Search

Photothermal atomic force microscopy (PT-AFM) enables us to examine non-radiative recombination property with high spatial resolution. In order to realize variable frequency modulation of incident light in PT-AFM, we have proposed a multi-pulse modulation method, where the duration for light illumination is divided into multiple light pulses and their period is varied. We have assessed the validity of the proposed method through acquisition of photothermal signal images on microcrystalline materials under various modulation frequencies.

Colloidal perovskite (cesium lead bromide-iodide) quantum dots (PQDs) with different iodine concentration were prepared. These PQDs show excellent optical properties with high light absorption and high photoluminescence. Light absorption is in the range between 500 and 550 nm and extending into the ultraviolet. The photoluminescence spectra show peaks from 490 to 675 nm. Charge carrier lifetime measurements, obtained with the time-resolved photoluminescence technique, indicate that the dominant mechanisms for recombination are the non-radiative recombination processes. Finally, increasing the iodine content, increases defect concentration in the PQDs.

Colloidal quantum dots (CQDs) are a class of third-generation materials for photovoltaics (PVs) that are promising for enabling high efficiency devices with potential for exceeding the Shockley-Queisser limit. This is due to their potential to decrease thermal dissipation via multiple exciton generation during charge conversion and collection, which could potentially lead to an increase in the photovoltage or photocurrent in colloidal quantum dot photovoltaics (CQD PVs). But despite a predicted upper efficiency limit of 42%–44%, the highest power conversion efficiencies of these PVs using lead sulfide colloidal quantum dots (PbS CQDs) remains at approximately 13% on a laboratory scale. For further improvements, the fundamental recombination mechanisms need to be studied to determine their effects on the open-circuit voltage (VOC) and charge-carrier lifetime as well as the diffusion length of the carriers. Also, surface defect passivation and interface engineering should be studied. In this work, we discuss different pathways for non-radiative recombination losses in lead sulfide colloidal quantum dot photovoltaics (PbS CQD PVs), as well as the strategies for reducing these losses by the passivation of the surface and interface defects. We also discuss routes to overcome limits in the diffusion length of the carriers through the engineering of charge transport layers. This work provides routes for the fabrication of highly efficient CQD PVs.

We report a five-fold luminance increase of green-light-emitting CdSe@ZnS quantum-dot LEDs (QLEDs) in response to treatment with a 2-ethoxyethanol solution of cesium carbonate (Cs2CO3). The maximum luminous yield of Cs2CO3-treated QLED is as high as 3.41 cd A−1 at 6.4 V. To elucidate device-performance improvement, we model measured currents as the sum of radiative and non-radiative recombination components, which are respectively represented by modified Shockley equations. Variations in model parameters show that a shift in Fermi level, reduction of barrier heights, and passivation of mid-gap defect states are the main results of Cs2CO3 treatment. In spite of a large luminance difference, light-extraction efficiency remains the same at 9% regardless of Cs2CO3 treatment because of the similarity in optical structures.

The efficiency potential of chalcopyrite and kesterite solar cells including CIGSe (CuInGaSe2), CIGS (CuInGaS2), CZTS (Cu2ZnSnS4) and CZTSSe [Cu2ZnSn(S,Se )4] solar cells is discussed based on external radiative efficiency (ERE), open-circuit voltage loss, fill factor loss, non-radiative recombination and resistance loss. CIGSe cells achieve efficiency potential of 26.8% and 27.5% by improving the ERE from around 1% to 10% and 20%, respectively. CIGS and CZTS(Se) cells achieve the efficiency potential of 25% and 22%, respectively, by improvement in ERE from around 1 × 10−4% to 3%–5%. The effects of non-radiative recombination and resistance loss upon the properties of wide-bandgap CIGSe, CIGS and CZTS(Se) cells are discussed. In the case of wide-bandgap CIGSe cells, lattice mismatching between the buffer layer and CIGSe active layer and deep-level defects are thought to originate from non-radiative recombination loss. CIGS and CZTS(Se) cells are shown to have lower ERE and higher resistance loss compared to that of CIGSe cells.

In this study, we attempt to identify the presence of surface defects (SDs) at an n-type GaN surface after high-temperature growth and gain insight into their intrinsic features. To this end, first, we carefully investigate n-type GaN samples with different surface etching depths. Low-temperature photoluminescence (PL) spectra reveal that SDs are most likely nitrogen vacancies (VN) and/or VN-related point defects intensively distributed within ∼100 nm from the n-type GaN surface after a high-temperature growth. We investigate the effect of SDs on the internal quantum efficiency (IQE) of green light-emitting diodes (LEDs) by preparing GaInN-based green LEDs employing a surface-etched n-type GaN, which exhibits a prominent enhancement of the PL efficiency with an increase in the etching depth. This effect is attributable to the reduced non-radiative recombination centers in multiple-quantum-well active regions because the SDs near the n-type GaN surface are removed by etching. We discuss strategies of in situ engineering on SDs to further improve the IQE in GaInN-based green LEDs on the basis of the results presented in this study.

The ionic nature of the perovskite material results in a great number of defects in the perovskite film which limits the efficiency and stability of perovskite solar cells. The passivation of the defects can effectively suppress the non-radiative recombination of carriers and improve the photovoltaic performance and stability of perovskite solar cells. In this paper, quinoline is introduced into the perovskite precursor solution. By adjusting the addition amount, it is found that quinoline can effectively induce the growth and orientation of perovskite crystals, consequently, improving the film quality and reduce defect density. The optimized device shows higher VOC (1.142 V) and FF (0.792), and achieved a champion power conversion efficiency of 20.87%. In addition, the hysteresis of the device is suppressed and the stability is improved. The results demonstrate that quinoline is an effective perovskite additive.

The role of a GaAs strain-relaxation interlayer inserted into InGaAs/GaAsP superlattice solar cells was evaluated by measuring the piezoelectric photothermal (PPT) signals in the temperature range from 100 K to a device operation temperature of around 340 K. The PPT signals caused by the non-radiative recombination of electrons photo-excited to the first quantized level were observed. The temperature-dependent PPT signal intensities were assessed using an electron carrier relaxation model comprising four processes: radiative recombination, non-radiative recombination, thermionic emission, and tunneling of carriers through the e2-miniband after thermal excitation from the e1-level. The contribution of holes in the hh1 state was also included in this model, in which e1 and e2 are the first and second electron levels in the conduction band, respectively, and hh1 is the first heavy hole level in the valence band of the quantum wells. A similar analysis was conducted using photoluminescence (PL) spectra to elucidate the carrier transition dynamics in greater detail, because PPT and PL measurements are complementary to each other in terms of non-radiative and radiative electron transitions. Consequently, although the non-radiative recombination remained dominant around room temperature, the quantum yield of the carrier tunneling process increased and became comparable to that of non-radiative recombination. This implies that the recombination loss of the photo-excited carriers is suppressed by the insertion of the GaAs interlayer. By clarifying the role of the inserted interlayer with respect to the non-radiative recombination process, the usefulness of the PPT method is demonstrated.

In this brief review the methods for investigation of charge carrier transport and recombination in thin layers of disordered materials and the obtained results are discussed. The method of charge carrier extraction by linearly increasing voltage (CELIV) is useful for the determination of mobility, bulk conductivity and density of equilibrium charge carriers. The extraction of photogenerated charge carriers (photo-CELIV) allows one to independently investigate relaxation of both the mobility and density of photogenerated charge carriers. The extraction of injected charge carriers (i-CELIV) is effective for the independent investigation of transport peculiarities of both injected holes and electrons in bulk heterojunctions. For the investigation of charge carrier recombination we proposed integral time-of-flight (TOF) and double-injection (DI) current transient methods. The methods allowed us to obtain the following significant results: to determine the reason of the conductivity dependence on electric field strength and temperature in the amorphous and microcrystalline hydrogenated silicon and π-conjugated polymers, the time dependent Langevin recombination, the impact of morphology on charge carrier mobility, the reason of reduced Langevin recombination in RR-PHT (regioregular poly(3-hexylthiophene))/PCBM (1-(3-methoxycarbonyl)propyl-1phenyl-[6,6]-methanofullerene) bulk heterojunction structures – 2D Langevin recombination; and to evaluate that the mobility of holes is predetermined by off-diagonal dispersion in poly-PbO.

Grain interiors (GIs) and grain boundaries (GBs) of perovskites have been investigated using chemically, spatially, and temporally resolved measurements. Two dimensional (2D) chemical mapping measurements revealed the GBs consisted of the non-stoichiometric PbI x or CH 3 NH 3 PbI x , that were characterized by an absence of chloride, an enriched oxygen concentration, and a high density of iodide vacancies. In addition, steady-state 2D photoluminescence showed the bandgap broadening at the GBs while 2D lifetime mapping measurement suggested that the GBs indeed contained deep defect centers. However, it is found that defective GBs in perovskite materials do not act as high recombination sites for photogenerated charge carriers due to the bandgap broadening of non-stoichiometric PbI x or CH 3 NH 3 PbI x perovskites at the GB that forms the potential barriers for photo-generated charge carriers toward the GBs. As a consequence, the photo-generated charge carriers adjacent to the GBs will be easily repelled by the GBs, resulting in a greater reduction of the recombination of photogenerated charge carriers. This is one possible reason for the high performance of CH 3 HN 3 PbI 3-x Cl x based solar cells.

ZnO nano/micro-rods on Zn foil are fabricated through a simple, low-cost, catalyst- and seed-free solvothermal method by using Zn foil as the Zn2+ source and substrate in the sodium hydroxide solution. ZnO nano/micro-rods, which show good crystalline quality and grow along the c-axis, are distributed randomly on the Zn substrate and approximately perpendicular to the Zn substrate. Through analyzing the evolution of peak position and intensity of band gap emission with the temperature, two different non-radiative recombination processes are obtained. At low temperature the main non-radiative process is the thermal effect while at high temperature the main nonradiative process is the thermal escape from the structural defects assisted by LO phonon scattering. The understanding of the non-radiative recombination processes in ZnO nano/micro-rods on Zn foil might provide meaningful information for their potential application in the optoelectronic field.

We investigate the temperature-dependent decay kinetics of type II CdSe-CdTe and CdTe-CdSe core-lateral shell nanoplatelets. From a kinetic analysis of the photoluminescence (PL) decay and a measurement of the temperature dependent quantum yield we deduce the temperature dependence of the non-radiative and radiative lifetimes of hetero nanoplates. In line with the predictions of the giant oscillator strength effect in 2D we observe a strong increase of the radiative lifetime with temperature. This is attributed to an increase of the homogeneous transition linewidth with temperature. Comparing core only and hetero platelets we observe a significant prolongation of the radiative lifetime in type II platelets by two orders in magnitude while the quantum yield is barely affected. In a careful analysis of the PL decay transients we compare different recombination models, including electron hole pairs and exciton decay, being relevant for the applicability of those structures in photonic applications like solar cells or lasers. We conclude that the observed biexponential PL decay behavior in hetero platelets is predominately due to spatially indirect excitons being present at the hetero junction and not ionized e-h pair recombination.

The excitonic recombination dynamics could be mediated by the direct/indirect-to-indirect/direct bandgap transition and the different overlap between electron and hole wave functions caused by polymorph transformation. Here, the direct bandgap zinc-blende semiconductor is unexpectedly observed as an intermediate phase in polymorph transformation from direct bandgap wurtzite to indirect bandgap rock-salt CdS semiconductor nanocrystals. The high-pressure phase of the rock-salt CdS structure has been recovered to the ambient conditions. The radiative recombination lifetimes at the band edge states are 6.167 ns, 8.027 ns and 19.325 ns for the wurtzite, zinc-blende and rock-salt CdS nanocrystals, respectively. The longest radiative recombination lifetime of the indirect bandgap rock-salt CdS semiconductor is probably attributed to the additional requirement for phonon assistance. The increased radiative recombination lifetime of the direct bandgap zinc-blende CdS semiconductor mainly results from the reduced electron–hole wave function overlap. The ability to tune the structure of a nanoscale semiconductor with exquisite precision opens up a new opportunity for mediating the excitonic recombination dynamics within only a single material.

The energy flux in bipolar semiconductors is investigated taking into account the influence of recombination on it. The general expression of an energy flux in a nondegenerate semiconductor is obtained in a linear approximation with respect to perturbation taking into account recombination (the presence of nonequilibrium charge carriers in the semiconductor) and thermal electrical currents of electrons and holes. The energy flux density has been calculated in two different cases, the case of weak recombination and the case of strong recombination, for a one-dimension case.

Perovskite materials are attractive candidates as emitting layers in light-emitting diodes due to their excellent optical and electrical properties. Effective charge radiative recombination is a key to target high-efficiency perovskite light-emitting diodes (PeLEDs). State-of-the-art effective passivation chemicals in PeLEDs mostly belong to organic chelating molecules, associated with like molecular detachment in the device operation, which simultaneously degrades the performance especially the operational stability of the devices. Here, a silane material tetraethoxysilane (TEOS), which can be crosslinkable to avoid any likely detachment from perovskite film, is incorporated into the perovskite film to enhance film radiative recombination and stability. An oxo-bridged silica network anchored with perovskite is formed after the TEOS in-situ crosslinking process. It is found that the lone pair electrons in TEOS network can coordinate with the undercoordinated Pb2+ of perovskite. Consequently, defect states in perovskite film are dramatically diminished, which enhances radiative recombination. The photoluminescence intensity of resultant perovskite-TEOS film is enhanced by 40% over that of the pristine one. The average photoluminescence lifetime of perovskite-TEOS film reaches 58 ns, enhanced by 65% over that of the pristine perovskite film of 35 ns.. As a result, a green PeLED achieved an external quantum efficiency of 16.6% with improved working stability. This work presents a facile strategy targeting efficient and stable perovskite devices via utilizing detachment-free self-crosslinked ligands.

Relationship between the external quantum efficiency (EQE) curves and the dominant non-radiative recombination mechanisms of InGaN green LEDs grown on silicon substrates were investigated. Through the analysis of the ABC+ f ( n ) model, the significant drop in EQE at low current levels is due to an increasingly defect-related Shockley-Read-Hall (SRH) recombination. Under extremely low current densities, the defect traps can even become the dominant channel for the leakage current through the tunneling process, thereby reducing the efficiency of carrier injection into the active region. These observations were further supported by the carrier lifetime measurement. However, this fails to explain the droop in EQE at high current densities, especially when SRH recombination has been saturated. Our results show that carrier leakage has becomes dominant at high current density when Auger recombination has been less impossible. Reduced carrier leakage may lead to increased carrier injection efficiency, which in turn alleviates EQE droop.

Interface engineering is an effective means to enhance the performance of thin‐film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open‐circuit voltage (Voc), short‐circuit current density (Jsc), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35–55% at room temperature. All of these improvements are attributed to the functional PFN‐I layers as they provide favorable interface contact and defect reduction.

For commonly utilized photoluminescence (PL) imaging, the spatial resolution is dictated by the carrier diffusion length rather than by that dictated by the optical system, such as diffraction limit. Here, we show that Raman imaging of the LO phonon-plasmon (LOPP) coupled mode can be used to recover the intrinsic spatial resolution of the optical system, as demonstrated by Raman imaging of defects in GaAs, achieving a 10-fold improvement in resolution. Furthermore, by combining Raman and PL imaging, we can independently determine the spatial profiles of the electron and hole density, radiative and non-radiative recombination rate near a dislocation defect, which has not been possible using other techniques.

We show that increasing the bulk doping in a silicon based solar cell can increase the fraction of photo generated carriers that recombine radiatively at open circuit condition. This increases the maximum achievable open circuit voltage (Voc) in a solar cell At higher doping levels auger recombination and band gap narrowing effects dominate leading to a reduction in Voc. Therefore radiative and non-radiative recombinations at Voc determines the optimum doping of the bulk to maximize the performance especially in thin solar cells with increased surface area due to surface texturing.

We report thin-film InAs/GaAs quantum dot (QD) solar cells with n − i − p + deep junction structure and planar back reflector fabricated by epitaxial lift-off (ELO) of full 3-in wafers. External quantum efficiency measurements demonstrate twofold enhancement of the QD photocurrent in the ELO QD cell compared to the wafer-based QD cell. In the GaAs wavelength range, the ELO QD cell perfectly preserves the current collection efficiency of the baseline single-junction ELO cell. We demonstrate by full-wave optical simulations that integrating a micro-patterned diffraction grating in the ELO cell rearside provides more than tenfold enhancement of the near-infrared light harvesting by QDs. Experimental results are thoroughly discussed with the help of physics-based simulations to single out the impact of QD dynamics and defects on the cell photovoltaic behavior. It is demonstrated that non radiative recombination in the QD stack is the bottleneck for the open circuit voltage ( V oc ) of the reported devices. More important, our theoretical calculations demonstrate that the V oc offset of 0.3 V from the QD ground state identified by Tanabe et al., 2012, from a collection of experimental data of high quality III-V QD solar cells is a reliable – albeit conservative – metric to gauge the attainable V oc and to quantify the scope for improvement by reducing non radiative recombination. Provided that material quality issues are solved, we demonstrate – by transport and rigorous electromagnetic simulations – that light-trapping enhanced thin-film cells with twenty InAs/GaAs QD layers reach efficiency higher than 28% under unconcentrated light, ambient temperature. If photon recycling can be fully exploited, 30% efficiency is deemed to be feasible.

Here, we report the strategies to increase the photon harvesting in single junction organic photovoltaics by band gap engineering. Low band-gap non-fulllerene small molecule acceptors yield remarkable short-circuit current (26.6 mA/cm2) which comparable to existing high efficiency photovoltaic technologies.

Organic solar cells (OSCs) are considered as a promising next-generation photovoltaic technology because of their light weight, flexibility, and the potential of roll-to-roll fabrication. However, the relatively large energy loss (E-loss) from the optical bandgap (E-g) of the absorber to the open-circuit voltage (V-oc) of the device hinders further improvement of the PCEs of OSCs. Here, we report efficient non-fullerene all-small-molecule organic solar cells (NF all-SMOSCs), using DR3TBDTT and O-IDTBR as the donor and acceptor, respectively. We obtain a high electroluminescence yield (EQE(EL)) value of up to approximate to 4 x 10(-4) corresponding to a 0.21 eV non-radiative recombination loss, which is the smallest value for bulk-heterojunction (BHJ) OSCs so far. As a result, a low E-loss of 0.54 eV and a considerably high V-oc of 1.15 V are obtained for BHJ NF all-SMOSCs. Funding Agencies|Japan Science and Technology Agency (JST); Ministry of Education, Culture, Sports, Science and Technology (MEXT) through Center of Innovation (COI) Program; Swedish Energy Agency (Energimyndigheten) [2016-010174]

Solar cells based on organic–inorganic halide perovskites are now leading the photovoltaic technologies because of their high power conversion efficiency. Recently, there have been debates on the microstructure-related defects in metal halide perovskites (grain size, grain boundaries, etc.) and a widespread view is that large grains are a prerequisite to suppress nonradiative recombination and improve photovoltaic performance, although opinions against it also exist. Herein, we employ blends of methylammonium lead iodide perovskites with an insulating polymer (polyvinylpyrrolidone) that offer the possibility to tune the grain size in order to obtain a fundamental understanding of the photoresponse at the microscopic level. We provide, for the first time, spatially resolved details of the microstructures in such blend systems via Raman mapping, light beam-induced current imaging, and conductive atomic force microscopy. Although the polymer blend systems systematically alter the morphology by creating small grains (more grain boundaries), they reduce nonradiative recombination within the film and enhance its spatial homogeneity of radiative recombination. We attribute this to a reduction in the density of bulk trap states, as evidenced by an order of magnitude higher photoluminescence intensity and a significantly higher open-circuit voltage when the polymer is incorporated into the perovskite films. The solar cells employing blend systems also show nearly hysteresis-free power conversion efficiency ∼17.5%, as well as a remarkable shelf-life stability over 100 days.

The non-radiative recombination properties of Cu(In,Ga)Se2 [CIGS] solar cells were investigated locally through photothermal [PT] measurements by atomic force microscopy under various kinds of incident light with photon energies above or below the bandgap of CIGS. We found that the intensity and spatial distribution of the PT signal strongly depended on the photon energy of the incident light and on the Ga content of the CIGS layer. These results suggest the possibilities that photo-generated free electrons could accumulate near the grain boundary because of the built-in electric field and that sub-gap states with discrete energy levels are present in the CIGS material.

En este trabajo, reportamos la caracterización de monocristales de Si(100) y GaSb(111) utilizando espectroscopia Raman y fotoacústica (principal interés) en configuración abierta y cerrada, para compuestos semiconductores III-V con estructura tipo zinc blenda, los espectros Raman generalmente muestran dos picos, un pico a baja frecuencia correspondiente a modos fononicos TO y un pico en alta frecuencia correspondiente a modos fononicos LO. Un fuerte pico es mostrado en la posición 226 cm−1 y uno un poco más débil en 237 cm−1, que son los modos TO y LO respectivamente, debido a la orientación cristalina del material. Con el fin de determinar la difusividad térmica de los materiales se utilizaron láseres con longitudes de onda de 650 nm y 535 nm. Los resultados de la difusividad térmica de los monocristales de Si y GaSb, obtenidos a partir del modelo de Rosencwaig y Gersho (RG) se analizaron en función de la orientación cristalográfica. Discutimos la recombinación no-radiativa que se origina en la superficie y en el volumen del cristal, que contribuye a la señal fotoacústica, en términos del tipo de celda y de la línea de excitación. In this work, we report the characterization of Si (100) and GaSb (111) single crystals by using Raman spectroscopy and a photoacoustic cell in open and closed configuration. For III-V compound semiconductors of the zinc-blende crystal structure, Raman spectra generally show two peaks. The lower-frequency peak corresponds to TO phonons, and the higher frequency peak corresponds to LO phonons. A strong peak was found at 226 cm−1 and a weak peak at 237 cm−1, which are the TO and LO modes, respectively. Raman spectrum of GaSb (111) show that the integrate intensity of TO mode is greater than LO mode due to disoriented of the single crystal. In order to obtain the thermal diffuivity, the crystals were exciting by means of solid-state lasers of wavelengths of 650 nm and 535 nm, respectively. The results of the thermal diffusivity of single crystals, obtained from the Rosencwaig and Gersho (RG) model were analyzed according to the crystallographic orientation. We have also discussed the contribution of the non-radiative recombination to the photoacustic signal from surface and bulk depending on the type of cell and excitation of the laser line.

Temperature dependence of the lifetime of nonequilibrium charge carriers limited by recombination process in a p-n junction space-charge region has been obtained from current–voltage, capacitance–voltage and thermometric characteristics of GaP p + -n junctions in the temperature range 150–500 K. The results have been refined using the data of the junction relaxation characteristics. Parameters of the carriers' lifetime sensitivity to the temperature and current have been determined. It has been established that the charge carriers recombine predominantly through deep single-level amphoteric-type centres. The depth of the centres makes approx. (E C -1.25 eV). We suppose that the nature of the centres formation is not connected with the junction fabrication technology. It has rather fundamental origin. The results of the present investigation could be used in the development of devices based on wide bandgap semiconductors and particularly high temperature diode sensors.

The move towards lower cost sources of solar silicon has intensi-fied efforts to investigate the possibilities of passivating or reduc-ing the recombination activity caused by deep states associated with transition metals. This is particularly important for the case of the slow diffusing metals early in the periodic sequence which are not removed by conventional gettering. In this paper we examine reactions between hydrogen and transition metals and discuss the possibility of such reactions during cell processing. We analyse the case of hydrogenation of iron in p-type Si and show that FeH can form under non-equilibrium conditions. We consider the electrical activity of the slow diffusing metals Ti, V and Mo, how this is affected in the presence of hydrogen, and the stability of TM-H complexes formed. Finally we discuss recent experiments which indicate that re-siting of some transition metals from the interstitial to substitutional site is possible in the presence of excess vacancies, leading to a reduction in recombination activity.

Plasmonic nano-antennas provide broadband spontaneous emission control by confining light on highly sub-wavelength volumes. We realize a plasmonic patch antenna by positioning a emitter within a ultrathin slab of dielectric limited by an optically thick gold layer and a thin gold patch. A single CdSe/CdS colloidal quantum dot is deterministically located just in the center of the antenna by an original in situ optical lithography protocol [1]. Depending on the dimension of the patch antenna and the emitter orientation, different Purcell factors could be achieved leading to different optical properties. For moderate Purcell factors, patch nanoantennas are plasmonic directive single photon sources. For higher Purcell factors, the spontaneous emission acceleration makes the multiexciton radiative recombination more efficient than Auger non radiative recombination. Emission of photons due to multiexcitons recombination could be observe at very short time scale. Such antennas can be very efficiently excited. Such antenna appear to be extremely bright as their luminescence exceed by more than one order of magnitude the one of single nanocrystals. References: [1] Dousse, A. et al. Controlled light-matter coupling for a single quantum dot embedded in a pillar microcavity using far-field optical lithography. Phys. Rev. Lett. 101, 267404 (2008). [2] C. Belacel, B. Habert, F. Bigourdan, F. Marquier, J-P. Hugonin, S. Michaelis de Vasconcellos, X. Lafosse, L. Coolen, C. Schwob, C. Javaux, B. Dubertret, J-J. Greffet, P. Senellart, A. Maitre, Controlling spontaneous emission with plasmonic optical patch antennas, Nanoletters 13 1516 (2013)

The results of theoretical study of the contribution of recombination processes in additional heating of the surface of monocrystalline silicon during multipulse femtosecond laser processing are presented to discussion. The numerical evaluations are made in regimes of the laser radiation below the ablation threshold, when the microgeometry of the surface is formed due to the processes of self-organization. The influence of Auger recombination processes on the photoexcitation of the semiconductor during the pulse and relaxation after the pulse is studied in detail. It is shown that the additional heating of the surface due to non-radiative recombination is extremely small at pulse repetition rate 10 Hz–1 MHz. Mutual influence of recombination processes of both types is shown.

Summary form only given. Electron-phonon scattering and anharmonicity are the dominant mechanisms, that enable to describe the equilibrium phonon properties in graphene and Raman scattering is the main tool for their characterization. In the first tens fs after the photoexcitation, an out of equilibrium distribution of (hot) electron is induced with respect to the (cold) phonon bath. Within a few picoseconds, the fast electron-electron and electron-phonon non radiative recombination channels determine the equilibrium between the electronic distribution and the lattice. Therefore, on the laboratory timescale, continuous wave laser sources, commonly used for high resolution spontaneous Raman scattering, examine already equilibrated carrier-phonon distributions. A way to impulsively localize energy into graphene's electronic subsystem is provided by sub picosecond photoexcitation. While the behaviour of hot charge carriers to such ultrafast perturbation has been thoroughly elucidated unraveling the nature of optical phonons under a strongly out of equilibrium regime is a challenge. We perform spontaneous Raman measurements in graphene by using a 3-ps laser excitation, which is revealed to be a good agreement between impulsive stimulation and the necessity of spectral resolution. Furthermore, we show how the Raman response of graphene can be detected in presence of an electronic subsystem temperature largely exceeding that of the phonon bath. We find a peculiar behaviour of the period and lifetime of both G and 2D phonons as function of the carriers' temperature in the range 1700-3100 K, which is strongly suggestive of a smearing out of the Dirac cones. We rationalize such behaviour by accordingly revisiting the traditional theoretical modeling of the electron-phonon coupling in this highly excited transient scenario, which is critical in the emerging field of graphene-based nanophotonic and optoelectronic devices operating at THz rates.

This paper proposes a new aging mathematical model for InGaN/GaN-based light-emitting diodes (LEDs) based on non-radiative recombination. Light attenuation is an important index of the performance of LEDs, Arrhenius model as the main aging mathematical model of light attenuation is poorly targeted and cannot reflect the physical significance. Based on the physical theory of deep level defects and non-radiation recombination centers, we analyze the aging mechanism of LED chips and then establish the aging mathematical model. Meanwhile, a batch of GaN-based blue LED chips are selected to conduct accelerated life tests with constant current stresses, and the experimental data is obtained to verify the new model. The result shows that compared with the traditional Arrhenius model, the new model has many advantages such as more accurate, strong pertinence and obvious physical meaning.

Effect of an internal built-in electric field on the non-radiative recombination process of strain-balanced InGaAs/GaAsP multiple quantum wells (MQWs) inserted into a GaAs p–i–n solar cell structure was investigated using the piezoelectric photo–thermal technique. From the experimental data obtained from two types of p–i–n solar cell structures with partly charge-neutral and uniform-gradient potentials, the decrease in the built-in electric field contributed to the decrease in the non-radiative carrier recombination in the MQW. This phenomenon was especially pronounced in the higher photon energy of the incident light and in large quantum well stack number. With the increase in the photon energy, the penetration length shortened, and most carriers were generated in the charge-neutral area in the i-region. The present experimental results could be understood by the increase in the radiative recombination processes within the MQW because of the wave function overlap is essentially unity.

This article reviews the basic physical processes of charge transport and recombination in organic semiconductors. As a workhorse, LEDs based on a single layer of poly(p-phenylene vinylene) (PPV) derivatives are used. The hole transport in these PPV derivatives is governed by trap-free space-charge-limited conduction, with the mobility depending on the electric field and charge-carrier density. These dependencies are generally described in the framework of hopping transport in a Gaussian density of states distribution. The electron transport on the other hand is orders of magnitude lower than the hole transport. The reason is that electron transport is hindered by the presence of a universal electron trap, located at 3.6 eV below vacuum with a typical density of ca. 3 × 10¹⁷ cm⁻³. The trapped electrons recombine with free holes via a non-radiative trap-assisted recombination process, which is a competing loss process with respect to the emissive bimolecular Langevin recombination. The trap-assisted recombination in disordered organic semiconductors is governed by the diffusion of the free carrier (hole) towards the trapped carrier (electron), similar to the Langevin recombination of free carriers where both carriers are mobile. As a result, with the charge-carrier mobilities and amount of trapping centers known from charge-transport measurements, the radiative recombination as well as loss processes in disordered organic semiconductors can be fully predicted. Evidently, future work should focus on the identification and removing of electron traps. This will not only eliminate the non-radiative trap-assisted recombination, but, in addition, will shift the recombination zone towards the center of the device, leading to an efficiency improvement of more than a factor of two in single-layer polymer LEDs.

We study the impact of misfit dislocations on the luminescence from InAs quantum dots (QDs) grown on Si substrates. Electron channeling contrast imaging is used together with cathodoluminescence mapping to locate misfit dislocations and characterize the resulting nonradiative recombination of carriers via near-infrared light emission profiles. With a 5 kV electron beam probe, the dark line defect width due to a typical misfit dislocation in a shallow QD active layer is found to be approximately 1 μm, with a 40%–50% peak emission intensity loss at room temperature. Importantly, we find that at cryogenic temperatures, the dislocations affect the QD ground state and the first excited state emission significantly less than the second excited state emission. At the same time, the dark line defect width, which partially relates to carrier diffusion in the system, is relatively constant across the temperature range of 10 K–300 K. Our results suggest that carrier dynamics in the QD wetting layer control emission intensity loss at dislocations, and that these defects reduce luminescence only at those temperatures where the probability of carriers thermalizing from the dots into the wetting layer becomes significant. We discuss the implications of these findings toward growing dislocation-tolerant, reliable quantum dot lasers on silicon.

Nickel oxide (NiO) would be an alternative hole transport layer for perovskite light-emitting diodes (PeLEDs). However, the performances of NiO-based PeLEDs are still inferior due to the adverse non-radiative recombination at the interface. Here, a poly(9-vinlycarbazole) (PVK) layer is inserted between the perovskite and the NiO film. The photoluminescence quantum yield is dramatically enhanced from 23% to 54% in the presence of PVK layer owing to suppression of the non-radiative recombination. Combined with the favorable hole injection from the ladder energy band scheme of NiO/PVK layer, an external quantum efficiency of 11.2% for a green PeLED is achieved. This work demonstrates the importance of interface control to boost the radiative recombination rate for high performance PeLEDs.