Application of Bifacial Semitransparent CuInSe2 Absorber to the Bottom Cell in Bifacial Semitransparent Perovskite/CuInSe2 Tandem Solar Cell for Albedo Environment.

Although various types of bifacial solar cells exist, few studies have been conducted on bifacial semitransparent CuInSe2 solar cells (BS-CISe SCs) despite the attractive potential in power generation from both sides in an albedo environment. The optimized BS-CISe SCs with 300 and 800 nm-thick absorber via a streamlined single-stage co-evaporation process exhibit a power conversion efficiency (PCE) of 6.32% and 10.6%, respectively. When double-sided total 2.0 sun illumination is assumed in an albedo environment, the bifacial power generation densities (BPGD) of them increases to 9.41% and 13.9%. Four-terminal bifacial semitransparent tandem solar cells (4T-BST SCs) are fabricated to increase the BPGD by mechanically stacking a BS-perovskite (PVK) top cell on top of a BS-CISe bottom cell with the 300 and 800 nm-thick absorber layers. When summed up, the best top and bottom cell PCEs of the 4T-BST SC with 300 and 800 nm-thick BS-CISe SC are 18.8% and 21.1%, respectively. However, the practical BPGD values of the 4T-BST SC under total 2 sun illumination are interestingly 23.4% and 24.4%, respectively. This is because the BS-CISe bottom cell's thickness affects how much rear-side illumination is transmitted to the BS-PVK top cell, increasing its current density and BPGD.

Toward Ultrahigh Thermoelectric Performance of Cu2 SnS3 -Based Materials by Analog Alloying.

Cu2 SnS3 is a promising thermoelectric candidate for power generation at medium temperature due to its low-cost and environmental-benign features. However, the high electrical resistivity due to low hole concentration severely restricts its final thermoelectric performance. Here, analog alloying with CuInSe2 is first adopted to optimize the electrical resistivity by promoting the formation of Sn vacancies and the precipitation of In, and optimize lattice thermal conductivity through the formation of stacking faults and nanotwins. Such analog alloying enables a greatly enhanced power factor of 8.03 µW cm-1 K-2 and a largely reduced lattice thermal conductivity of 0.38 W m-1  K-1 for Cu2 SnS3 - 9 mol.% CuInSe2 . Eventually, a peak ZT as high as 1.14 at 773 K is achieved for Cu2 SnS3 - 9 mol.% CuInSe2 , which is one of the highest ZT among the researches on Cu2 SnS3 -based thermoelectric materials. The work implies analog alloying with CuInSe2 is a very effective route to unleash superior thermoelectric performance of Cu2 SnS3 .

High-resolution XEOL spectroscopy setup at the X-ray absorption spectroscopy beamline P65 of PETRA III.

A newly designed setup to perform steady-state X-ray excited optical luminescence (XEOL) spectroscopy and simultaneous XEOL and X-ray absorption spectroscopy characterization at beamline P65 of PETRA III is described. The XEOL setup is equipped with a He-flow cryostat and state-of-the-art optical detection system, which covers a wide wavelength range of 300-1700 nm with a high spectral resolution of 0.4 nm. To demonstrate the setup functioning, low-temperature XEOL studies on polycrystalline CuInSe2 thin film, single-crystalline GaN thin film and single-crystalline ZnO bulk semiconductor samples are performed.

Near-Infrared Nanophosphors Based on CuInSe2 Quantum Dots with Near-Unity Photoluminescence Quantum Yield for Micro-LEDs Applications.

Highly efficient near-infrared (NIR) luminescent nanomaterials are urgently required for portable mini or micro phosphors-converted light-emitting diodes (pc-LEDs). However, most existing NIR-emitting phosphors are generally restricted by their low photoluminescence (PL) quantum yield (QY) or large particle size. Herein, a kind of highly efficient NIR nanophosphors is developed based on copper indium selenide quantum dots (CISe QDs). The PL peak of these QDs can be exquisitely manipulated from 750 to 1150 nm by altering the stoichiometry of Cu/In and doping with Zn2+ . Their absolute PLQY can be significantly improved from 28.6% to 92.8% via coating a ZnSe shell. By combining the phosphors with a commercial blue chip, an NIR pc-LED is fabricated with remarkable photostability and a record-high radiant flux of 88.7 mW@350 mA among the Pb/Cd-free QDs-based NIR pc-LEDs. Particularly, such QDs-based nanophosphors acted as excellent luminescence converter for NIR micro-LEDs with microarray diameters below 5 µm, which significantly exceeds the resolutions of current commercial inkjet display pixels. The findings may open new avenues for the exploration of highly efficient NIR micro-LEDs in a variety of applications.

Recent developments in colloidal synthesis of CuInSe2 nanoparticles.

Ternary semiconductor nanocrystals, such as CuInSe2 , are of high interest for photovoltaic application due to their relatively low toxicity and unique properties. During the last decades great success has been achieved in the colloidal synthesis of binary nanoparticles, but for ternary compounds this research is still in an early stage of development. These materials are a challenge for synthetic chemistry, because the interaction between the three components (copper, indium, and selenium) plays a major role for the production of high quality material. The purpose of this Minireview is to provide a summary of the achievements in colloidal synthesis of CuInSe2 nanoparticles--in particular, details of reaction mechanism and its characterization possibilities, which might be useful also for the colloidal synthesis of other multicomponent systems.

Effects of Mono- and Bifunctional Surface Ligands of Cu-In-Se Quantum Dots on Photoelectrochemical Hydrogen Production.

Semiconductor nanocrystal quantum dots (QDs) are promising materials for solar energy conversion because of their bandgap tunability, high absorption coefficient, and improved hot-carrier generation. CuInSe2 (CISe)-based QDs have attracted attention because of their low toxicity and wide light-absorption range, spanning visible to near-infrared light. In this work, we study the effects of the surface ligands of colloidal CISe QDs on the photoelectrochemical characteristics of QD-photoanodes. Colloidal CISe QDs with mono- and bifunctional surface ligands are prepared and used in the fabrication of type-II heterojunction photoanodes by adsorbing QDs on mesoporous TiO2. QDs with monofunctional ligands are directly attached on TiO2 through partial ligand detachment, which is beneficial for electron transfer between QDs and TiO2. In contrast, bifunctional ligands bridge QDs and TiO2, increasing the amount of QD adsorption. Finally, photoanodes fabricated with oleylamine-passivated QDs show a current density of ~8.2 mA/cm2, while those fabricated with mercaptopropionic-acid-passivated QDs demonstrate a current density of ~6.7 mA/cm2 (at 0.6 VRHE under one sun illumination). Our study provides important information for the preparation of QD photoelectrodes for efficient photoelectrochemical hydrogen generation.

Photonic Lift-off Process to Fabricate Ultrathin Flexible Solar Cells.

A microsecond time-scale photonic lift-off (PLO) process was used to fabricate mechanically flexible photovoltaic devices (PVs) with a total thickness of less than 20 µm. PLO is a rapid, scalable photothermal technique for processing extremely thin, mechanically flexible electronic and optoelectronic devices. PLO is also compatible with large-area devices, roll-to-roll processing, and substrates with low temperature compatibility. As a proof of concept, PVs were fabricated using CuInSe2 nanocrystal ink deposited at room temperature under ambient conditions on thin, plastic substrates heated to 100 °C. It was necessary to prevent cracking of the brittle top contact layer of indium tin oxide (ITO) during lift-off, either by using a layer of silver nanowires (AgNW) as the top contact or by infusing the ITO layer with AgNW. This approach could generally be used to improve the mechanical versatility of current collectors in a variety of ultrathin electronic and optoelectronic devices requiring a transparent conductive contact layer.

Transient Lattice Response upon Photoexcitation in CuInSe2 Nanocrystals with Organic or Inorganic Surface Passivation.

CuInSe2 nanocrystals offer promise for optoelectronics including thin-film photovoltaics and printed electronics. Additive manufacturing methods such as photonic curing controllably sinter particles into quasi-continuous films and offer improved device performance. To gain understanding of nanocrystal response under such processing conditions, we investigate impacts of photoexcitation on colloidal nanocrystal lattices via time-resolved X-ray diffraction. We probe three sizes of particles and two capping ligands (oleylamine and inorganic S2-) to evaluate resultant crystal lattice temperature, phase stability, and thermal dissipation. Elevated fluences produce heating and loss of crystallinity, the onset of which exhibits particle size dependence. We find size-dependent recrystallization and cooling lifetimes ranging from 90 to 200 ps with additional slower cooling on the nanosecond time scale. Sulfide-capped nanocrystals show faster recrystallization and cooling compared to oleylamine-capped nanocrystals. Using these lifetimes, we find interfacial thermal conductivities from 3 to 28 MW/(m2 K), demonstrating that ligand identity strongly influences thermal dissipation.

Broad-Band Photodetectors Based on Copper Indium Diselenide Quantum Dots in a Methylammonium Lead Iodide Perovskite Matrix.

Low-temperature solution-processed methylammonium lead iodide (MAPbI3) crystalline films have shown outstanding performance in optoelectronic devices. However, their high dark current and high noise equivalent power prevent their application in broad-band photodetectors. Here, we applied a facile solution-based antisolvent strategy to fabricate a hybrid structure of CuInSe2 quantum dots (CISe QDs) embedded into a MAPbI3 matrix, which not only enhances the photodetector responsivity, showing a large on/off ratio of 104 at 2 V bias compared with the bare perovskite films, but also significantly (for over 7 days) improves the device stability, with hydrophobic ligands on the CuInSe2 QDs acting as a barrier against the uptake of environmental moisture. MAPbI3/CISe QD-based lateral photodetectors exhibit high responsivities of >0.5 A/W and 10.4 mA/W in the visible and near-infrared regions, respectively, partly because of the formation of a type II interface between the respective semiconductors but most significantly because of the efficient trap-state passivation of the perovskite grain surfaces, and the reduction in the twinning-induced trap density, which stems from both CISe QDs and their organic ligands. A large specific detectivity of 2.2 × 1012 Jones at 525 nm illumination (1 µW/cm2), a fast fall time of 236 µs, and an extremely low noise equivalent power of 45 fW/Hz1/2 have been achieved.

Efficient detection doxorubicin hydrochloride using CuInSe2@ZnS quantum dots and Ag nanoparticles.

Doxorubicin hydrochloride (DOX) is an effective anthracycline anticancer drug. However, the exceeded taken up could induce several side-effects such as cardiotoxicity, alopecia. Therefore, the level of DOX needs to be closely monitored to avoid the occurrence of its side-effects. Herein, we report a novel core CuInSe2 - shell ZnS quantum dots (CuInSe2@ZnS, QDs) and Ag nanoparticles (NPs) fluorescence sensor based on the surface plasmon resonance effect (SPR) of Ag NPs. The CuInSe2@ZnS QDs were prepared by water phase reflux method with the 3-mercaptopropionic acid (MPA) as stabilizer and ligand. The fluorescence intensity of CuInSe2@ZnS QDs/Ag NPs significantly reduced by DOX, which is mainly based on the electrostatic interaction between the DOX and fluorescence sensors. The inhibition of photoluminescence (ln F0/F) was linearly relationship to the concentration of DOX in the range of 2-100 µM with the detection limit as low as 0.05 µM. The as-prepared sensor has a high selectivity and sensitivity to DOX. Furthermore, the new sensor has been successfully applied to the determination of DOX in human serum samples with satisfactory results. Our work provides a clue for developing a novel CuInSe2@ZnS QDs/Ag NPs based fluorescence sensor for DOX detection.

High-Performance Broadband Photodetector Based on Monolayer MoS2 Hybridized with Environment-Friendly CuInSe2 Quantum Dots.

Monolayer MoS2, a direct bandgap transition metal dichalcogenide (TMD), has attracted worldwide attention in electronics and optoelectronics. However, the performance of photodetectors based on monolayer MoS2 is restricted to a weak optical absorption, narrow absorption range, and persistent photoconductance. Herein, benefiting from an easy solution process, high light absorption coefficient, and wide absorption range, environment-friendly CuInSe2 quantum dots (QDs) are hybridized with monolayer MoS2 for high-performance broadband photodetectors. Owing to the favorable type-II energy band alignment of MoS2/CuInSe2-QDs, the hybrid photodetector exhibits a broadband photoresponse from the ultraviolet to near-infrared region, with an ultrahigh photoresponsivity of 74.8 A/W at 1064 nm, and compared with those of the pristine MoS2 device, the photoresponsivity and specific detectivity in the ultraviolet-visible region were enhanced by about 30 and 20 times, respectively. Furthermore, the formed depletion region at the MoS2/CuInSe2-QDs interface can significantly increase the photoresponse speed, and the accumulated holes in the QD side induce a strong photogating effect to improve the photoresponsive characteristics of the hybrid photodetector. Our work opens up opportunities for fabricating high-performance monolayer TMD-based broadband photodetectors.

SDS-Stabilized CuInSe2/ZnS Multinanocomposites Prepared by Mechanochemical Synthesis for Advanced Biomedical Application.

The CuInSe2/ZnS multiparticulate nanocomposites were first synthesized employing two-step mechanochemical synthesis. In the first step, tetragonal CuInSe2 crystals prepared from copper, indium and selenium precursors were co-milled with zinc acetate dihydrate and sodium sulfide nonahydrate as precursors for ZnS in different molar ratios by mechanochemical route in a planetary mill. In the second step, the prepared CuInSe2/ZnS nanocrystals were further milled in a circulation mill in sodium dodecyl sulphate (SDS) solution (0.5 wt.%) to stabilize the synthesized nanoparticles. The sodium dodecyl sulphate capped CuInSe2/ZnS 5:0-SDS nanosuspension was shown to be stable for 20 weeks, whereas the CuInSe2/ZnS 4:1-SDS one was stable for about 11 weeks. After sodium dodecyl sulphate capping, unimodal particle size distribution was obtained with particle size medians approaching, respectively, 123 nm and 188 nm for CuInSe2/ZnS 5:0-SDS and CuInSe2/ZnS 4:1-SDS nanocomposites. Successful stabilization of the prepared nanosuspensions due to sodium dodecyl sulphate covering the surface of the nanocomposite particles was confirmed by zeta potential measurements. The prepared CuInSe2/ZnS 5:0-SDS and CuInSe2/ZnS 4:1-SDS nanosuspensions possessed anti-myeloma sensitizing potential assessed by significantly reduced viability of multiple myeloma cell lines, with efficient fluorescence inside viable cells and higher cytotoxic efficacy in CuInSe2/ZnS 4:1-SDS nanosuspension.

Diffusion of Alkali Metals in Polycrystalline CuInSe2 and Their Role in the Passivation of Grain Boundaries.

The behavior of alkali atom point defects in polycrystalline CuInSe2 is studied. In this work, three grain boundary models, one coherent twin boundary and two twin boundaries with dislocation cores, are considered. Total energy calculations show that all alkali metals tend to segregate at the grain boundaries. In addition, the segregation of alkali atoms is more pronounced at the grain boundaries with the dislocation cores. The diffusion of alkali metals along and near grain boundaries is studied as well. The results show that the diffusion of alkali atoms in the grain boundary models is faster than within the bulk. In addition, the ion exchange between Na and Rb atoms at the grain boundaries leads to the Rb enrichment at the grain boundaries and the increase of the Na concentration in the bulk. While the effects of Na and Rb point defects on the electronic structure of the grain boundary with the anion-core dislocation are similar, Rb atoms passivate the grain boundary with the cation-core dislocation more effectively than Na. This can explain the further improvement of the solar cell performance after the RbF-postdeposition treatment.

CuInSe2 quantum dots grown by molecular beam epitaxy on amorphous SiO2 surfaces.

The currently most efficient polycrystalline solar cells are based on the Cu(In,Ga)Se2 compound as a light absorption layer. However, in view of new concepts of nanostructured solar cells, CuInSe2 nanostructures are of high interest. In this work, we report CuInSe2 nanodots grown through a vacuum-compatible co-evaporation growth process on an amorphous surface. The density, mean size, and peak optical emission energy of the nanodots can be controlled by changing the growth temperature. Scanning transmission electron microscopy measurements confirmed the crystallinity of the nanodots as well as chemical composition and structure compatible with tetragonal CuInSe2. Photoluminescence measurements of CdS-passivated nanodots showed that the nanodots are optoelectronically active with a broad emission extending to energies above the CuInSe2 bulk bandgap and in agreement with the distribution of sizes. A blue-shift of the luminescence is observed as the average size of the nanodots gets smaller, evidencing quantum confinement in all samples. By using simple quantum confinement calculations, we correlate the photoluminescence peak emission energy with the average size of the nanodots.

CuInSe2 Quantum Dots Hybrid Hole Transfer Layer for Halide Perovskite Photodetectors.

A novel hybrid hole transport layer (HTL) of CuInSe2 quantum dots (QDs)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was developed to enhance the performance of halide metal perovskite (MAPbI3)-based photodetectors. The introduction of CuInSe2 QDs not only improved the wettability of the PEDOT:PSS HTL for the growth of perovskite crystals but also facilitated the transportation of holes from the perovskite to the HTL. As a result, both responsivity and detectivity of the device were increased dramatically by CuInSe2 QDs hybrid HTL, showing excellent photoresponsivity of 240 mA/W, larger ratio of photocurrent density to dark current density of 4.1 × 106, fast on-off switching properties of <0.02 s, and remarkable detectivity values of 1.02 × 1013 Jones at 580 nm and above 5.01 × 1012 Jones over the visible light region without an external bias voltage. In addition, the photodetectors also showed excellent thermal stability in the range of 10-110 °C. Therefore, a unique design idea of a hole transport material would be an anticipated direction for efficient halide metal perovskite-based devices.

Self-Assembly of the Lateral In2Se3/CuInSe2 Heterojunction for Enhanced Photodetection.

Layered materials have been found to be promising candidates for next-generation microelectronic and optoelectronic devices due to their unique electrical and optical properties. The p-n junction is an elementary building block for microelectronics and optoelectronics devices. Herein, using the pulsed-laser deposition (PLD) method, we achieve pure In2Se3-based photodetectors and In2Se3/CuInSe2-based photodetectors with a lateral p-n heterojunction. In comparison to that of the pure In2Se3-based photodetector, the photodetectors based on the In2Se3/CuInSe2 heterojunction exhibit a tremendous promotion of photodetection performance and obvious rectifying behavior. The photoresponsivity and external quantum efficiency of the fabricated heterojunction-based device under 532 nm light irradiation are 20.1 A/W and 4698%, respectively. These values are about 7.5 times higher than those of our fabricated pure In2Se3-based devices. We attribute this promotion of photodetection to the suitable band structures of In2Se3 and CuInSe2, which greatly promote the separation of photoexcited electron-hole pairs. This work suggests an effective way to form lateral p-n junctions, opening up a new scenario for designing and constructing high-performance optoelectronic devices.

Suppressed Formation of Conductive Phases in One-Pot Electrodeposited CuInSe2 by Tuning Se Concentration in Aqueous Electrolyte.

The single-bath electrochemical deposition of CuInSe2 often leads to short-circuit behavior of the resulting solar cells due to the high shunt conductance. In this study, in an attempt to resolve this problem, the influence of the Se precursor concentration (CSe) on electrodeposited CuInSe2 films and solar cell devices is examined in the CSe range of 4.8 to 12.0 mM in selenite-based aqueous solutions containing Cu and In chlorides along with sulfamic acid (H3NSO3) and potassium hydrogen phthalate (C8H5KO4) additives. As CSe increases, the CuInSe2 layers become porous, and the grain growth of the CuInSe2 phase is restricted, while the parasitic shunting problem was markedly alleviated, as unambiguously demonstrated by measurements of the local current distribution. Due to these ambivalent influences, an optimal value of CSe that achieves the best quality of the films for high-efficiency solar cells is identified. Thus, the device prepared with 5.2 mM Se exhibits a power-conversion efficiency exceeding 10% with greatly improved device parameters, such as the shunt conductance and the reverse saturation current. The rationale of the present approach along with the physicochemical origin of its conspicuous impact on the resulting devices is discussed in conjunction with the electro-crystallization mechanism of the CuInSe2 compound.

Tuning carrier mobilities and polarity of charge transport in films of CuInSe(x)S(2-x) quantum dots.

CuInSe(x)S(2-x) quantum dot field-effect transistors show p-type, n-type, and ambipolar behaviors with carrier mobilities up to 0.03 cm(2) V(-1) s(-1). Although some design rules from studies of cadmium and lead containing quantum dots can be applied, remarkable differences are observed including a strong gating effect in as-synthesized nanocyrstals with long ligands.

Fabrication of CIS Absorber Layers with Different Thicknesses Using A Non-Vacuum Spray Coating Method.

In this study, a new thin-film deposition process, spray coating method (SPM), was investigated to deposit the high-densified CuInSe2 absorber layers. The spray coating method developed in this study was a non-vacuum process, based on dispersed nano-scale CuInSe2 precursor and could offer a simple, inexpensive, and alternative formation technology for CuInSe2 absorber layers. After spraying on Mo/glass substrates, the CuInSe2 thin films were annealed at 550 °C by changing the annealing time from 5 min to 30 min in a selenization furnace, using N2 as atmosphere. When the CuInSe2 thin films were annealed, without extra Se or H2Se gas used as the compensation source during the annealing process. The aim of this project was to investigate the influence of annealing time on the densification and crystallization of the CuInSe2 absorber layers to optimize the quality for cost effective solar cell production. The thickness of the CuInSe2 absorber layers could be controlled as the volume of used dispersed CuInSe2-isopropyl alcohol solution was controlled. In this work, X-ray diffraction patterns, field emission scanning electron microscopy, and Hall parameter measurements were performed in order to verify the quality of the CuInSe2 absorber layers obtained by the Spray Coating Method.

Photocharging Artifacts in Measurements of Electron Transfer in Quantum-Dot-Sensitized Mesoporous Titania Films.

Transient absorption and time-resolved photoluminescence measurements of high-performance mesoporous TiO2 photoanodes sensitized with CuInSexS2-x quantum dots reveal the importance of hole scavenging in the characterization of photoinduced electron transfer. The apparent characteristic time of this process strongly depends on the local environment of the quantum dot/TiO2 junction due to accumulation of long-lived positive charges in the quantum dots. The presence of long-lived photoexcited holes introduces artifacts due to fast positive-trion Auger decay (60 ps time constant), which can dominate electron dynamics and thus mask true electron transfer. We show that the presence of a redox electrolyte is critical to the accurate characterization of charge transfer, since it enables fast extraction of holes and helps maintain charge neutrality of the quantum dots. Although electron transfer is observed to be relatively slow (19 ns time constant), a high electron extraction efficiency (>95%) can be achieved because in well-passivated CuInSexS2-x quantum dots neutral excitons have significantly longer lifetimes of hundreds of nanoseconds.