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For cuboid and ellipsoid crystallites of LiFePO4 powders, by X-ray diffraction (XRD) and microscopic (TEM) studies, it is possible to determine the anisotropic parameters of the crystallite size distribution functions. These parameters were used to describe the cathode rate capability within the model of averaging the diffusion coefficient D over the length of the crystallite columns along the [010] direction. A LiFePO4 powder was chosen for testing the developed model, consisting of big cuboid and small ellipsoid crystallites (close to them). When analyzing the parts of big and small rate capabilities, the fitting values D = 2.1 and 0.3 nm2/s were obtained for cuboids and ellipsoids, respectively. When analyzing the results of cyclic voltammetry using the Randles-Sevcik equation and the total area of projections of electrode crystallites on their (010) plane, slightly different values were obtained, D = 0.9 ± 0.15 and 0.5 ± 0.15 nm2/s, respectively. We believe that these inconsistencies can be considered quite acceptable, since both methods of determining D have obvious sources of error. However, the developed method has a clearly lower systematic error due to the ability to actually take into account the shape and statistics of crystallites, and it is also useful for improving the accuracy of the Randles-Sevcik equation. It has also been demonstrated that the shape engineering of crystallites, among other tasks, can increase the cathode capacity by 15% by increasing their size correlation coefficients.

The efficiency of solution-processed colloidal quantum dot (CQD) thin-film solar cells has been significantly improved recently. However, there is still potential for efficiency improvements, which can be realized through a deeper understanding of surface chemical treatment for CQDs. In this study, we developed CQD thin-film solar cells with an improved power conversion efficiency (PCE) of 11.97%. We accomplished this by simply controlling the species and their molar concentrations used in the surface chemical treatment in the solutionphase ligand exchange process. Iodine treatment that generates conductive CQDs induces surface defects via cationic decomposition of the CQD surface; healing the CQD surface requires an excess of lead cations in the solution-phase ligand exchange process. Accordingly, we found that manufacturing CQD thin-film solar cells that have high efficiencies requires well-controlled surface treatment to effectively exchange surface ligands and simultaneously minimize surface defects on the CQD surface.

The crucial issue of wettability in high-energy-density lithium-ion batteries (LIBs) has not been comprehensively addressed to date. To overcome the challenge, state-of-the-art LIBs employing a ceramic-coated separator improves the safety- and wettability-related aspects of LIBs. Here, we present a mechanistic study of the effects of a ceramic-coated layer (CCL) on electrode wettability and report the optimal position of the CCL in LIBs. The electrolyte wetting was investigated using the multiphase lattice Boltzmann method and electrochemical impedance spectroscopy for capturing the electrolyte-transport dynamics in porous electrodes and impedance spectra in pouch-type LIBs, respectively. Results indicate that the CCL caused the velocity vector to transport the electrolyte further, resulting in an increase in the wetting rate. Moreover, the location of the CCL considerably affected the wettability of the LIBs. This study provides mechanical insight into the design and fabrication of high-performance LIBs by incorporating CCLs.

We investigated the heat dissipation in heterostructure field-effect transistors (HFETs) using microRaman measurement of the temperature in active AIGaN/GaN. By varying the gate structure, the heat dissipation through the gate was clearly revealed. The temperature increased to 120 °C at the flat gate device although the inserted gate increased to only 37 °C. Our results showed that the inserted gate structure reduced the self-heating effect by three times compared to the flat gate structure. Temperature mapping using micro-Raman measurement confirmed that the temperature of the near gate area was lower than that of the near drain area. This indicated that the inserted gate electrode structure effectively prohibited self-heating effects.

A graphene-PbS quantum dot (QD) composite for application in high-performance near-infrared (NIR) photodetectors (PDs) is proposed in this study. A single-layer graphene flake and oleic acid-capped PbS QD composite is fabricated through the conventional sonication process, in hexane solution. Field emission scanning electron microscopy images of the graphene-PbS QD composite dispersed on a glass substrate confirm that the composite contains both aggregated graphene flakes and single-layer graphene with wrinkles; Transmission electron microscopy images reveal close packing with uniform size. The increased absorbance and quenched photoluminescence intensity of the graphene-PbS QD composite supports enhanced photoinduced charge transfer between graphene and the PbS QDs. Moreover, the specific Raman mode of the PbS QDs, embedded in the spectrum, is enhanced by combination with graphene, which can be interpreted by SERS as relevant to the photoinduced charge transfer between the Pbs QDs and graphene. For device application, a PD structure comprised by graphene-PbS QDs is fabricated. The photocurrent of the PD is measured using a conventional probe station with a 980-nm NIR laser diode. In the fabricated PD comprising graphene-PbS QDs, five-times higher photocurrent, 22% faster rise time, and 47% faster decay time are observed, compared to that comprising PbS QDs alone. This establishes the potential of the graphene-PbS QD composite for application in ultrathin, flexible, high-performance NIR PDs.

The fine control over the surface of lead sulfide colloidal quantum dots (PbS CQDs) is increasingly important to achieve enhanced device performance. In particular, the in-gap trap state resulting from the surface hydroxylation of PbS CQDs is considered detrimental to photovoltaic performance. In this study, we developed a method to avoid hydroxyl formation on the PbS CQD surface by using an in situ solution-phase ligand-exchange process. The complete elimination of protic solvents and other hydroxyl sources from the CQD synthesis to device fabrication produced PbS CQD films without undesired hydroxyl ligands with a reduced trap density. In this process, the purification process, which accounts for nearly 60% of the synthesis cost, is completely excluded. The presence of trap states verified through optical analysis and the hydroxylation observed via surface analysis clearly agreed with the device characterization obtained by transient photovoltage and photocurrent. Consequently, the open-circuit voltage of the PbS CQD solar cells is improved by up to 10%, yielding a certified power-conversion efficiency of 11.6%.

Solution-processed semiconductors are promising materials to realize optoelectronic devices that combine high performance with inexpensive manufacturing. In particular, the exploitation of colloidal quantum dots (CQDs) capable of harvesting infrared photons, in conjunction with visible-absorbing organic chromophores, has been demonstrated as an interesting route. Unfortunately, CQD/organic hybrid photovoltaics have been limited to power conversion efficiencies (PCEs) below 10% due to chemical mismatch and difficulties in facilitating charge collection. Here we devise a hybrid architecture that overcomes these limitations by introducing small molecules into the CQD/organic stacked structure. The small molecule complements CQD absorption and creates an exciton cascade with the host polymer, thus enabling efficient energy transfer and also promoting exciton dissociation at heterointerfaces. The resulting hybrid solar cells exhibit PCEs of 13.1% and retain over 80% of their initial PCE after 150 h of continuous operation unencapsulated, outperforming present air-processed solution-cast CQD/organic photovoltaics. Colloidal quantum dots and organics have complementary properties apt for photovoltaics, yet their combination has led to poor charge collection. Here, Baek et al. introduce small molecules that act as a bridge between quantum dots and polymers, thus improving device efficiency and stability.

Couette–Taylor flow reactor is a mixing device that offers wide range of mixing regimes within a single reactor and operates in continuous flow mode. This reactor is recently used in manufacturing the cathode material of lithium ion batteries. Here, we simulate the agglomeration process of Li(NixMnyCoz)O2 particles using computational fluid dynamics. Quadrature method of moments is implemented for modeling of aggregation and breakage in Couette-Taylor flow reactor. We conduct an experiment of the preparation of Li(NixMnyCoz)O2 precursors, and the experimental data are compared with simulated results for the validation of numerical model. The predicted evolutions of mean particle size are well agreed with experimental data. For the practical application, we investigate the effects of density ratio of particle to fluid and initial volume fraction of particles on the particle size. The results show that the particle diameter increases with increasing of density ratio, but it decreases with increasing of initial volume fraction of particles. On the other hand, the particle sizes become similar at high rotational speed.

Gallium oxide films were grown with nitrogen on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Nitrogen and oxygen gases supplied simultaneously through one plasma source were used to grow gallium oxide films with nitrogen. All the films had monoclinic β-Ga2O3 structure; however, their surface roughness increased with increasing nitrogen supply. The incorporation of nitrogen was confirmed by x-ray photoelectron spectroscopy. The average transmittance of the films was over 85% in the visible range and over 95% in the ultraviolet range. The as-deposited films had decreased bandgap energies from 4.92 eV to 4.35 eV, with increased nitrogen rate. That is, the bandgap energies of the gallium oxide films can be tuned simply by increasing nitrogen supply during their growth without any post-annealing process under nitrogen condition.

Ni-rich NCM-based cathode materials have garnered significant research interest for the development of high-performance lithium-ion batteries (LIBs) owing to their high energy capacity and low cost. However, they undergo several electrochemical degradation reactions that deteriorate the cathode performance. To alleviate the deterioration of the cathode, researchers have adopted surface coating materials, especially Li3BO3 (LBO), which demonstrates a superior modification effect, for Ni-rich NCM. Here, we investigate the electrochemical characteristics of an LBO-coated Ni-rich NCM cathode via experimental and numerical approaches. The cathode is synthesized through a wet chemical deposition method, and electrochemical measurements are conducted using coin half-cells. To further understand the effect of coating layer on the electrochemical performance, we developed an electrode coating model with modifying the porous electrode model. The model employs an impurity layer (Li2CO3 and LiOH), a protective layer (LiF), and a coating layer (LBO) to predict the discharge performance of LIBs. The validation results of the model are consistent with the experimental results. Electrochemical prediction results demonstrate that the LBO-coated Ni-rich NCM cathode would increase the discharge capacity.

The trap states and defects near the active region in deep-ultraviolet (DUV) light-emitting diodes (LED) were investigated through wavelength-dependent photocurrent spectroscopy. We observed anomalous photocurrent reversal and its temporal recovery in AlGaN-based DUV LEDs as the wavelength of illuminating light varied from DUV to visible. The wavelength-dependent photocurrent measurements were performed on 265 nm-emitting DUV LEDs under zero-bias conditions. Sharp near-band-edge (~265 nm) absorption was observed in addition to broad (300–800 nm) visible-range absorption peaks in the photocurrent spectrum, while the current direction of these two peaks were opposite to each other. In addition, the current direction of the photocurrent in the visible wavelength range was reversed when a certain forward bias was applied. This bias-induced current reversal displayed a slow recovery time (~6 h) when the applied forward voltage was removed. Furthermore, the recovery time showed strong temperature dependency and was faster as the sample temperature increased. This result can be consistently explained by the presence of hole traps at the electron-blocking layer and the band bending caused by piezoelectric polarization fields. The activation energy of the defect state was calculated to be 279 meV using the temperature dependency of the recovery time.

We investigated the distributions and the energy levels of defects in SiO2/AlGaN/GaN highelectron-mobility transistors (HEMTs) by using frequency-dependent (F-D) capacitance-voltage (C-V) measurements with resonant optical excitation. A Schottky barrier (SB) and a metal-oxidesemiconductor (MOS) HEMT were prepared to compare the effects of defects in their respective layers. We also investigated the effects of those layers on the threshold voltage (V th ). A drastic voltage shift in the C-V curve at higher frequencies was caused by the large number of defect levels in the SiO2/GaN interface. A significant shift in V th with additional light illumination was observed due to a charging of the defect states in the SiO2/GaN interface. The voltage shifts were attributed to the detrapping of defect states at the SiO2/GaN interface.

We have investigated poly (3-hexylthiophene) (P3HT) as a hole transport material interfacing PbS quantum dot and anode, and found that carrier separation is enhanced by increasing carrier concentration and mobility of P3HT. In addition, the ambient stability of PbS colloidal quantum dot solar cells are shown to be improved by surface oxidation of P3HT. Comparing with MoO3 anode interfacing material, P3HT performs better with controllable ambient stability. Electrode interfacing material should enable appropriate internal force for efficient carrier separation and enough carrier mobility to minimize carrier losses, which needs to provide a surface stabilization strategy to prevent degradation induced by ambient oxidation.

Growth of ZnSnN2 films on (0001) Al2O3 substrates is performed by plasma-assisted molecular-beam epitaxy by changing the growth temperatures from 350 to 650 °C. Single crystal ZnSnN2 films have been grown by using ZnO buffer while the film grown without the ZnO buffer has shown amorphous-like disordered characteristics addressed by no observation of any diffraction from reflection high-energy electron diffraction. All the grown crystalline ZnSnN2 films with ZnO buffer show a pseudowurtzite structure without the formation of an orthorhombic structure. Epitaxial relationships between Al2O3 substrate, ZnO buffer, and ZnSnN2 film are determined to be [1120] ZnSnN2//[1120] ZnO//[1010] Al2O3 and [0001] ZnSnN2//[0001] ZnO//[0001] Al2O3. The bandgaps of ZnSnN2 films could be tuned from 1.85 to 2.15 eV, simply by increasing the growth temperatures from 350 to 650 °C. The carrier concentrations and carrier mobilities were investigated and compared. Since the growth of single crystal ZnO films has been reported o...

Accurately predicting the peak wavelength and intensity of the electroluminescence spectrum through the photoluminescence method which can be measured without connecting electrodes is not only practically important for the development of micro-LEDs that cannot be fully inspected for device development, but there is also a fundamental importance in understanding the light emitting mechanism of the LEDs. In this study, the correlation and detailed mechanism between PL and EL are systematically analyzed by considering the effects of carrier escape, carrier accumulation, applied bias, leakage current, incident light wavelength and light absorption in order to provide a clear path for all-optical inspection of light emitting diodes and complete understanding of the luminescence mechanism in GaN-related quantum wells.

Organic-inorganic hybrid photovoltaics (PVs) have recently attracted considerable attention as their PV performance has rapidly improved. Abnormal current-voltage (I-V) characteristics or I-V hysteresis, however, were occasionally observed in such systems that hampered the development of the PV technology. Here we study the hysteresis of organic-inorganic hybrid colloidal quantum dot (CQD) PVs by analyzing I-V characteristics upon systematic modulation of organic components of CQDs. We demonstrate that an external bias stress to CQD films transiently prompts redistribution of mobile ions, particularly protons of surface ligands, thus leading to the formation of a transient space-charge region in the CQD films. The variable space-charge region causes I-V hysteresis and photoinstability of CQD PVs, which is closely correlated with the transient behavior of mobile ions. Our findings here could provide significant implications to the understanding of the influence of mobile ions on I-V hysteresis in other organic-inorganic hybrid PVs such as perovskites.

Plasma-assisted molecular beam epitaxy (PAMBE) was used to grow Ga2O3 films on oxidized GaN layers on nitrided sapphire substrates. The GaN layer was grown by PAMBE, and the in situ oxidation of the GaN layer was achieved through exposure to oxygen plasma, which resulted in the formation of monoclinic β-Ga2O3. Crystalline monoclinic β-Ga2O3 films were grown on the GaN layers, with and without oxidation. The orientation relationships were [\(11\overline{2} 0\)] Al2O3//[\(1\overline{1} 00\)] AlN//[\(1\overline{1} 00\)] GaN//[102] β-Ga2O3 and [\(1\overline{1} 00\)] Al2O3//[\(11\overline{2} 0\)] AlN//[\(11\overline{2} 0\)] GaN//[010] β-Ga2O3. The grown β-Ga2O3 films were not single-crystalline but showed rotational domains along the growth direction with three variations, which resulted in six-fold rotational symmetry instead of two-fold rotational symmetry. The surface roughness of the grown β-Ga2O3 film was closely reflected to that of as-grown GaN and oxidized GaN. By analyzing the x-ray omega rocking curves for the on-axis (\(\overline{2} 01\)) and off-axis (002) reflections, it was concluded that rotational domains dominantly affected the crystal quality of the β-Ga2O3 films.

We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with a chemical bath deposition (CBD)-ZnS buffer layer grown with varying ammonia concentrations in aqueous solution. The solar cell performance was degraded with increasing ammonia concentration, due to actively dissolved Zn atoms during CBD-ZnS precipitation. These formed interfacial defect states, such as hydroxide species in the CBD-ZnS film, and interstitial and antisite Zn defects at the p-n heterojunction. After light/UV soaking, the CIGS solar cell performance drastically improved, with a rise in fill factor. With the Zn-based buffer layer, the light soaking treatment containing blue photons induced a metastable state and enhanced the CIGS solar cell performance. To interpret this effect, we suggest a band structure model of the p-n heterojunction to explain the flow of photocarriers under white light at the initial state, and then after light/UV soaking. The determining factor is a p+ defect layer, containing an amount of deep acceptor traps, located near the CIGS surface. The p+ defect layer easily captures photoexcited electrons, and then when it becomes quasi-neutral, attracts photoexcited holes. This alters the barrier height and controls the photocurrent at the p-n junction, and fill factor values, determining the solar cell performance.

The effect of growth pressure on the morphology of the ZnO nanostructures in chemical vapor transport by using Zn powder and oxygen as source materials has been investigated. Highly uniform aligned ZnO nanorods or multifaceted tripod structures were grown depending on the growth pressure. The mechanism governing the morphology change was explained by the relative concentration of Zn vapor and supersaturation based on experimental observations. It was concluded that heterogeneous nucleation on the substrate is enhanced at low growth pressure, while homogeneous nucleation from vapor phase is enhanced at high growth pressure. The difference resulted in different morphology of ZnO nanostructures. ZnO nanorods grown at optimized condition were used for the fabrication of gas sensor for the detection of H 2 gas.

We fabricated a hole transport layer (HTL) using transfer printing to fabricate high efficiency PbS quantum dot solar cell with minimized hysteresis. We applied PbS-EDT(1,2-ethanedithiol) as an HTL and controlled the adhesive properties between the donor substrate and the HTL through the UVO process in order to effectively transfer the HTL to the PbS layer, which enabled multilayer transfer printing as a result. During the transfer printing process, a gradient solid-solution layer was created at the interface with the existing PbS layer to reduce the hysteresis phenomenon, and to improve the power conversion efficiency to about 10% according to the HTL thickness optimization. In addition, the use of the EDT solvent can be remarkably reduced by using the transfer printing when forming the PbS-EDT layer. This can reduce the amount of organic solvent consumed in the process and improve the potential of environmentally friendly processes.

In this report, we explore the underlying mechanisms by which doped organic thin films as a top hole-selective layer (HSL) improve the performance and stability of colloidal quantum dot (CQD)-based solar cells. Molecular dynamics-based theoretical studies prove that the hydro/oxo-phobic properties of the HSL serve to efficiently passivate the CQD solid. Furthermore, the robust and outstanding electrical properties of the HSL, simultaneously ensure a high power conversion efficiency (PCE) and increase the stability performance of CQD-based solar cells. As a result, a best PCE of 11.7% in a lead sulfide (PbS)-based CQD solar cell is achieved and over 90% of the initial performance is retained after 1 year storage under ambient conditions.

We investigated the properties of flexible InGaN LEDs fabricated on a 2-in. polyimide substrate with various radii of curvature R . The output power of the LEDs slightly increased as R decreased for a given input current. The output power decreased and surface cracks appeared in the curved devices at currents larger than a critical current, although this current was smaller for devices with a smaller R . Reverse-biased electro-reflectance spectroscopy revealed that both the compressive strain in the InGaN layers and the related piezoelectric field increased as R decreased.

We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with chemical-bath deposited (CBD) ZnS buffer layers with different deposition times. The conversion efficiency and the fill factor of the CIGS solar cells reveal a strong dependence on the deposition time of CBD-ZnS films. In order to understand the detailed relationship between the heterojunction structure and the electronic properties of CIGS solar cells with different deposition times of CBD-ZnS films, capacitance–voltage (C–V) profiling measurements with additional laser illumination were performed. The light-soaking effects on CIGS solar cells with a CBD-ZnS buffer layer were investigated in detail using current density–voltage (J–V) and C–V measurements with several different lasers with different emission wavelengths. After light-soaking, the conversion efficiency changed significantly and the double diode feature in J–V curves disappeared. We explain that the major reason for the improvement of efficiency by light-soaking is due to the fact that negatively charged and highly defective vacancies in the CIGS absorber near the interface of CBD-ZnS/CIGS were formed and became neutral due to carriers generated by ultra-violet absorption in the buffer layer.

A new configuration of a plasmonic quantum dots solar structure is proposed. Gold-silver core-shell metal nanoparticles (Au@Ag NCs) are incorporated into the TiO2 layer (Au@Ag NCs-HL) of PbS-based solar cells. The TiO2 layer enables the Au@Ag NCs to have broad plasmonic responses and the external quantum efficiency and absorption of the plasmonic devices are significantly enhanced. The electrical performance of the solar cells is also improved.

Using a combination of quantum dots (QDs) of different sizes, and thus different bandgaps, to extend the light-harvesting spectrum of a photovoltaic device in tandem architecture is a promising strategy for increasing the solar cell efficiency. In this study, we propose a new architecture for a solar cell device consisting of a graded-bandgap active layer made of lead sulfide QDs of different sizes and based on the structure of the Schottky junction. Colloidal PbS QDs with bandgaps of 1.55, 1.44, and 1.36 eV were synthesized and used to construct a series of Schottky junction solar cells. Cells with a graded-bandgap active layer exhibited an increase in short-circuit current density (Jsc) but yielded lower open-circuit voltage (Voc) compared with cells having a uniform bandgap. We found that adding a thin electron energy-boosting layer (EEB) made from 1.55-eV-bandgap QDs can partially compensate for the thermalization loss, and thus enhance Jsc and recover Voc. Consequently, this study provides a conceptual basis for further improvement in colloidal QD-based solar cells.

The effect of electron blocking layer (EBL) on the injection and radiative efficiencies in InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) was investigated. In order to identify the dominant mechanism, we measured the external quantum efficiency (EQE), radiative efficiency (RE) and carrier injection efficiency (CIE) experimentally. Through these methods, the origin of efficiency droop and the effect of the EBL were clarified. In addition, the RE and the CIE can be separated quantitatively through our analysis. The insertion of the EBL does reduce the carrier leakage but the RE is also reduced by the insertion, which results in not a significant change in the EQE. The measured piezoelectric field of the QWs significantly increased by the insertion of the EBL, which implies that the insertion of AlGaN layer make a strong effect on the QW strain.

We analyzed the current-crowding process and its effects on carrier spill-over and light outputpower loss in InGaN/GaN blue-light-emitting diodes. When the current density was measured to be 3.1 times larger, the carrier spill-over was observed to be 1.9 times higher. The effects of current crowding on the loss of efficiency and on carrier spill-over were determined quantitatively. Through this analysis, we were able to correlate the degree of current crowding with the loss rate of lightoutput power. When the injected current was increased 2.5 times, the current-spreading length decreased 1.2 times, and the loss rate of the light-output power increased from 5% to 12%.

The PbS quantum dot is an emerging photovoltaic material, which may provide high efficiency breakthroughs. The most crucial element for the high efficiency solar cells's development is to understand charge transport characteristics of PbS quantum dot solids, which are also important in planning strategic research. We have investigated charge transport characteristics of PbS quantum dot solids thin films using space charge limited conduction analysis and assessed thickness dependent photovoltaic performances. The extracted carrier drift mobility was $low-10^{-2}cm^2/Vs$ with the estimated diffusion length about 50 nm. These and recently reported values were compared with those from a commercial photovoltaic material, and we present an essential element in further development of PbS quantum dot solids materials.

Typically, three kinds of ZnO nanostructures, nanowires, nanosheets, and nanorods, are synthesized by changing the reactor pressure in the chemical vapor transport method. The photoelectrochemical (PEC) properties of ZnO nanostructures were investigated by using an ultraviolet lamp with a wavelength of 365 nm and a measured intensity of 0.4 mW/cm22. Photocurrent densities of 0.61, 0.47, and 0.37 mA/cm2 were obtained for nanowires, nanosheets, and nanorods, respectively. The photoconversion efficiencies of these ZnO nanostructures under ultraviolet illumination were calculated as 73.1, 57.3, and 41.8%, respectively. The different PEC results were explained by using the effects of dimension in the nanostructures. The separation of light-induced charge formed near the surface, leading to the transfer of electron holes toward the surface and electrons toward the bulk at the photo-anode, will be higher as the dimension is decreased. The difference in the optical absorption in the PEC process could be neglected because the absorption intensities were nearly the same for the three kinds of samples, independent of both the morphology and the density. Therefore, the different PEC efficiencies could be thought to be a result of the difference in the nanostructures with different dimensions, not the result of the density of the nanostructure.

We report on the structural and optical properties of non polar a-plane MgxZn1−xO (0 ⩽ x ⩽ 0.57) films on r-plane sapphire substrates grown by plasma-assisted molecular beam epitaxy. Reflection high energy electron diffraction (RHEED) revealed a formation of cubic MgO phase when an Mg concentration increases. Room temperature (RT) photoluminescence (PL) and transmission electron microscopy consistently revealed the formation of cubic MgO phase from the Mg0.21Zn0.79O film. The Mg0.11Zn0.89O film showed a band edge emission at ∼360 nm, which is a shorter wavelength than the ZnO (∼373 nm), from the RT PL measurements. Photoluminescence excitation (PLE) measurements at RT showed that band-gap energies of MgxZn1−xO films could be tuned up to ∼4.65 eV (∼270 nm) although cubic MgO phase were mixed for high Mg concentration. For the single phase wurtzite MgZnO film, band-gap energy of 3.48 eV was obtained from the Mg0.11Zn0.89O film.

A rapid increase in power conversion efficiencies in colloidal quantum dot (QD) solar cells has been achieved recently with lead sulphide (PbS) QDs by adapting a heterojunction architecture, which consists of small-area devices associated with a vacuum-deposited buffer layer with metal electrodes. The preparation of QD solar modules by low-cost solution processes is required to further increase the power-to-cost ratio. Herein we demonstrate all-solution-processed flexible PbS QD solar modules with a layer-by-layer architecture comprising polyethylene terephthalate (PET) substrate/indium tin oxide (ITO)/titanium oxide (TiO2)/PbS QD/poly(3-hexylthiophene) (P3HT)/poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS)/Ag, with an active area of up to 30 cm(2), exhibiting a power conversion efficiency (PCE) of 1.3% under AM 1.5 conditions (PCE of 2.2% for a 1 cm(2) unit cell). Our approach affords trade-offs between power and the active area of the photovoltaic devices, which results in a low-cost power source, and which is scalable to larger areas.