Search

In this study, we investigated the effect of the stacking order of metal precursors on the formation of volume defects, such as blisters and nanopores, in CZTSSe thin-film solar cells. We fabricated CZTSSe thin films using three types of metal-precursor combinations, namely, Zn/Cu/Sn/Mo, Cu/Zn/Sn/Mo, and Sn/Cu/Zn/Mo, and studied the blister formation. The blister-formation mechanism was based on the delamination model, taking into consideration the compressive stress and adhesion properties. A compressive stress could be induced during the preferential formation of a ZnSSe shell. Under this stress, the adhesion between the ZnSSe film and the Mo substrate could be maintained by the surface tension of a metallic liquid phase with good wettability, or by the functioning of ZnSSe pillars as anchors, depending on the type of metal precursor used. Additionally, the nanopore formation near the back-contact side was found to be induced by the columnar microstructure of the metal precursor with the Cu/Zn/Mo stacking order and its dezincification. Based on the two volume-defect-formation mechanisms proposed herein, further development of volume-defect-formation suppression technology is expected to be made.

Cesium lead bromide (CsPbBr3), an inorganic perovskite material with a large band gap energy (Eg = 2.3 eV), is a great candidate to produce stable and semitransparent perovskite solar cell (PSC) pl...

Inorganic perovskite solar cells (PSCs) are considered prospective alternatives to organic PSCs due to their efficiency and relative stability. Cesium lead bromide (CsPbBr3) has a complete perovskite structure, is phase stable, exhibits a wide bandgap energy of 2.3 eV under operating conditions, and is regarded as a suitable material not only for stable PSCs, but also for semi-transparent PSCs. In this study, we synthesize Cu–Zn–In–S–Se (CZISSe) quantum dots (QDs) and demonstrate their novel use for improving the performance of PSC devices. QDs are embedded through ligand-exchange, which replaces long organic chains with thiosulfate (–S2O3) ligands and disperses the S2O3-capped QDs in the PbBr2 solution to prepare QD-blended precursor inks. The QDs promote the crystallization of CsPbBr3 and hole extraction from the photoactive layer. As a result, the optimized power conversion efficiency (PCE) of the QD-incorporated PSC is 5.37%, which is a 22.6% enhancement compared to those of the control devices. This work provides an effective and simple process for enhancing the performance of CsPbBr3-based PSCs.

In this study, we investigated the electrical and structural properties of sulfur-graded Cu2ZnSn(S,Se)4 (CZTSSe) thin films grown using a modified two-step process according to the annealing temperature. The sulfur content of the CZTSSe thin film was increased with annealing temperature and a Zn(S, Se) secondary phase was observed at temperatures higher than 500 °C. The Raman spectrum of the CZTSSe thin film shifted continuously toward the high frequency direction with increasing S content and the Cu2SnSe3 (CTSe) secondary phase was present below 440 °C. From the results of dimpling Raman spectroscopy and scanning transmission electron microscopy (STEM) line scanning, we confirmed that the S content increased gradually from the Mo back contact to the surface of the CZTSSe thin film. Finally, a sulfur-graded CZTSSe thin film with a photovoltaic efficiency of 7.03% was fabricated by optimizing the annealing temperature.

In this study, the application of Sb incorporation for low-temperature (≤ 450 °C) processing of Cu(In,Ga)Se2 (CIGSe) solar cells is explored. At low reaction temperature, most Ga remains at the back of the film adjacent to the Mo back contact. We observed that the incorporated Sb enhanced grain size and improved device performance compared with similarly processed CIGSe films made without Sb. From the energy-dispersive spectroscopy analysis and secondary ion mass spectrometry results, it was determined that elemental Ga accumulation at the back of the reacted film after the two-step selenization process was significantly alleviated owing to Sb incorporation. Significant Sb-induced grain size enhancement was confirmed using cross-sectional scanning electron microscopy. The electronic and optical properties of the Sb incorporated CIGSe films were examined with admittance spectroscopy and fluorescence lifetime imaging techniques.

In recent years, Cu2ZnSn(S1-xSex)4 (CZTSSe) prepared by a two-step process using metal precursors has been reported to exhibit a relatively high power conversion efficiency, and a high efficiency of 12.5% by two-step process contained via sputtering method was recently confirmed by our group. In this study, we proposed formation mechanisms for the CZTSSe double layer, voids and ZnSSe layer, which were observed in the CZTSSe using metal precursor. Due to the persistent dezincification from the metal precursors and preferential reaction between the Zn and chalcogens such as S and Se, almost all Zn is consumed to form the ZnSSe layer; as a result, large voids are produced first under the ZnSSe layer. Cu2Se and SnSe are grown on the ZnSSe layer via migration of the Cu and Sn through the grain boundaries of the ZnSSe layer. Thus, additional small voids are expected to form due to the mass transfer of Cu and Sn. Because of the preferentially formed ZnSSe layer and the chalcogenation of Cu and Sn after the mass transfer, a CZTSSe double layer can be formed, and ZnSSe can exist between these CZTSSe layers. Finally, we propose a method based on the formation mechanism to control the voids and secondary phases, which affect the fill factor and output current.

We fabricated CZTSSe thin films using optimized SLG-Mo/Zn/Cu/Sn (MZCT) as a stacked structure and described the phenomenon of Zn elemental volatilization using the MZCT stacked structure. We introduced H2S gas to effectively control the S/(S + Se) ratio of the film in the sulfo-selenization process and to suppress Zn volatilization. Unlike during the selenization process, a stable ZnSSe thin film was formed on the precursor surface during the sulfo-selenization process. The formation of the ZnSSe thin film inhibited Zn volatilization, which facilitated control of the thin film stoichiometry and played an important role in crystal growth. In addition, the sulfo-selenization process using H2S forms a grading of the S/(S + Se) ratio in the depth direction in the ZnSSe layer. The ZnSSe layer with this property causes the band gap grading in the CZTSSe absorption layer. Finally, through our optimized annealing process, we realized a world record CZTSSe solar cell with a certified power conversion efficiency of 12.62% and a centimetre-scale (1.1761 cm2) efficiency of 11.28%.

We fabricate bifacial Cu2ZnSnSe4 (CZTSe) thin-film solar cells on indium tin oxide (ITO) substrates using a vacuum procedure. We find that, as the annealing temperature increases from 500 to 540 °C, the performance of the CZTSe solar cell rapidly degrades due to Sn–In diffusion. We implement Mo interlayers at the CZTSe absorber/ITO interface to suppress this Sn–In movement. During annealing, the selenized Mo interlayer with MoSe2 effectively acts as a barrier layer to reduce the In diffusion into the CZTSe absorber. The relationship between the Mo thickness and the CZTSe performance is addressed. Because the Mo interlayer is used, the conversion efficiency of the CZTSe solar cells greatly improves, from 0.40% to 5.21% under front illumination. Also, the effects of the bifacial conditions and Mo interlayer thickness on the performance of the CZTSe solar cells are investigated. Under bifacial illumination (front: 1.0 sun/rear: 0.3 sun), the conversion efficiency of the CZTSe solar cells increases by up to 10% compared with that under front illumination only, achieving a value of 5.71% for CZTSe/ITO.

The Ag nanowire (NW) + Au nanoparticle (NP)-embedded TiO2 photoelectrodes were adopted for conventional planar TiO2-based Sb2S3 hybrid solar cells to improve the cell efficiency. Compared to conventional planar TiO2-based Sb2S3 hybrid solar cells, the Ag NW + Au NP/TiO2-based Sb2S3 hybrid solar cells exhibited an improvement of approximately 40% in the cell efficiency due to the significant increase in both Jsc and Voc. These enhanced Jsc and Voc were attributed to the increased surface area, charge-collection efficiency, and light absorption by embedding the Ag NWs + Au NPs composite. The Ag NW + Au NP/TiO2-based Sb2S3 hybrid solar cells showed the highest efficiency of 2.17%, demonstrating that the Ag NW + Au NP-embedded TiO2 photoelectrode was a suitable photoelectrode structure to improve the power conversion efficiency in the Sb2S3 hybrid solar cells.

In traditional dye-sensitized solar cells (DSSCs), the liquid electrolyte (LE) presents a problem for long-term stability. Herein, we demonstrate a bifacial DSSC by combining a new metal-free organic dye and a quasi-solid state electrolyte (QSSE) that contains poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)-based polymer gel. The incident light irradiates the front side of the DSSC, and the transmitted light is reused after reflection on the back side. Owing to the semi-transparent DSSC electrode, the reflected light can penetrate and be absorbed by the dye molecules in the DSSC, thereby enhancing the short-circuit current density and thus the overall power conversion efficiency (PCE). The PCE for the DSSC device with QSSE from bifacial irradiation is 10.37%, a value that is comparable to that obtained with LE-based DSSC (9.89%). The stability of the device is enhanced when the polymer gel containing PVdF-HFP is mixed with the LE, and the effectiveness of PVdF-HFP as a gelator is attributed to its interaction with the Li+ ions. Based on our preliminary results, this architecture can lead to more stable bifacial QSSE-based DSSCs without sacrificing the photovoltaic performance.

In this study, we investigate the electrical, structural, and optical properties of band gap front-graded Cu2ZnSn(S,Se)4 (CZTSSe) thin films grown by a modified single-step sulfo-selenization process from copper-poor and zinc-rich precursor metallic stacks prepared by co-evaporation. To investigate how the bandgap was graded in connection with the compositional distribution, we calculated the bandgap energy distribution along the film thickness, based on the transmission electron microscopy and energy-dispersive X-ray spectroscopy composition profile. The band gap of the CZTSSe phase with high S content near the surface layer is determined to be 1.161 eV. From the surface to the bottom, there is a decrease in the S content of the CZTSSe phase, and the band gap subsequently decreases to, 1.029 eV, close to the value of CZTSe. From the results of dimpling-Raman and scanning transmission electron microscopy line scanning, we confirm that the S content drastically increases from the bottom to the top surface of the CZTSSe thin film. The CZTSSe thin-film solar cell exhibits a power conversion efficiency (PCE) of 10.33%, with an open-circuit voltage (Voc) of 0.505 V, short-circuit current density (Jsc) of 31.61 mA/cm2, fill factor (FF) of 64.6%, and Voc deficit of 525 mV. Compared with the performance of the CZTSe solar cell, which had PCE of 7.23%, Voc of 0.424 V, Jsc of 32.83 mA cm−2, FF of 51.9%, and Voc deficit of 576 mV, the Voc and Voc deficit of the CZTSSe cell improved considerably. The high Voc, low Voc deficit, and less loss of Jsc are attributed to the effect of band gap front-grading induced by S grading into the CZTSSe thin film.

We investigated an electrospray-based method to manufacture photoelectrodes for dye-sensitized solar cells (DSSCs). TiO2 doughnut-, spherical-, and disk-shaped particles with a large surface area, high crystallinity, uniform nanostructure, and good light scattering properties were fabricated via a simple electrospray method. The control of the morphology of the nanostructured particles prepared by electrospraying a dispersion of nanoparticles was investigated experimentally; the results are qualitatively explained on the basis of the available theory. The solvent in the droplet, droplet size, surface tension, process temperature, and process humidity are crucial to the morphology of the resulting particles. The effect of the particle morphology on the performance of DSSCs is demonstrated. Compared to the DSSCs with conventional photoelectrodes (with a power conversion efficiency of 8.4%), the DSSCs based on doughnut-, spherical-, and disk-shaped particle photoelectrodes yielded higher power conversion efficiencies of 8.8%, 9.3%, and 10.4%, respectively. The DSSC utilizing the disk-type photoelectrode showed the best performance under AM1.5 global illumination through a photo-mask at an illumination power of 100 mW cm−2. This is because the generated TiO2 disks provide a large surface area and exhibit excellent light scattering capabilities, thus resulting in a low total internal resistance and long electron lifetime.

In this study, we investigate methods of improving the efficiency of Cu 2 ZnSn(S,Se) 4 (CZTS)-based solar cells by comparing Cu(In,Ga)Se 2 (CIGSe)- and CZTS-based absorber layers. In particular, the CZTS-based absorber exhibits lower current characteristics than the CIGSe absorber layer in terms of the band gap alignment and electron-hole recombination at the CdS-absorber interface. Moreover, we demonstrate that defects are one of the causes of the voltage loss. In order to improve the efficiency of CZTS-based solar cells, it is important to control the band gap alignment at the CdS-absorber layer interface and to suppress the formation of secondary phases inside the absorber.

We evaluated a ZnS buffer layer prepared using a chemical bath deposition (CBD) process for application in cadmium-free Cu(In,Ga)Se2 (CIGS) solar cells. The ZnS buffer layer showed good transmittance (above 90%) in the spectral range from 300 to 800 nm and was non-toxic compared with the CdS buffer layers normally used in CIGS solar cells. The CBD process was affected by several deposition conditions. The deposition rate was dependent on the ammonia concentration (complexing agent). When the ammonia concentration was either too high or low, a decrease in the deposition rate was observed. In addition, post heat treatments at high temperatures had detrimental influences on the ZnS buffer layers because portions of the ZnS thin films were transformed into ZnO. With optimized deposition conditions, a CIGS solar cell with a ZnS buffer layer showed an efficiency of 14.18% with a 0.23 cm2 active area under 100 mW/cm2 illumination.

Although Cu2ZnSn(S,Se)4 (CZTSSe) has attracted attention as an alternative to CuInGaSe2 (CIGS) as an absorber material in solar cells, its low efficiency is a serious shortcoming preventing its commercialization. To realize a high-efficiency CZTSSe solar cell, improved grain crystallinity, inhibited secondary-phase formation, controlled defect generation, adequate Na content, and band gap grading are required in the absorber layer. Few studies have focused specifically on band gap grading. In this study, a method of using SeS2, a new potential chalcogenization source material, to control the S and Se contents in a CZTSSe absorber and its effects were investigated. Using an appropriate SeS2/Se weight ratio, band gap grading was realized within the depletion region. By increasing the value of VOC through band gap grading in the depletion region, a record VOC deficit of 0.576 V was achieved. Furthermore, the possibility of enhancing JSC through the formation of a type-inverted n-type phase at the absorber surface in response to an appropriate alignment of the conduction-band minimum energy level and the Fermi energy pinning level is discussed. By introducing the chalcogenization source material SeS2 during the annealing process, CZTSSe solar cells with a maximum efficiency of 12.3% were obtained.

To meet the nanofabrication requirements, such as control of structure and scalability, we investigated an electrospray-based method to manufacture scattering layers (SLs) for dye-sensitized solar cells (DSSCs). TiO2 spherical and disk-shaped particles with a large surface area, high crystallinity, uniform nanostructure and good light scattering properties were fabricated via a simple electrospray method. We showed how the morphology and structure of the resulting films can be controlled by varying the droplet evaporation rates before impact on the substrate. Thus, by tuning the process conditions, high-quality TiO2 spheres and disks were obtained. Then, these mesoporous TiO2 particles were used as the SLs in photoelectrodes, which resulted in enhanced power conversion efficiency (PCE). Compared with conventional SLs (8.45%), DSSCs based on spherical and disk-shaped particle SLs yield higher PCEs of 9.0% and 9.53%, respectively. This is because the generated TiO2 spheres and disks provide a large surface area and exhibit excellent light scattering capabilities, allowing a low total internal resistance and a long electron lifetime.

The Ag nanowire (NW) + Au nanoparticle (NP)-embedded TiO2 photoelectrodes were adopted for conventional planar TiO2-based Sb2S3 hybrid solar cells to improve the cell efficiency. Compared to conventional planar TiO2-based Sb2S3 hybrid solar cells, the Ag NW + Au NP/TiO2-based Sb2S3 hybrid solar cells exhibited an improvement of approximately 40% in the cell efficiency due to the significant increase in both Jsc and Voc. These enhanced Jsc and Voc were attributed to the increased surface area, charge-collection efficiency, and light absorption by embedding the Ag NWs + Au NPs composite. The Ag NW + Au NP/TiO2-based Sb2S3 hybrid solar cells showed the highest efficiency of 2.17%, demonstrating that the Ag NW + Au NP-embedded TiO2 photoelectrode was a suitable photoelectrode structure to improve the power conversion efficiency in the Sb2S3 hybrid solar cells.

Sub-micron thick Cu(In,Ga)Se2 (CIGS) thin films were deposited on Mo-coated soda-lime glass substrates under various conditions by single-stage co-evaporation. Generally, the short circuit current (Jsc) decreased with the decreasing thickness of the absorber layer. However, in this study, Jsc was nearly unchanged with decreasing thickness, while the open circuit voltage (Voc) and fill factor (FF) decreased by 31.9 and 31.1%, respectively. We believe that the remarkable change of Voc and FF can be attributed to the difference in the total amount of injected thermal energy. Using scanning electron microscopy, we confirmed that the surface morphology becomes smooth and the grain size increased after the annealing process. In the X-ray diffraction patterns, the CIGS thin film also showed an improved crystal quality. We observed that the electric properties were improved by the in-situ annealing of CIGS thin films. The reverse saturation current density of the annealed CIGS solar cell was 100 times smaller than that of reference solar cell. Thus, sub-micron CIGS thin films annealed under a constant Se rate showed a 64.7% improvement in efficiency.

In this study, we investigated the electrical, structural, and optical properties of Al-doped ZnO (AZO) thin films approximately 50 nm thick grown by atomic layer deposition (ALD) on glass substrates at 200 °C. An H2O pretreatment was conducted for all AZO samples. The electrical properties of the AZO thin film were improved after the pretreatment process. The Al doping concentrations were controlled by inserting an Al2O3 cycle after every "n" ZnO cycles while varying n from 99 to 16. As the doping concentration increases, the resistivity decreases and the optical band gap increases. When the Al2O3 cycle ratio is 5%, the electrical resistivity showed the lowest value of 4.66 x 10(-3) Ω cm. A carrier concentration of 1.10 x 10(20) cm(-3), and the optical transmittance exceeding 90% were obtained in the visible and near-infrared region. The thin film was strongly textured along the (100) direction in the X-ray diffraction patterns.

A nanoparticle-based DSSC shows limited efficiency levels due to its disordered geometrical structure and interfacial interference during electron transport, whereas the use of nanofibers in a DSSC can increase the electron mobility at the interfacial area of the materials due to the reduced recombination of electrons before reaching the collecting electrode. In this study, we describe the fabrication and characteristics of a ZnO nanofiber electrode for DSSC. From the results of a thermogravimetric analysis, a stepped heat treatment was developed for the calcinations of the ZnO electrodes. The ZnO electrode morphology and crystalline structure were confirmed by scanning electron microscopy and the X-ray diffraction patterns, respectively. The DSSC with the ZnO nanofiber photoelectrode (wire shaped) created by electrospinning showed an enhanced short-circuit current density (37% enhancement) compared to that of a ZnO sphere particle-shaped photoelectrode under irradiation of AM 1.5 simulated sunlight (100 mW/cm2). Moreover, we have investigated the origin of the improved performance through electrochemical impedance spectroscopic (EIS) and open-circuit voltage-decay (OCVD) measurements.

A mesoporous TiO2 photo-electrode for dye-sensitized solar cells (DSSCs) was fabricated by an electrospray method using a solution of dispersed TiO2 nanocrystals (P25). A mesoporous TiO2 disk has a larger surface area than P25. The sub micrometer-sized TiO2 disk promotes light scattering, thereby increasing the photocurrent conversion efficiency. However, the electrosprayed TiO2 electrodes have many pores and disconnected electron pathways. Thus, we investigated the enhanced electrical contact of an electrosprayed TiO2 electrode using a hot-pressing process and a titanium tetrachloride (TiCl4) treatment process. After optimizing the post-treatment process of an electrosprayed TiO2 electrode, the cell shows conversion efficiency up to 6% at standard sunlight of AM 1.5.

In this paper, we have studied the effect of the thickness of a CH3NH3PbI3 perovskite overlayer on mesoporous TiO2 electrodes in perovskite solar cells. The overlayers were prepared by spin coating PbI2 films on the electrodes, which were subsequently exposed to a CH3NH3I/2-propanol solution. We controlled the thickness of the perovskite overlayer by changing the PbI2 solution concentration. The thicknesses of the overlayers spin-coated from 0.5, 0.75, 0.9, and 1 M PbI2 solutions were approximately 179, 262, 316, and 341 nm, respectively. Perovskite solar cells with an approximately 316-nm-thick overlayer showed the highest efficiency of 9.11%. We conclude that optimization of the perovskite overlayer thickness in the solar cell structure is necessary to improve the cell efficiency.

Cu2ZnSnS4 (CZTS)-based materials have a useful band gap and a high absorption coefficient; however, their power conversion efficiency is low compared with that of CdTe and Cu(In,Ga)Se2-based solar cells. Two of the factors that strongly affect CZTS solar cell characteristics are the MoS2 layer and the presence of defects. In this study, Mo back-contact layers were annealed to control MoS2 layer formation and the Na content in the Mo layer before the absorber precursor layer was deposited. The increase in oxygen content in the Mo layer suppressed MoS2 layer formation. In addition, the increase in Na diffusion during the initial stage of the absorber precursor deposition decreased the defect density in the absorber layer and in the absorber–buffer interface. These results were verified through measurements of the external quantum efficiency, the temperature dependence of the open-circuit voltage (VOC), and admittance spectra. The current densities (JSC) and VOC, as well as the power conversion efficiencies, improved as the annealing temperature of the Mo layer increased, which suggests that CZTS solar cell characteristics can be improved by suppressing MoS2 layer formation and increasing Na content in the Mo layer before deposition of the absorber precursor layer. Copyright © 2014 John Wiley & Sons, Ltd.

We have investigated the optical properties of CuIn1−xGaxSe2 (CIGS) thin film solar cells using their electroreflectance (ER) at room temperature. The ER spectra exhibited one broad and two narrow signal regions. Using the photoluminescence (PL) and photocurrent (PC) spectra, the peaks in the low-energy region (1.02–1.35 eV) can be assigned to the CIGS thin film. The PC results implied that the peaks in the high-energy region (2.10–2.52 eV) can be assigned to the CdS band-gap energy. Using the applied bias voltage, the broad signals in the 1.35–2.09 eV region can be assigned to the Franz–Keldysh oscillation (FKO) due to the internal electric field. The ER spectra exhibited a distorted CdS signal for the CIGS thin film solar cell with low shunt resistance and efficiency.

We have studied the effect of TiCl4 post-treatment on the embedded-type TiO2 nanotubes (NT)-dyesensitized solar cells (DSSCs). The TiO2 nanoparticles layer formed on TiO2 NTs surface by TiCl4 post-treatment showed different morphologies depending on TiCl4 treatment temperature. These different morphologies influenced the cell efficiency of TiO2 NT-DSSCs. The TiO2 NT treated with TiCl4 at 50 °C exhibited a rougher surface than that treated at 70 °C. The rough surface of the TiO2 NT improved the charge exchange between the dye and electrolyte. The TiO2 NT treated with TiCl4 at 50 °C showed better fill factor and cell efficiency than that treated at 70 °C. The TiCl4 post-treatment of TiO2 NT was effective at conditions of low temperature and long times. The TiO2 NT-DSSCs with TiCl4 post-treatment at 50 °C for 1.5 h showed an efficiency of 6.52%.

We have embedded a TiO2 nanoparticle (NP) photoelectrode in a Ti substrate to improve the cell efficiency of conventional TiO2 NP based dye-sensitized solar cells (DSSCs) using Ti substrate. Compared to the conventional standing-type (TiO2 NPs on Ti substrate) DSSCs, the embedded-type (TiO2 NPs embedded in Ti substrate) DSSCs have shown an approximately 35% improvement in power conversion efficiency due to the improvement of J(sc). The embedded-type DSSCs have more charge transport paths than do standing-type DSSCs due to the increase of contact area between the TiO2 NP sidewall and the Ti substrate. This increased contact area decreases the electrical resistance and increases the charge collection efficiency, which leads to the improvement of J(sc). The embedded-type NP-DSSCs are very effective DSSC structures for enhancing the power conversion efficiency of Ti substrate based DSSCs.

Light harvesting efficiency plays an important role in improving the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). Many researchers have employed a scatter layer to improve the light harvesting efficiency of DSSCs. In this paper, we propose a different DSSC structure that employs a patterned reflection layer to enhance the light harvesting efficiency and improve the PCE by reusing reflected light. Optical simulation data were collected through an optical analysis according to various patterns of the reflection layer. The optical simulation results revealed that the light harvesting efficiency of a rectangular patterned reflection layer was higher than that of other patterns. We evaluated the cell efficiency with current density–voltage characteristic curves by a solar simulator. The DSSC structures with a rectangular patterned reflection layer exhibited higher current densities and higher PCE values (22% enhancement) than those of traditional DSSCs, because light that passed through the photoanode was reflected, thereby making it possible to reuse it.

Nonpolar, a-plane 11 2 ¯ 0 ZnO thin films were epitaxially grown on r-plane 1 1 ¯ 02 sapphire substrate by radio frequency magnetron sputtering. The influence of oxygen partial pressure was studied. With increasing O 2 partial pressure of the Ar/O 2 sputtering gas, the ridge-like facet structure of the ZnO film altered to a smooth film. Full width half maximum of X-ray rocking curves for the on-axis 11 2 ¯ 0 reflections were 0.45°, 0.36°, 0.09° and 0.25° for samples grown at Ar/O 2 ratios of 2/1, 1/1, 1/2 and 1/3, respectively. A smooth surface could be obtained under oxygen rich conditions (Ar/O 2 ratio: 1/2), enhancing the lateral growth along the c-axis direction.

In this study, we have investigated the electrical and structural properties of sub-micron thick Cu(In,Ga)Se2 (CIGS) films with various in-situ post annealing times. Sub-micron thick CIGS films were deposited on Mo/soda-lime glass (SLG) substrates by single-stage co-evaporation. We decreased the deposition time to 700 s for sub-micron thick CIGS films (≈0.85 μm thickness). After deposition, the CIGS films were annealed under a constant Se rate by a SiC heater for 500–3000 s in a co-evaporator. Increased annealing time led to improved surface morphology and grain size. In the XRD patterns, the CIGS films also showed improved crystal quality for the (112) plane. We suggest that post annealing of sub-micron thick CIGS films at optimized time can be applied for improving device efficiency. The open circuit voltage (Voc) and the fill factor (FF) were increased by 15% and 10%, respectively. The total cell efficiency was increased by more than 35%.

We have proposed dye-sensitized solar cells (DSSCs) with trench-type TiO 2 nanotube structure to improve the low device efficiency of conventional TiO 2 nanotube DSSCs using Ti substrate. Compared to the conventional standing-type TiO 2 nanotube structure based DSSCs, the trench-type TiO 2 nanotube structure based DSSCs have shown an improvement of device efficiency of approximately 40% due to the large increase of Jsc. In the trench-type TiO 2 nanotube structure, the contact area between the TiO 2 nanotube sidewall and the Ti substrate is significantly increased. This increase of contact area provides more charge transport paths than exist in the conventional standing-type TiO 2 nanotube structure and reduces the electrical resistance between the Ti substrate and the TiO 2 nanotubes. Therefore, the remarkable increase of Jsc is the result of the charge collection efficiency, which is improved due to the increase of contact area between the TiO 2 nanotube sidewall and the Ti substrate in the trench-type TiO 2 nanotube structure. The fabrication of the trench-type TiO 2 nanotube structure is an effective manufacturing process for improving the device efficiency of TiO 2 nanotube based DSSCs using Ti substrate. DSSCs having an 11.9 μm thick trench-type TiO 2 nanotube structure have shown an efficiency of 5.74%.

To meet the nanofabrication requirements, such as control of structure and scalability, we investigated an electrospray-based method to manufacture scattering layers (SLs) for dye-sensitized solar cells (DSSCs). TiO

We evaluated a ZnS buffer layer prepared using a chemical bath deposition (CBD) process for application in cadmium-free Cu(In,Ga)Se2 (CIGS) solar cells. The ZnS buffer layer showed good transmittance (above 90%) in the spectral range from 300 to 800 nm and was non-toxic compared with the CdS buffer layers normally used in CIGS solar cells. The CBD process was affected by several deposition conditions. The deposition rate was dependent on the ammonia concentration (complexing agent). When the ammonia concentration was either too high or low, a decrease in the deposition rate was observed. In addition, post heat treatments at high temperatures had detrimental influences on the ZnS buffer layers because portions of the ZnS thin films were transformed into ZnO. With optimized deposition conditions, a CIGS solar cell with a ZnS buffer layer showed an efficiency of 14.18% with a 0.23 cm2 active area under 100 mW/cm2 illumination.

In this paper, we have studied the effect of the thickness of a CH3NH3PbI3 perovskite overlayer on mesoporous TiO2 electrodes in perovskite solar cells. The overlayers were prepared by spin coating PbI2 films on the electrodes, which were subsequently exposed to a CH3NH3I/2-propanol solution. We controlled the thickness of the perovskite overlayer by changing the PbI2 solution concentration. The thicknesses of the overlayers spin-coated from 0.5, 0.75, 0.9, and 1 M PbI2 solutions were approximately 179, 262, 316, and 341 nm, respectively. Perovskite solar cells with an approximately 316-nm-thick overlayer showed the highest efficiency of 9.11%. We conclude that optimization of the perovskite overlayer thickness in the solar cell structure is necessary to improve the cell efficiency.

The purpose of the present study is to investigate the optical and the structural properties of CuIn1−xGaxSe2 (CIGS) thin films with various Ga/[In+Ga] ratios grown by using the coevaporation technique. The Ga ratios were 0, 0.15, 0.29, 0.40, 0.56, 0.73, and 1. As the Ga/[In+Ga] ratio increased, the grain size of CIGS films decreased, and the X-ray diffraction (XRD) peaks of the CIGS films progressively shifted to higher diffraction angles. In the cross-sectional scanning electron microscopy (SEM) images, the grain size of the CIGS thin films near the molybdenum electrode was smaller than it was near the CIGS surface. These results indicate that the diffusion rates of elements were different. The photocurrent (PC) spectra also showed that the band gap energy of the CIGS films increased as the Ga/[In+Ga] ratio increased. Accordingly, the short-circuit current density (JSC) linearly decreased, and the open-circuit voltage (VOC) increased and saturated at high Ga/[In+Ga] ratios (x > 0.4) due to the defects on the CIGS films surface. A correlation between the Ga/[In+Ga] ratio and the number of surface defects for the CIGS films is discussed.