Quantum Efficiency Analysis Research Articles

A high-resolution spectroscopic technique for the analysis of the external quantum efficiency of a multimode semiconductor laser

The high-resolution emission spectra of a GaN-based semiconductor laser were utilized to investigate the external differential quantum efficiency variation with temperature and stability over an extended period of continuous operation time. Moreover, the dynamics and evolution of the optical gain and longitudinal modes emitted both below and above threshold current were also reported. Upon studying the L-I curves over the full range of operating current and temperature, three distinct temperature regimes of the quantum efficiency were identified, with the regime of the temperature range 285–301 K yielding the highest stability. The thermal stability of the laser was also assessed by monitoring the variation of threshold current with temperature.

Improved Efficiency in WSe2 Solar Cells Using Amorphous InOx Heterocontacts.

van der Waals (vdW) layered materials have been shown to have excellent optoelectronic properties relevant to photovoltaics. Despite their promise, the demonstrated efficiencies of vdW material solar cells remain low and are seldom supported by statistics or spectral quantum efficiency analysis. In this study, we utilize a p-type WSe2 absorber, forming a solar cell with a transparent front InOx electron contact, and a rear Pd reflector/hole contact. We fabricate multiple devices providing statistics for 10 devices with an average 1 sun conversion efficiency above 5%, among which a champion efficiency of 6.37% is achieved. This is the highest AM 1.5G 1 sun efficiency reported for a vdW material solar cell, with a current density supported by external quantum efficiency analysis. This cell is also shown to have near unity quantum efficiency around λ = 600 nm. This work provides support to vdW materials being considered as serious candidates for future thin-film solar cells.

Behavior analyses of chromium into LiZnNbO4 host through optical spectroscopy and X-ray diffraction

A LiZnNbO4 sample was produced through the solid-state reaction method, according to which, chromium was introduced in the sample as impurity. X-ray diffraction (XRD), luminescence, excitation, emission decay time and emission quantum efficiency analyses were carried out. Structural analysis based on the sample's XRD data showed LiZnNbO4 compound belonging to the P4122 space group. Luminescence measurements evidenced broad emission band centered at 800 nm, which was associated with spin-allowed electronic transition from the excited state 4T2(4F) to the fundamental state 4A2(4F). Emission decay time reached 7.8 μs under 460 nm excitation and 0.43 quantum efficiency. Excitation spectrum showed bands associated with of Cr3+ ions transitions4A2(4F)→ 4T1(4F) and 4A2(4F)→ 4T2(4F), at 460 nm and 644 nm, respectively in octahedral symmetry. Crystal field parameter Dq = 1553 cm−1 and Racah B = 621 cm−1 were found by using transition energies from both the excitation spectrum and Tanabe-Sugano matrices.

Ni(II)-doped CuWO4 photoanodes with enhanced photoelectrocatalytic activity

CuWO4 has emerged in the last years as a ternary metal oxide material for photoanodes application in photoelectrochemical cells, thanks to its relatively narrow band gap, high stability and selectivity toward the oxygen evolution reaction, though largely limited by its poor charge separation efficiency. Aiming at overcoming this limitation, we investigate here the effects that Cu(II) ion substitution has on the photoelectrocatalytic (PEC) performance of copper tungstate. Optically transparent CuWO4 thin-film photoanodes, prepared via spin coating and containing different amounts of Ni(II) ions, were fully characterized via UV–Vis spectroscopy, XRD and SEM analyses, and their PEC performance was tested via linear sweep voltammetry, incident photon to current efficiency and internal quantum efficiency analyses. From tests performed in the presence of a hole scavenger-containing electrolyte, the charge injection and separation efficiencies of the electrodes were also calculated. Pure-phase crystalline and/or heterojunction materials were obtained with higher PEC performance compared to pure CuWO4, mainly due to a significantly enhanced charge separation efficiency in the bulk of the material.Graphic abstract

Highly Efficient Silicon-Based Thin-Film Schottky Barrier Photodetectors

Internal photoemission (IPE) is a promising phenomenon for sub-bandgap photodetection at near-infrared wavelengths using large bandgap semiconductor materials. To improve the photon-to-electron conversion efficiency in silicon-based sub-bandgap Schottky barrier photodetectors (SBPDs), previous studies have mainly focused on subwavelength-scale nanostructures to enhance the electric fields and optical absorption. Here, in a different way from the previous approaches, we theoretically and experimentally demonstrate a rigorous quantum efficiency analysis framework that can quantitatively explain the hot carrier transport processes. Guided by the design principles from the hot carrier loss mechanism analysis, we experimentally demonstrate patternless thin-film SBPDs that can surpass the performance of conventional nanostructured SBPDs, exceeding the external quantum efficiency of 10–3. Our work shows that optical absorption and hot carrier generation are responsible for only a part of the entire IPE process and other transport mechanisms should be carefully considered in a wholistic manner, indicating the importance of quantitative quantum efficiency analysis.

Simulation of Photosynthetic Quantum Efficiency and Energy Distribution Analysis Reveals Differential Drought Response Strategies in Two (Drought-Resistant and -Susceptible) Sugarcane Cultivars

Selections of drought-tolerant cultivars and drought-stress diagnosis are important for sugarcane production under seasonal drought, which becomes a crucial factor causing sugarcane yield reduction. The main objective of this study was to investigate the differential drought-response strategies of drought-resistant ('ROC22') and -susceptible ('ROC16') sugarcane cultivars via photosynthetic quantum efficiency (Φ) simulation and analyze photosystem energy distribution. Five experiments were conducted to measure chlorophyll fluorescence parameters under different photothermal and natural drought conditions. The response model of Φ to photosynthetically active radiation (PAR), temperature (T), and the relative water content of the substrate (rSWC) was established for both cultivars. The results showed that the decreasing rate of Φ was higher at lower temperatures than at higher temperatures, with increasing PAR under well-watered conditions. The drought-stress indexes (εD) of both cultivars increased after rSWC decreased to the critical values of 40% and 29% for 'ROC22' and 'ROC16', respectively, indicating that the photosystem of 'ROC22' reacted more quickly than that of 'ROC16' to water deficit. An earlier response and higher capability of nonphotochemical quenching (NPQ) accompanied the slower and slighter increments of the yield for other energy losses (ΦNO) for 'ROC22' (at day5, with a rSWC of 40%) compared with 'ROC16' (at day3, with a rSWC of 56%), indicating that a rapid decrease in water consumption and an increase in energy dissipation involved in delaying the photosystem injury could contribute to drought tolerance for sugarcane. In addition, the rSWC of 'ROC16' was lower than that of 'ROC22' throughout the drought treatment, suggesting that high water consumption might be adverse to drought tolerance of sugarcane. This model could be applied for drought-tolerance assessment or drought-stress diagnosis for sugarcane cultivars.

Ni3S2 entrenched MWCNT composite as a low-cost Pt-free counter electrode for dye-sensitized solar cell: Conversion efficiency reached to 9.28%

• A simple and cost effective hydrothermal method was adopted to synthesize ultrafine Ni 3 S 2 /MWCNT hybrid CEs. • Ni 3 S 2 /CNT50 composite counter electrode has the maximum Power Conversion Efficiency (PCE) of 10.2 %. • This could be due to the Enhancing the light absorption property in the visible light region and diminish the recombination process. Engineering the surface structure and constructing a suitable internal conductive network is essential for the electron transfer rate and the active materials utilization efficiency of an electrode A novel porous micro-nanostructure based on nickel disulfide (Ni 3 S 2 ) nanoparticles interconnected with carbon nanotubes (CNTs) has been synthesized through a facile hydrothermal method. Shape, quantum states, optical behavior and phase purity have been elucidated using SEM, TEM, XPS, UV-DRD, PL and XRD spectra, respectively. Among all, Ni 3 S 2 /CNT50 composite counter electrode delivers the highest Power Conversion Efficiency (PCE) of 9.28 ± 0.03% with a short circuit current (J SC ) of 18.46 ± 0.01 mAcm −2 and open-circuit voltage (V OC ) of 0.73 ± 0.01 V. The improvement observed is due to the lower peak-to-peak separation (E pp ), higher exchange current density (J 0 ) and lower charge transfer resistance (R CT ). External quantum efficiency and electrochemical impedance analysis for the boost in efficiency and improved electrocatalytic activity with low charge-transfer resistance at (CE)/electrolyte interface are well in support for the synergistic effect of Ni 3 S 2 and MWCNTs.

Double-Side Selective Spectral Response Organic Photodetectors for Demultiplexing Optical Signals.

Selective spectral response photodetectors (PDs) capable of accurately capturing the color of images have broad applications in industry and academia. Here, we demonstrate filter-free, wavelength-selective detection organic photodetectors (OPDs) with two distinct response ranges and having the planar bilayer heterojunction device structure by employing either a (semi-)transparent anode or a cathode as the incident light window. The resultant OPDs exhibit a responsivity of 51 mA W-1 in the range 300-650 nm and 11 mA W-1 in the range 650-850 nm under top illumination condition. Similarly, the devices show a responsivity of 2 mA W-1 for the short-wavelength region and 131 mA W-1 for the long-wavelength region when under bottom illumination condition, indicating a high responsivity ratio that meets the requirements for selective detection. Hence, our individual device not only works in either visible or NIR range but also provides narrowband detection with spectral widths down to 100 nm in the NIR range. The working mechanism of spectral selectivity is identified through quantitative analysis of the external quantum efficiency (EQE) spectra using optical modeling when compared to the OPDs with bulk heterojunction structure, thus clarifying the general validity of the device design concept. Finally, our OPDs can demultiplex intermixed optical signals from the light-communication system successfully. Our results should inspire new studies on the device design concept and new applications of OPDs.

Photoemission from GaAs-based photocathodes with multilayer complex structures

To enhance the near-infrared response of photocathodes in the application of image detection, two kinds of multilayer complex structures of GaAs-based photocathodes are developed by changing the structure of the buffer layer underneath the emission layer, wherein one is the graded bandgap structure, and the other is the distributed Bragg reflector (DBR) structure. The theoretical quantum efficiency suitable for the reflection-mode (r-mode) GaAs-based photocathode with these two kinds of buffer structures are deduced based on one-dimensional continuity equations, among which the reflectivity changing with the wavelength of incident light is considered in particular. By comparison of spectral characteristics of photocathodes with the two different structures, and analysis of cathode structure parameters, it is found that the photoelectric performance of the photocathodes with the two structures are quite different, and the structure parameters especially the thickness of GaAs emission layer have a great impact on the spectral characteristic. The quantum efficiency of photocathode with graded bandgap structure is improved due to the introduction of the built-in electric field and the decrement of interface recombination, while for cathode with DBR structure, the quantum efficiency is improved by the multiple reflection of light between two parallel mirrors in the stack of alternating quarter-wave layers of high and low refractive. The theoretical quantum efficiency calculation and analysis would provide theoretical guidance for the better design of GaAs-based photocathodes.

Analysis of Size-Dependent Quantum Efficiency in AlGaInP Micro–Light-Emitting Diodes With Consideration for Current Leakage

This study fabricated and analyzed AlGaInP-based red micro–light-emitting diodes (LEDs) ranging from 2 to 15 μm in size. To collect photons from a single micro-LED at this scale, a solar cell chip near the micro-LEDs was used. Quantum efficiency decreased at a faster rate than that predicted by the standard ABC model under high currents, and a leakage current component was added to fully describe this phenomenon. The modified model can be used to extract valuable information regarding the micro-LEDs, such as the Shockley–Read–Hall coefficient. A size dependency analysis revealed that the bulk Shockley–Read–Hall coefficient and surface recombination velocity of the micro-LEDs were 6.81 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> 1/sec and 5.99 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> cm/sec, respectively. Further analysis of the size-dependent recombination effect can help us solve the side wall problem and maximize the light output of AlGaInP-based micro-LEDs for ultrahigh-resolution displays.

Quantum Efficiency Simulation and Analysis of Irradiated Complementary Metal-Oxide Semiconductor Image Sensors

A quantum efficiency model of complementary metal-oxide semiconductor image sensors based on Shockley–Read–Hall and Auger recombination is developed using the technology computer-aided design tool, and the quantum efficiency degradation after irradiation is analyzed. By simulating the surface recombination velocity and depletion region width of the photodiode, the decrease in the quantum efficiency of complementary metal-oxide semiconductor image sensors under short and long incident light wavelengths is found to be caused by the increase in the surface recombination velocity and capture of optical carriers by radiation-induced defects in the epitaxial layer, respectively. In addition, a method to reduce the quantum efficiency degradation behavior of an irradiated pixel is discussed.

Characterizing and Improving the Thermal Stability of Organic Photovoltaics Based on Halogen-Rich Non-Fullerene Acceptors.

The thermal stability of inverted, halogen-rich non-fullerene acceptor (NFA)-based organic photovoltaics with MoOx as the hole transporting layer is studied at temperatures up to 80 °C. Over time, the power conversion efficiency shows a "check-mark" shaped thermal aging pattern, featuring an early decrease, followed by a long-term recovery. A high Cl concentration at the bulk heterojunction (BHJ)/MoOx interface in the thermally aged device is found using energy dispersive X-ray spectroscopy. X-ray photoelectron spectroscopy shows that the MoOx is chlorinated after thermal aging. With bulk quantum efficiency analysis, we propose an explanation to the check-mark shaped pattern. Inserting a thin C70 layer between the BHJ and MoOx suppresses the thermal degradation mechanisms, resulting in three orders of magnitude increase in device lifetime at 80 °C.

Analysis of internal optical loss of 1.3 μm vertical-cavity surface-emitting laser based on n-=SUP=-++-=/SUP=--InGaAs/p-=SUP=-++-=/SUP=--InGaAs/p-=SUP=-++-=/SUP=--InAlGaAs tunnel junction

The analysis of internal optical loss and internal quantum efficiency in 1.3 μm-range InAlGaAsP/AlGaAs a composite n+-InGaAs/p+-InGaAs/p+-InAlGaAs tunnel junction obtained in the frame of molecular-beam epitaxy and wafer fusion technology. The level of internal optical losses in the lasers under study was varied by depositing a dielectric layer on the surface of the output mirror. It is shown that it is possible in principle to achieve low internal optical loss of less than 0.08% and 0.14% per one pass (round-trip) at temperatures of 20oC and 90oC, respectively. Keywords: vertical-cavity surface-emitting laser, wafer fusion, tunnel junction, superlattice, internal optical loss.

MoS2 nanoflakes anchored MWCNTs: Counter electrode in dye-sensitized solar cell

Simple chemical bath deposition method has been demonstrated to anchor MoS2 nanoflakes over ‘dip and dry’ coated thin-film of MWCNTs at room temperature (~30 ℃) to use as a counter electrode (CE) in ZnO/Eosin-Y photoanode based dye-sensitized solar cells (DSSCs) as the first report. Obtained materials are well confirmed through XRD, FESEM, TEM, and XPS analysis. Two-step chemical route explores the easy way of CE fabrication. DSSCs fabricated with MoS2/MWCNTs CE have gained more than three times (0.56%) power conversion efficiency compared to the bare MWCNTs CE (0.15%). External quantum efficiency and electrochemical impedance analysis for the boost in efficiency and improved electrocatalytic activity with low charge-transfer resistance at (CE)/ electrolyte interface are well in support for the synergistic effect of MoS2 and MWCNTs.

Characterization of Potential-Induced Degradation and Recovery in CIGS Solar Cells

The potential-induced degradation (PID) mechanism in Cu(In,Ga)(Se,S)2 (CIGS) thin-film solar cells, which are alternative energy sources with a high efficiency (&gt;23%) and upscaling possibilities, remains unclear. Therefore, the cause of PID in CIGS solar cells was investigated in this study at the cell level. First, an appropriate PID experiment structure at the cell level was determined. Subsequently, PID and recovery tests were conducted to confirm the PID phenomenon. Light current–voltage (I–V), dark I–V, and external quantum efficiency (EQE) analyses were conducted to determine changes in the cell characteristics. In addition, capacitance–voltage (C–V) measurements were carried out to determine the doping concentration and width of the space charge region (SCR). Based on the results, the causes of PID and recovery of CIGS solar cells were explored, and it was found that PID occurs due to changes in the bulk doping concentration and built-in potential at the junction. Furthermore, by distinguishing the effects of temperature and voltage, it was found that PID phenomena occurred when potential difference was involved.

Анализ внутренних оптических потерь вертикально-излучающего лазера спектрального диапазона 1.3 &amp;mu;m с туннельным переходом на основе слоев n-=SUP=-+-=/SUP=--InGaAs/p-=SUP=-+-=/SUP=--InGaAs/p-=SUP=-+-=/SUP=--InAlGaAs

The analysis of internal optical loss and internal quantum efficiency in 1.3 μm-range InAlGaAsP/AlGaAs a composite n++-InGaAs/р++-InGaAs/р++-InAlGaAs tunnel junction obtained in the frame of molecular-beam epitaxy and wafer fusion technology. The level of internal optical losses in the lasers under study was varied by depositing a dielectric layer on the surface of the output mirror. It is shown that it is possible in principle to achieve low internal optical loss of less than 0.08% and 0.14% per one pass (round-trip) at temperatures of 20°С and 90°С, respectively.

Internal quantum efficiency and time signals from intensity-modulated photocurrent spectra of perovskite solar cells

Intensity Modulated Photocurrent Spectroscopy (IMPS) is a small-perturbation optoelectronic technique that measures the quantum efficiency of a photoelectrochemical device as a function of optical excitation frequency. Metal Halide Perovskites (MHPs) are mixed electronic–ionic semiconductors with an extraordinary complex optoelectronic behavior and a record efficiency surpassing 25%. In this paper, we propose a simplified procedure to analyze IMPS data in MHPs based on the analysis of the internal quantum efficiency and the time signals featuring in the frequency spectra. In this procedure, we look at the change of each signal when optical excitation wavelength, photon flux, and temperature are varied for an archetypical methyl ammonium lead iodide solar cell. We use drift-diffusion modeling and comparison with relatively simpler dye-sensitized solar cells (DSC) with viscous and non-viscous electrolytes to help us to understand the origin of the three signals appearing in MHP cells and the measurement of the internal quantum efficiency.

Morphological control of Cu2ZnSn(S,Se)4 absorber films via inverted annealing for high-performance solar cells

In recent years, the method of forming Cu2ZnSn(S,Se)4 (CZTSSe) by heating precursors has been widely used, but the chalcogen vapor conditions and the placement of the sample have not been disclosed completely. Here, we demonstrate a novel inverted annealing process that enables the reaction between the chalcogen vapor and precursors to remain constant. As a result, we obtained CZTSSe absorber films with an improved morphology and a uniformly distributed elemental composition. The inverted annealed samples showed less variation in the S and Se content as well as in the statistical analysis of the device performance compared with those prepared via the original annealing process. These variations in the S and Se content were confirmed several times through X-ray diffraction, energy-dispersive X-ray, and external quantum efficiency analysis. A pn-junction analysis using a Mott-Schottky plot was also conducted. We anticipate that the inverted annealing process will become widely used as it is easily applicable and effective in improving the morphology of CZTSSe absorber films.

Fast Field-Insensitive Charge Extraction Enables High Fill Factors in Polymer Solar Cells.

Fill factor (FF) is a determining parameter for the power conversion efficiency (PCE) of organic solar cells (OSC). So far, nonfullerene (NF) OSCs with state-of-the-art PCEs exhibit FFs <0.8, lower than the values of Si or perovskite solar cells. The FFs directly display the dependence of photocurrent on bias, meaning that the competition between charge extraction and recombination is modulated by internal electric potential (Vin). Here, we report a study to understand key parameters/properties affecting the device FF based on seven groups of NF-OSCs consisting of widely used PBDBT-2F or PTB7-Th donors and representative NF-acceptors with FFs ranging from 0.60 to 0.78 and PCEs from 10.27 to 16.09%. We used field-dependent transient photocurrent measurements to reveal that fast and field-insensitive charge extraction at low Vin is an essential prerequisite for obtaining high FFs (0.75-0.8), which is enabled by balanced charge transport in steady and reduced bimolecular charge recombination in high purity phases. With bias-dependent quantum efficiency analysis, we further show that the recombination loss at low Vin in the devices with low FFs tends to be more significant involving excitons generated in the donor phase of blends. Our results provide relevance for how to improve the FF toward the boost of photovoltaic performance in NF-OSCs.

Ultra-thin MoS2 nanosheet for electron transport layer of perovskite solar cells

The structure and the physical dimension of the electron transport layer (ETL) in perovskite solar cell (PSC) determine the carrier transport characteristics to the electrode and then the overall performance of the device. ETL with ultimately thin and single-crystalline should facilitate enhanced photogenerated carrier transport to the electrode, inducing a highly dynamic charge transfer at the interface of ETL and perovskite absorber layer. Here, we demonstrated that a planar few atoms (5 monolayer or 5L) thick MoS2 nanosheets synthesized directly onto the ITO substrate allows a facile interfacial charge transfer and transport as judged from the open circuit voltage (Voc) value, steady-state photoluminescence and external quantum efficiency (EQE) analysis results. We found that the nanosheets crystallinity properties determines the photoelectrical process in the PSC device. The champion device in this study can produce a power conversion efficiency (PCE) as high as 3.36% with a short-circuit current density (Jsc), open circuit voltage (Voc) and fill-factor (FF) of as high as 16.24 mA cm−2, 0.56 V and 0.370, respectively. The champion device also exhibited a reasonable high stability properties that shows it can retain more than 90% of its initial PCE when operated under irradiation of 1 sun at maximum power-point. Due to the single crystallinity and the large area properties, the MoS2 nanosheets prepared using the present method may find extended application as high-performance ETL of perovskite solar cells.