material such as monolayer black phosphorus (BP). Through the investigation of three intrinsic defects with shallow and deep defect states in monolayer BP, it is found that, surprisingly, none of these defects significantly accelerates the e-h recombination. Further analysis shows that because monolayer BP is a monoelemental material, the distinct impurity phonon, which often induces fast e-h recombination, is not formed. Moreover, because of the flexibility of 2D material, the defects scatter the phonons present in pristine BP, generating multiple modes with lower frequencies compared with the pristine BP, which further suppresses the e-h recombination. We propose that the conclusion can be extended to other monoelemental 2D materials, which is important guidance for the future design of functional semiconductors.

Defects, such as halide interstitials, act as charge recombination centers, induce degradation of halide perovskites, and create major obstacles to applications of these materials. Alkali metal dopants greatly improve perovskite performance. Using ab initio nonadiabatic molecular dynamics, it is demonstrated that alkalis bring favorable effects. The formation energy of halide interstitials increases by up to a factor of four in the presence of alkali dopants, and therefore, defect concentration decreases. When defects are present, alkali metals strongly bind to them. Halide interstitials introduce mid-gap states that rapidly trap charge carriers. Alkalis eliminate the trap states, helping to maintain high current density. Further to charge trapping, the interstitials accelerate charge recombination. By passivating the interstitials, alkalis make carrier lifetimes up to seven times longer than in defect-free perovskites and up to thirty times longer than in defective perovskites.

Two kinds of CNT@TiO 2 biomimetic composites with needle-leaved (NL) and broad-leaved (BL) trees morphology were synthesized respectively by a simple one-step solvothermal method for the first time. The TiO 2 leaves located on CNT stems act as active sites for photocatalysis. The method allows one to prepare the composites with distinguish morphology of TiO 2 leaves by adjusting the mass ratio of CNT and TiO 2 . In the photodegradation test of methylene orange, the reaction rate up to eightfold increment was observed with both the biomimetic composites compared to bare TiO 2 . The improved photocatalytic activity could be owed to two aspects, namely the enhanced light trapping and scattering ability benefited from large specific area and the direct transport pathway for electrons conducted by CNT, which all derive from the advantages of the unique tree-like structure. This work presents a new strategy to synthesize hetero-photocatalysts with maximized light-harvesting efficiency and low electron hole recombination rate concurrently. These results demonstrate the great potential of biomemic composites and would stimulate further research in photocatalysis and related areas.

In this research, efficiency enhancement of dye-sensitized solar cell (DSSC) with Ag doped TiO2 core-shell (C–S) as plasmonic photoanode structure, abbreviated as Ag@TiO2, was investigated using Sol-Gel- Dr Blade method. Different amount of Ag in two different thick of photoanode were applied to enhance the light absorption for high-performance DSSCs. The localized surface plasmonic resonance (LSPR) effect of Ag@TiO2 showed an improvement in light trapping and power conversion efficiency (PCE) of developed DSSCs. Conforming to the conclusions under AM 1.5 spectrum, the prepared plasmonic solar cells exhibited 21.9% and 41.46% increase in PCE for 13 μm and 8.4 μm thick of photoanode, respectively.

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.

Based on the incorporation of polyoxometalates (POMs) into TiO2 film, the photoelectrochemical performance of POMs/TiO2 anode was elucidated by comparative investigation on the electron transport and electron–hole recombination in POMs/TiO2 anode. The photoelectrochemical performance of the POMs/TiO2 anode was clearly dependent on the type and content of POMs. Compared to the TiO2 anode, the POMs/TiO2 anode with low POMs loadings (0.75%) displayed the enhanced photoelectrochemical performance, while the excessive content (7.5%) of POMs could almost cause a negative effect. Thus, POMs could act as either “shallow electron trap” or “deep electron trap” depending on the different types and contents of POMs. This study reveals that the introduction of POMs into TiO2 anode could facilitate photogenerated electron transfer and reduce electron–hole recombination, which is urgently desired to develop advanced composite materials of POMs/TiO2 for application in photoelectrochemical catalysis and solar cells. Keywords: Polyoxometalates, TiO2, Photoelectrochemical performance, Electron transport, Electron–hole recombination

We apply highly predictive 2-D device simulation to assess the impact of various impurities on the performance of next-generation industrial silicon solar cells. We show that the light-induced boron-oxygen recombination center limits the efficiency to 19.2% on standard Czochralski-grown silicon material. Curing by illumination at elevated temperature is shown to increase the efficiency limit by +1.5% absolute to 20.7%. In the second part of this paper, we examine the impact of the most important metallic impurities on the cell efficiency for p- and n-type cells. It is widely believed that solar cells on n-type silicon are less sensitive to metallic impurities. We show that this statement is not generally valid as it is merely based on the properties of Fe but does not account for the properties of Co, Cr, and Ni.

This paper discusses the exciton dissociation process at the donor–acceptor interface in organic photocells. In our previous study, we introduced a local temperature to handle the hot charge-transfer (CT) state and calculated the exciton dissociation probability based on the 1D organic semiconductor model [T. Shimazaki and T. Nakajima, Phys. Chem. Chem. Phys. 17, 12538 (2015)]. Although the hot CT state plays an essential role in exciton dissociations, the probabilities calculated are not high enough to efficiently separate bound electron–hole pairs. This paper focuses on the dimensional (entropy) effect together with the hot CT state effect and shows that cooperative behavior between both effects can improve the exciton dissociation process. In addition, we discuss cooperative effects with site-disorders and external-electric-fields.

The financial support of the Presidium of the Urals Branch of the Russian Academy of Sciences and of the Ikerbasque Fellowship Foundation, Basque Country, Spain, are greatly acknowledged.

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.

Nitride-based light-emitting diodes (LEDs) suffer from a reduction (droop) of the internal quantum efficiency with increasing injection current. This droop phenomenon is currently the subject of intense research worldwide, as it delays general lighting applications of GaN-based LEDs. Several explanations of the efficiency droop have been proposed in recent years, but none is widely accepted. This feature article provides a snapshot of the present state of droop research, reviews currently discussed droop mechanisms, contextualizes them, and proposes a simple yet unified model for the LED efficiency droop. Illustration of LED efficiency droop (details in Fig. 13).

A series of top-emitting organic light-emitting devices with different thicknesses of carrier transporting layers (N,N′-di(1-naphtyl)-N,N′-diphenylbenzidine, tris(8-hyroxyquinloine) aluminum (Alq 3 )) and emitting layer (EML, 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)-doped Alq 3 ) were fabricated. C545T-doped Alq 3 was found to bring about double recombination peaks in EML. As the distance between EML and reflective anode was increased, the outcoupling efficiency greatly deviated from optically-simulated values due to charge imbalance in EML and optical loss at the EML/Alq 3 interface. The device with 30 nm of EML exhibited maximized outcoupling efficiency and further increase of EML thickness brought about decrease in efficiency due to decrease in hole–electron recombination at the EML/Alq 3 interface.

A physical model describing the dose rate response and the effect of hydrogen in bipolar technologies is presented. The model uses electron-hole pair recombination and competing hydrogen reactions to explain the behaviors of bipolar devices and circuits at different dose rates. Dose-rate-dependent computer simulations based on the model were performed, and the results provide excellent qualitative agreement with the dose rate data taken on both gated lateral pnp bipolar test transistors and LM193 bipolar dual-voltage comparators. The model presented in this paper can be used to explain a variety of factors that can influence device dose rate response in bipolar technologies.

Efficient lighting and display have become important concerns in the energy-starved modern world. This has led to new paradigms in lighting and display technologies. Organic molecules provide a new class of active materials for such technologies. This article gives the basic science behind the design of such molecular materials used in displays and lighting.

Current understanding and control of semiconductor contacts increasingly require measurements sensitive to defects and chemical changes at nanoscale interfaces. We offer examples illustrating dramatic macroscopic effects occurring in semiconductor systems as a result of nanoscale interface phenomena. In some cases, there is interplay of several competing defect-driven mechanisms. Elucidating them and finding the leading ones require careful experimental approach. For single-crystalline ZnO, we study the role of near-surface defects on the formation of Au Schottky contacts. Among the factors degrading the rectifying characteristics of such contacts one should consider the following. High concentrations of shallow donors in the surface and subsurface regions lead to barrier thinning, resulting in increased tunneling. Alternatively, the presence of deep defects near contact interface promotes tunneling by defect-assisted hopping. Nanoscale electronic and chemical studies show that independent reduction of bo...

Composite WO3–TiO2 semiconductor films were cathodically electrodeposited using sequential deposition of WO3 and TiO2 from aqueous baths containing peroxytungstate and titanyl precursor species, respectively. The composite films were prepared by switching the baths for five cycles of deposition at −0.45 V (for WO3) and −0.95 V (for TiO2). These new films were compared and contrasted with composite WO3–TiO2 films prepared by pulsed electrodeposition from a mixed bath. Neat WO3 films were also included for this comparison; the best photoelectrochemical response was shown by the composite films obtained from the new procedure. Keywords: Photoelectrochemical response, Oxide semiconductor, Photoaction spectra, Cathodic electrodeposition

We analyze the influence of the characteristics of the STM-tip (applied voltage, tip radius) on the electroluminescence spectra from an STM-tip-induced quantum dot taking into account the many-body effects. We find that positions of electroluminescence peaks, attributed to the electron-hole recombination in the quantum dot, are very sensitive to the shape and size of the confinement potential as determined by the tip radius and the applied voltage. A critical value of the tip radius is found, at which the luminescence peak positions as a function of the tip radius manifest a transition from decreasing behavior for smaller radii to increasing behavior for larger radii. We find that this critical value of the tip radius is related to the confinement in the lateral and normal direction., Comment: 15 pages, 5 figures

Light-emitting diodes emitting near 2 μm producing quasi-continuous wave optical power of at room temperature have been demonstrated. The combination of a strain-engineered quantum well active region and a cascaded injection scheme made it possible to achieve an internal efficiency of 120%. The higher wall plug efficiency of the two-cascade devices indicates that Auger recombination is primarily responsible for the efficiency drop at high injection levels.

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.

A photoluminescence (PL) study has been performed on a set of p-type bulk single crystalline samples of CdGeAs2. At liquid-helium temperatures, a PL band peaking near 0.55 eV was observed in samples with enhanced absorption at 5.5 μm. This PL band was observed to vary as much as 40 meV in peak position in our sample set. The PL peak position depends on the net acceptor concentration (i.e., hole concentration) and the PL peak shifts to higher energy as the excitation intensity increases. We show that this behavior is well explained by the model of donor–acceptor pair (DAP) recombination in the presence of potential fluctuations.

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.

The possibility of using CdS nanocomposites for optical cooling is analyzed on the basis of their spectroscopic properties. The physical principles of laser cooling in semiconductor structures are discussed.

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 ...

The phenomenon of spatial confinement of the electron-hole recombination in exchange-coupled donor-acceptor pairs was observed by optically detected magnetic resonance in AgBr nanocrystals formed as a result of the self-organized growth in an ionic KBr crystal matrix. The effect is manifested by the maximum distance between recombining donors and acceptors being restricted to the nanocrystal size and by a change in the g value of shallow electron donor centers. Based on an analysis of the exchange interactions, the distribution of distances in the donor-acceptor pairs is determined and the dimensions of nanocrystals are estimated.

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.

Nominally pure BaF 2 single crystals were investigated at 77 v K with optical absorption and electron paramagnetic resonance to understand the mechanism of radiation damage. We find that X-irradiation at 77 v K of undoped BaF 2 produces V k - and F -centres having absorption bands at 3.4 and 2.3 v eV respectively.

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.