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A cylindrical Si 3 N 4 nanopattern whose heights was 200 nm was fabricated on a glass substrate, and an aluminum-doped zinc oxide (AZO) layer was grown on the nanopatterned glass substrate. The nanopattern was applied to an amorphous silicon solar cell in order to increase the light-scattering effect, thus enhancing the efficiency of the solar cell. The reflectance of the solar cell on the Si 3 N 4 nanopattern decreased and its absorption increased. Compared to a flat substrate, the short-circuit current density ( J sc ) and conversion efficiency of a solar cell on the Si 3 N 4 nanopatterned substrate were improved by 17.9% and 24.2%, respectively, as determined from solar simulator measurements.

One of the fabrication issues in hetero-junction crystalline Si solar cells is the overhead time between the deposition steps of the top and bottom surfaces, because flipping of the progressing wafer is necessary to process the both sides of the wafer. To reduce the overall processing time by reducing the overhead time, we propose a dual-chamber deposition system, where thin films on the top and bottom surfaces of the Si wafer are simultaneously deposited. We have evaluated the proposed deposition system by demonstrating fabricated hetero-junction crystalline Si solar cells, which were compared with solar cells fabricated by a conventional plasma-enhanced chemical deposition system. We have obtained the power conversion efficiency of 15.5% from solar cells fabricated by our dual-chamber system; and additional analyses confirmed that the proposed dual-chamber system is, in principle, competitive with conventional systems in terms of the fabricated solar cell performance. This novel concept for the fabrication of a hetero-junction crystalline Si solar cell is expected to lay an important foundation in the future thin film crystalline Si based photovoltaic industry.

We present three dimensional ( 3-D ) amorphous silicon (a-Si:H) thin-film solar cells with silver nano -rods as back electrodes, which are fabricated by low cost nano imprint lithography (NIL). After conformal deposition of thin metal and semiconductor layers, we can achieve a dome-shaped geometry, which is shown to be effective in reducing the reflectance at the front surface due to the graded refractive index effect. In addition, the enhancement of the diffused reflectance over a broad wavelength in this dome-shaped geometry provides light trapping due to the increase in the effective light propagation length. Using this 3-D solar cell, we achieved 54% increase in short circuit current density and 45% increase in the conversion efficiency compared to the control cells with flat Ag surfaces. This 3-D structure can be also used for improving light harvesting in various photovoltaic devices regardless of materials and structures.

A reduction in silicon material consumption in the photovoltaic industry is required for cost reduction. Using crystalline silicon wafers of less than 120 microns of thickness is a promising way for cost and material reduction in the solar cell production. The standard thickness of crystalline silicon solar cells is currently around 180 microns. If the wafers are thinner than 100 microns in the silicon solar cells, the amount of silicon will be reduced by almost half, which should result in prominent cost reduction. With this aim, many groups have worked with thin crystalline silicon wafers. However, most of them have studied with small size substrates. In this paper, we present the electrical characteristics for thin single crystalline silicon solar cells of 100 and 115 μm thickness and 156×156 mm2 area manufactured through a conventional process. We have achieved 17.2% conversion efficiency with a 115 μm silicon substrate and 16.8% with a 100 μm substrate. This enables the commercialization of the thin crystalline silicon solar cells with high conversion efficiency. We also suggest issues to be solved in thin crystalline silicon solar cell manufacturing.

We have incorporated silicon nanoparticles (Si-nps) into organic–inorganic hybrid solar cells in place of the chalcogenide nanocrystals that are commonly employed in such devices. Poly(3,4-ethylenedioxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS) and phenyl-C61-butyric acid methyl ester (PCBM) were employed as hole and electron transport layers, respectively. We used transmission electron microscopy, Raman spectroscopy, and ultraviolet–visible spectroscopy to fully characterize the Si-nps and relate their characteristics to the performance of the hybrid solar cells. We show that the open circuit voltage (VOC) was largely dependent on the size and amorphous volume fraction of Si-nps. Our findings imply that the amorphous phase and small size of Si-nps produce band gap widening that increases the VOC when coupled with PCBM as acceptor. The maximum VOC was up to 0.634 V in a hybrid device with 5.7 nm Si-nps.

We demonstrate a practical route to synthesize Ge nanoparticles (NPs) in multi-gram quantities via the laser pyrolysis of GeH4 gas. The size of the as-produced Ge NPs can be precisely controlled in the range of 19.0 to 65.9 nm via a subsequent etching procedure using a dilute H2O2 solution. Stable water dispersions of Ge NPs yield particles with a Ge/GeO2 core-shell structure, however, the oxide shell can easily be removed and passivated by treatment with HCl. The feed materials used in this process are readily available and lead to non-toxic, water-based dispersions of Ge NPs. The scalability and convenience of this procedure make it attractive as a method to obtain Ge NP dispersions for use in applications such as optoelectronic devices and biosensors.

Catholic University of Daegu, 13 13 Hayang-ro, Hayang-eup, Gyeongsan-si, Gyeongbuk 712-702, KoreaInductively coupled nonthermal plasma has been utilized to synthesize size-tunable germaniumnanoparticles (Ge NPs). Process pressure and radio-frequency (RF) power were modulated toinvestigate their effects on the size distribution of the synthesized Ge NPs. The size of the NPs wasdetermined using transmission electron microscope (TEM) images. X-ray diffraction (XRD) analysesand Raman spectroscopy measurements were utilized to con“rm the crystallinity of the synthesizedGe NPs. The consistency between the XRD analysis and the diffraction patterns from the TEManalysis indicated that the synthesized the Ge NPs were crystalline. Ge NPs with a mean diameterof less than 10 nm can be synthesized under proper experimental conditions.

Two types of carboxylic acid functionalized fullerence derivatives, 4-(2-ethylhexyloxy)-[6,6]-phenyl C61-butyric acid (p-EHO-PCBA) and bis-4-(2-ethylhexyloxy)-[6,6]-phenyl C61-butyric acid (bis-p-EHO-PCBA), were synthesized and investigated as an interfacial layer for inverted polymer solar cells (iPSCs). The –COOH groups on the PCBAs chemisorb to inorganic metal oxide (TiOX), generating fullerene-based self-assembled monolayers (FSAMs). The devices with the mono- and bis-FSAMs exhibited substantially lower series resistance (RS) values of 2.10 Ω cm2 and 1.46 Ω cm2, compared to that (4.15 Ω cm2) of the unmodified device. The TiOX films modified with mono- and bis-FSAMs showed higher contact angles of 50° and 91°, respectively, than that of the pristine TiOX film (33°). The increased contact angles were attributed to the enhanced hydrophobicity, improving the wetting properties with the organic photoactive layer. In addition, a comparison of device characteristics with electroactive FSAMs and non-electroactive benzoic acid SAMs clearly indicates that the FSAMs may suggest an additional pathway for photo-induced charge transfer and charge collection to ITO. After surface modification with FSAMs, the short-circuit current density (JSC) and fill factor (FF) values increased substantially. The iPSCs based on poly(5,6-bis(octyloxy)-4-(thiophen-2-l)benzo[c][1,2,5]thiadiazole) (PTBT) and [6,6]phenyl-C61-butyric acid methyl ester (PCBM) as an active layer showed remarkably improved power conversion efficiency up to 5.13% through incorporation of the FSAMs-based interfacial layer.

Cycloaddition is one of the best-studied types of reactions in the organic chemistry of fullerenes, engendering [6,6]-closed adducts in the vast majority of cases. Notwithstanding that a formation of open fulleroid structures is undoubtedly of theoretical interest, no one has demonstrated the conformation of [5,6]-open fulleroid via the direct cycloadditions. Here, we establish that cycloaddition between C 60 and benzyne in situ generated from 2-amino-4,5-dibutoxybenzoic acid affords a new type of elusive [5,6]-open structure that is characterized on the basis of NMR, UV–vis spectroscopy, and cyclic voltammetry. Additionally, from density functional theory (DFT) calculations for possible [5,6]-open and [6,6]-closed adducts induced of benzyne-C 60 reaction, as expected, features such as the charge distributions, binding characteristics, and frontier molecular orbital levels, are affected by the different binding modes in C 60 cage.

The doping process in diffusion furnace consisting of pre-deposition and drive-in steps is essential to create p–n junction in crystalline silicon solar cell fabrication, and its optimization is necessary to obtain the high conversion efficiency. In this work, pre-deposition time was varied to study the electrical properties of solar cells and its effect on the hydrogen passivation with various phosphorous doping profiles. As a result, solar cell conversion efficiency of 17.8% with 7 min pre-deposition was achieved. Dopant (phosphorous) concentration in the emitter measured by SIMS indicated that the surface with shorter pre-deposition time had lower dopant concentration. High concentration of phosphorous on the surface appears to be the source for the electron consumed by the stored hydrogen in making the neutral H 2 gas during firing. The formation of neutral hydrogen gas is thermodynamically and stochastically more favorable than the reaction between Si with dangling bond and H. This means that the passivation by the stored H during firing is strongly controlled by the dopant on the surface. This result obtained herein lays the foundations to understand the relationship between the doping profile of diverse dopant species and its passivation effect.

© 2016, National Academy of Sciences. All rights reserved. Emerging classes ofconcentrator photovoltaic (CPV) modules reach efficiencies that are far greater than those of even the highest performance flat-plate PV technologies, with architectures that have the potential to provide the lowest cost of energy in locations with high direct normal irradiance (DNI). A disadvantage is their inability to effectively use diffuse sunlight, thereby constraining widespread geographic deployment and limiting performance even under the most favorable DNI conditions. This study introduces a module design that integrates capabilities in flat-plate PV directly with the most sophisticated CPV technologies, for capture of both direct and diffuse sunlight, thereby achieving efficiency in PV conversion of the global solar radiation. Specific examples of this scheme exploit commodity silicon (Si) cells integrated with two different CPV module designs, where they capture light that is not efficiently directed by the concentrator optics onto large-scale arrays of miniature multijunction (MJ) solar cells that use advanced III-V semiconductor technologies. In this CPV+scheme ("+" denotes the addition of diffuse collector), the Si and MJ cells operate independently on indirect and direct solar radiation, respectively. On-sun experimental studies of CPV+modules at latitudes of 35.9886° N (Durham, NC), 40.1125° N (Bondville, IL), and 38.9072° N (Washington, DC) show improvements in absolute module efficiencies of between 1.02% and 8.45% over values obtained using otherwise similar CPV modules, depending on weather conditions. These concepts have the potential to expand the geographic reach and improve the cost-effectiveness of the highest efficiency forms of PV power generation.

Quantitative estimation of the specific contact resistivity and energy barrier at the interface between transparent conducting oxide (TCO) and hydrogenated p-type amorphous silicon carbide (a-Si1 − xCx:H(p)) was carried out by inserting an interfacial buffer layer of hydrogenated p-type microcrystalline silicon (μc-Si:H(p)) or hydrogenated p-type amorphous silicon (a-Si:H(p)). In addition, superstrate configuration p–i–n hydrogenated amorphous silicon (a-Si:H) solar cells were fabricated by plasma enhanced chemical vapor deposition to investigate the effect of the inserted buffer layer on the solar cell device. Ultraviolet photoelectron spectroscopy was employed to measure the work functions of the TCO and a-Si1 − xCx:H(p) layers and to allow direct calculations of the energy barriers at the interfaces. Especially interface structures were compared with/without a buffer which is either highly doped μc-Si:H(p) layer or low doped a-Si:H(p) layer, to improve the contact properties of aluminum-doped zinc oxide and a-Si1 − xCx:H(p). Out of the two buffers, the superior contact properties of μc-Si:H(p) buffer could be expected due to its higher conductivity and slightly lower specific contact resistivity. However, the overall solar cell conversion efficiencies were almost the same for both of the buffered structures and the resultant similar efficiencies were attributed to the difference between the fill factors of the solar cells. The effects of the energy barrier heights of the two buffered structures and their influence on solar cell device performances were intensively investigated and discussed with comparisons.

Hydrogenated amorphous-silicon (a-Si:H) thin-film solar cells have advantages of relatively simple technology, less material consumption, higher absorption ratio compared to crystalline silicon, and low cost due to the use of cheaper substrates rather than silicon wafers. However, together with those advantages, amorphous-silicon thin-film solar cells face several issues such as a relatively lower efficiency, a relatively wider bandgap, and the Staebler-Wronski effect (SWE) compared to other competing materials (i.e., crystalline silicon, CdTe, Cu(InxGa(1−x))Se2 (CIGS), etc.). As a remedy for those drawbacks and a way to enhance the cell conversion efficiency at the same time, the employment of crystalline silicon nanoparticles (Si-NPs) in the a-Si matrix is proposed to organize the quantum-dot (QD) structure as the light-absorbing layer. This structure of the light absorbing layer consists of single-crystal Si-NPs in an a-Si:H thin-film matrix. The single-crystal Si-NPs are synthesized by using SiH4 gas decomposition with CO2 laser pyrolysis, and the sizes of Si-NPs are calibrated to control their bandgaps. The synthesized size-controlled Si-NPs are directly transferred to another chamber to form a QD structure by using co-deposition of the Si-NPs and the a-Si:H matrix. Transmission electron microscopy (TEM) analyses are employed to verify the sizes and the crystalline properties of the Si-NPs alone and of the Si-NPs in the a-Si:H matrix. The TEM results show successful co-deposition of size-controlled Si-NPs in the a-Si:H matrix, which is meaningful because it suggests the possibility of further enhancement of the a-Si:H solar-cell structure and of tandem structure applications by using a single element.

We report the effect of antireflective disordered submicron structures (d-SMSs) on glass substrates for the absorption enhancement of thin-film solar cells. The shape and height of d-SMSs were designed on the basis of the calculation result from the rigorous coupled wave analysis (RCWA) method. The d-SMSs with tapered shape were fabricated on the back side of SnO2:F covered glass substrate by plasma etching of thermally dewetted silver (Ag) nanoparticles without any lithography processes. The glass substrates with d-SMSs showed very low reflectance compared to that of the glass substrates with flat surface over a wide specular and angular range. Thin-film hydrogenated amorphous silicon (a-Si:H) solar cells were prepared on the opposite side of d-SMSs integrated glass substrates, and the devices exhibited a short-circuit current density (Jsc) of 6.84% increased value compared to the reference cells with flat surface without detrimental changes in the open circuit voltages (Voc) and fill factor. Also, it is found that the performance of the solar cells is sustained over a wide incident angle of light.

When amorphous silicon thin film is deposited on n-type c-Si substrate, partial epi-layer of silicon grows mainly on the valley of the pyramid where two (1 1 1) planes meet. The epi-layer degrades a-Si/c-Si interface properties. This is the main cause which leads to a decrease in the efficiency of silicon heterojunction solar cells. In this study, we made various texture shapes of silicon substrate for heterojunction solar cells with n-type silicon wafers. Four different types of textures on silicon heterojunction were prepared: large textured, smoothened large textured, small textured, and smoothened small textured. Surface texturing is well known as one of the major paths to improving the efficiency of silicon solar cells by increasing the short-circuit current through effective photon trapping. The results were successful for silicon random texturing using potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) solutions. Silicon heterojunction solar cells were fabricated on textured substrates, indicating the feasibility of KOH and TMAH texturing for solar cell fabrication. We obtained images of the surface morphology using a scanning electron microscope. The interface cross-section was taken using a transmission electron microscope. We gained the optimized surface morphology of silicon substrate for a-Si/c-Si interface in silicon heterojunction solar cells.

Al-doped zinc oxide/silver (ZnO:Al/Ag) back reflectors for silicon thin-film solar cells with an n–i–p configuration were prepared on flexible stainless steel substrates by dc magnetron sputtering. The surface morphologies of the back reflectors were modified by changing the deposition temperature of the Ag films to improve the light-scattering properties on the back reflectors, resulting in the enhancement of the light-trapping effect in the solar cells. By elevating the deposition temperature from room temperature to 500 °C, the surface roughness of the Ag films increased from 6.62 to 46.64 nm. The films at 500 °C had coarse surface features with irregular grain size distributions between 200 and 900 nm, whereas the films produced at low temperatures below 100 °C had smooth surfaces consisting of small grains between 100 and 200 nm. Even after the 100-nm thick ZnO:Al films were deposited on the modified Ag surfaces, the surface microstructure of the ZnO:Al/Ag bilayers was similar to that of the Ag films. The surface roughness of bilayers increased from 7.12 to 39.30 nm with coarsening the Ag surfaces. Haze factor (a ratio of diffuse reflectance to total reflectance) of Ag films was enhanced remarkably from 59% to 74% in a wide wavelength range from 350 to 1100 nm with increasing the surface roughness of the Ag films from 6.62 nm to 46.64 nm. Enhancement in the haze factor was due to the increase of diffuse reflectance on the Ag films, because the total reflectance did not change much with increasing surface roughness of the Ag films. This increasing roughness indicated that the light scattering from the rough surface of the back reflectors improved. The enhanced light scattering from the back reflectors influenced the performance of the solar cells mainly in terms of the short-circuit current density ( J sc ). Compared to the back reflectors with smooth surface features, leading to a J sc value of 9.94 mA/cm 2 , the back reflectors with large surface roughness improved the J sc value of the solar cells to 13.36 mA/cm 2 without detrimental changes in the fill factor (FF) and open circuit voltage ( V oc ); they eventually increased the conversion efficiency of the solar cells from 5.59% to 7.60%.

In this study, we investigated the effect of the multi-step texturing process on the electrical and optical properties of hydrogenated Al-doped zinc oxide (HAZO) thin films deposited by RF magnetron sputtering. After their deposition, the surface of the HAZO films was multi-step textured in dilute HCl (0.5%) to investigate the change in their optical properties and surface morphology due to etching. The HAZO film fabricated under the type III condition showed excellent optical properties with a haze value of 50.81%. The microcrystalline silicon (μc-Si:H)-based p–i–n solar cells prepared using these new texture-etched HAZO substrates showed high quantum efficiencies in the long wavelength range, thereby demonstrating effective light trapping. Using the optimum AZO:H thin film textured surface, we achieved a p–i–n μc-Si solar cell efficiency of 7.08%.

Textured ZnO:Al films with excellent light scattering properties as a front electrode of silicon thin film solar cells were prepared on glass substrates by an in-line rf magnetron sputtering, followed by a wet-etching process to modify the surface morphologies of the films. Deposition parameters and wet etching conditions of the films were controlled precisely to obtain the optimized surface features. All as-deposited films show a strong preferred orientation in the [001] direction under our experimental conditions. The microstructure of the films was significantly affected by working pressure and film compactness was reduced with increasing working pressure, while the effect of a substrate temperature on the microstructure is less pronounced. A low resistivity of 4.25 x 10- 4 Ω cm and high optical transmittance of above 80% in a visible range were obtained in the films deposited at 1.5 mTorr and 100 °C. After wet etching process, the surface morphologies of the films were changed dramatically depending on the microstructure and film compactness of the initial films. By controlling the surface feature, the haze factor and angular resolved distribution of the textured ZnO:Al films were improved remarkably when compared with commercial SnO 2 :F films. The textured ZnO:Al and SnO 2 :F films were applied as substrates for a silicon thin film solar cells with tandem structure of a-Si:H/μc-Si:H. Compared with the solar cells with the SnO 2 :F films, a significant enhancement in the short-circuit current density of the μc-Si:H bottom cell was achieved, which is due to the improved light scattering on the highly textured ZnO:Al film surfaces in the long wavelength above 600 nm.

Silicon nanoparticles were synthesized using inductively coupled plasma (ICP), and their microstructures were investigated by using scanning electron microscopy, X-ray diraction, and transmission electron microscopy. Applying ICP in a tube reactor, the shape of the plasma region was very sensitive to the process conditions and reactor geometry. For the control of the plasma shapes, an additional inner tube was inserted into the quartz tube reactor. To evaluate the advantages of this double tube reactor, we investigated the microstructures of the silicon nanoparticles synthesized in this manner under various process conditions. This additional tube reduced the length of the plasma zone and formed highly-dense plasma only near the ICP coil. Injection of the reactive gas through the inner tube resulted in the formation of single-crystalline nannoparticles with 13.47 nm diameters.

This study addresses the optimization of rf magnetron-sputtered hydrogenated ZnO:Al (HAZO) films as front contacts in microcrystalline silicon solar cells. The front contact of a solar cell has to be highly conductive and highly transparent to visible and infrared radiation. Furthermore, it has to scatter the incident light efficiently in order for the light to be effectively trapped in the underlying silicon layers. In this research, HAZO films were rf-magnetron-sputtered on glass substrates from a ceramic (98 wt% ZnO, 2 wt% Al 2 O 3 ) target. Various compositions of AZO films on glass substrates were prepared by changing the H 2 /(Ar + H 2 ) ratio of the sputtering gas. The resulting smooth films exhibited high transparencies ( T ⩾ 85% for visible light including all reflection losses) and excellent electrical properties ( ρ = 2.7 × 10 −4 Ω · cm). Depending on their structural properties, these films developed different surface textures upon post-deposition etching using diluted hydrochloric acid. The light-scattering properties of these films could be controlled simply by varying the etching time. Moreover, the electrical properties of the films were not affected by the etching process. Therefore, within certain limits, it is possible to optimize the electro-optical and light-scattering properties separately. The microcrystalline silicon (μc-Si:H)-based p–i–n solar cells prepared using these new texture-etched AZO:H substrates showed high quantum efficiencies in the long wavelength range, thereby demonstrating effective light trapping. Using the optimum AZO:H thin-film textured surface, we achieved a p–i–n μc-Si solar cell efficiency of 7.78%.

We fabricated point-contacted a-Si:H(p)/c-Si(n) heterojunction solar cells using patterned SiO 2 and investigated their electrical properties using the light current–voltage ( I–V ) curve and Suns- V oc measurements. The light I–V curves showed bias-dependent changes according to the applied voltage in the point-contacted cells, especially in the samples with a long distance between the point-contacted junctions. The Suns- V oc measurements showed that the bias-dependence of the light I–V curves did not originate from the recombination in the SiO 2 /Si or a-Si:H(p)/c-Si(n) interface, but from the series resistances. It is possible to explain the bias-dependent light I–V curve in terms of the conductivity of a-Si:H(p) and difference in the electrical contact properties between a-Si:H(p), ZnO and c-Si(n). These results mean that the electrical properties of the a-Si:H(p) layer and the contact properties with this layer are also critical to obtain a high J sc and fill factor in n-type based Si heterojunction solar cells.

This study is devoted to the formation of high–low-level-doped selective emitter for crystalline silicon solar cells for photovoltaic application. We report here the formation of porous silicon under chemical reaction condition. The chemical mixture containing hydrofluoric and nitric acid, with de-ionized water, was used to make porous on the half of the silicon surface of size 125×125 cm. Porous and non-porous areas each share half of the whole silicon surface. H 3 PO 4 :methanol gives the best deposited layer with acceptable adherence and uniformity on the non-porous and porous areas of the silicon surface to get high- and low-level-doped regions. The volume concentration of H 3 PO 4 does not exceed 10% of the total volume emulsion. Phosphoric acid was used as an n-type doping source to make emitter for silicon solar cells. The measured emitter sheet resistances at the high- and low-level-doped regions were 30–35 and 97–474 Ω/□ respectively. A simple process for low- and high-level doping has been achieved by forming porous and porous-free silicon surface, in this study, which could be applied for solar cells selective emitter doping.

In silicon heterojunction solar cells, a thin intrinsic amorphous-silicon (a-Si:H) buffer layer between a doped emitter and a c-Si wafer is essential to minimize carrier recombination. This study examines the effect of H 2 dilution on the properties of the intrinsic a-Si:H layers deposited on Si wafers by plasma-enhanced chemical vapor deposition. A H 2 /SiH 4 ratio of 2∼4 led to improvements in the quality of intrinsic a-Si:H films and in the performance of passivation compared to a-Si:H film without H 2 dilution. A high H 2 -dilution ratio, however, degraded the passivation of the a-Si:H film. The Si heterojunction solar cells with an optimal intrinsic a-Si:H layer showed an efficiency of 12.3%.

Effects of heat treatment in nitrogen or Se atmosphere on the properties of Cu(In,Ga)Se 2 (CIGS) nanoparticles were investigated to extract optimum sintering conditions for fabrication of solar cell applicable CIGS absorber films. In nitrogen atmosphere, as the temperature increases from 100 to 400 °C the intensity of X-ray diffraction (XRD) peaks corresponding to the (1 1 2), (2 2 0) and (3 1 2) planes of the chalcopyrite CIGS increases, and the peak positions shift to lower angle regions without any particle growth in scanning electron microscopy (SEM) analysis, which is in consistent with the significant In and Ga loss in the EDS data. When the temperature further goes up to 500 °C, parts of CIGS are decomposed and Cu and CuSe 2 phases are observed. From these results, the heat treatment in nitrogen atmosphere is found to have no beneficial effect on the sintering of the particles and only induces loss of In and Ga. On the other hand, heat treatment in Se atmosphere at a substrate temperature of 550 °C with Se vapor evaporated at 250 and 450 °C provided much enhanced growth of the particles, specially up to 500 nm at 450 °C, and increased crystallinity without In or Ga loss, reflecting that Se supply played a critical role in the growth of the CIGS nanoparticles.

We report on the electrical and optical characteristics of a-Si:H/c-Si heterojunction solar cells with point-contact junction via patterned SiO 2 layer at the interface. The new structure showed improved electrical properties, having a smaller leakage current and a larger shunt resistance. The electrical conduction of the point-contacted samples followed the diffusion dominant process with bulk recombination, but the control samples without SiO 2 showed the space-charge region recombination dominant process. The point-contacted samples showed increased internal quantum efficiency in the bulk region, but decreased internal quantum efficiency in the surface region. As the distance between the holes decreased, the point-contacted solar cells showed an improved efficiency with a larger fill-factor but smaller open-circuit voltage and short-circuit current.

Superstrate p-i-n amorphous silicon thin-film (a-Si:H) solar cells are prepared on SnO2:F and ZnO:Al transparent conducting oxides (TCOs) in order to see the effect of TCO/p-layers on a-Si:H solar cell operation. The solar cells prepared on textured ZnO:Al have higher open circuit voltage Voc than cells prepared on SnO2:F. The presence of a thin microcrystalline p-type silicon layer (μc-Si:H) between ZnO:Al and p a-SiC:H plays a major role by causing an improvement in the fill factor as well as in Voc of a-Si:H solar cells prepared on ZnO:Al TCO. Without any treatment of the p-i interface, we could obtain a high Voc of 994 mV while keeping the fill factor (72.7%) and short circuit current density Jsc at the same level as for the cells on SnO2:F TCO. This high Voc value can be attributed to modification in the current transport in this region due to creation of a potential barrier.

CuIn1-xAxlSe2(CIAS) films were obtained by selenization process of metallic precursors. The metallic precursors were deposited sequentially by using sputtering system. As the ratio of Al/(Al+In) in the precursors increased, the chalcopyrite (112) peak shifted to high value and the band-gap of CIAS layer increased to 1.38 eV. However, the bi-layer morphology with well crystallized large grain on the surface and small grain thin bottom layer was observed. Although the sequences of precursors were changed in order to get uniform layer, no distinguishable difference was not observed.

The photovoltaic properties of CIGS cells on an alumina substrate were improved through the use of Na-doped Mo as the bottom layer of a Mo back contact. Na was supplied to the CIGS bulk region from an alumina/Na-doped Mo/Mo structure, similar to the Na diffusion from soda-lime glass. The diffusion of Na from the Na-doped Mo was controlled effectively compared to that from Soda-lime glass (SLG). The present results indicate that Na-doped Mo acts as a Na source material and that the Na amount can be controlled by adjustment of thickness of Na-doped Mo layer, without the use of an alkali barrier layer. The highest conversion efficiency of 13.34% ( J sc = 34.62 mA/cm 2 , V oc = 0.58 V and FF = 66%) for an active area of 0.45 cm 2 on an alumina substrate was obtained for 100 nm Na-doped Mo/1000 nm Mo.

Semiconducting materials are central to the development of high-performance electronics that are capable of dissolving completely when immersed in aqueous solutions, groundwater, or biofluids, for applications in temporary biomedical implants, environmentally degradable sensors, and other systems. The results reported here include comprehensive studies of the dissolution by hydrolysis of polycrystalline silicon, amorphous silicon, silicon-germanium, and germanium in aqueous solutions of various pH values and temperatures. In vitro cellular toxicity evaluations demonstrate the biocompatibility of the materials and end products of dissolution, thereby supporting their potential for use in biodegradable electronics. A fully dissolvable thin-film solar cell illustrates the ability to integrate these semiconductors into functional systems.

Silicon nanocrystals (Si NCs) with an average diameter of 17.7 nm were synthesized using a flow-through, inductively-coupled nonthermal plasma. The crystalline Si nanoparticles (NPs) were confirmed by using transmission electron microscope (TEM) images, X-ray diffraction (XRD) analyses, and Raman spectroscopy measurements. In addition, scanning electron microscope (SEM) measurements showed that the use of a nonthermal plasma prevented the agglomeration of the Si NPs. These Si NCs synthesized by using a nonthermal plasma can be applied to various interesting fields such as photovoltaic cells, labels for biosensors, light-emitting diodes, and so forth.

The polycrystalline silicon (poly-Si) films are deposited on low-temperature glass substrate by hot-wire CVD. The SiH 4 gas flow rate {F(SiH 4 )} is a critical parameter both for deposition rate and for crystalline properties. The poly-Si films deposited at low F(SiH 4 ) with moderate deposition rate (about 3 μm/h) have superior crystalline properties and crystalline volume fraction that exceeds 90%. The films also have natural texture structure on the surface that is strongly recommended in thin-film solar cells in order to obtain high current density by increasing incident light trapping. By increasing F(SiH 4 ) to 10 sccm, the high deposition rate (20 μm/h) is obtained, but crystalline properties deteriorated in these samples. However, these films have high potentials for thick (20-30 μm) solar cell applications due to the high deposition rate and enhanced grain growth; average grain sizes are larger than that of low-F(SiH 4 ) samples although small nano-sized grains still exist, by which crystalline volume fraction was

The silicon nitride films were deposited by means of high-density inductively coupled plasma chemical vapor deposition in a planar coil reactor. The process gases used were pure nitrogen and a mixture of silane and helium. Passivated by silicon nitride, solar cells show efficiency above 13%. Strong H-atom release from the growing SiN film and Si–N bond healing are responsible for the improved electrical and passivation properties of SiN film. This paper presents the optimal refractive index of SiN for single layer antireflection coating as well as double layer antireflection coating in solar cell applications.

This paper presents the deposition and characterization of polycrystalline silicon (poly-Si) films by the hot-wire chemical vapor deposition (HWCVD) method. The filament temperature was determined to be a critical parameter for the deposition of large-grained Si films. Poly-Si films with a moderate lateral grain-size of ∼1 μm and a vertical grain size approximately the same as the film thickness (approx. 3 μm) could be deposited on a glass substrate at a substrate temperature of less than 550°C by increasing the filament temperature to 2000°C. The surface of the films has a natural textured structure, which is believed to give some positive effects on solar cell performance. Some experimental results are presented in order to elucidate these improvements in crystalline properties of the Si films deposited at high filament temperature.

Transparent ZnO films were prepared by rf magnetron sputtering, and their electrical, optical, and structural properties were investigated under various sputtering conditions. Aluminum-doped n-type(n-ZnO) and undoped intrinsic-ZnO (i-ZnO) layers were deposited on a glass substrate by incorporating different targets in the same reaction chamber. The n-ZnO films were strongly affected by argon ambient pressure and substrate temperature, and films deposited at 2 mTorr and 100°C showed superior properties in resistivity, transmission, and figure of merit (FOM). The sheet resistance of ZnO film was less dependent on film thickness when the substrate was heated during deposition. These positive effects of elevated substrate temperature are presumably attributed to the rearrangement of the sputtered atoms by the heat energy. Also, the films are electrically uniform through the 5 cm×5 cm substrate. The maximum deviation in sheet resistance is less than 10%. All of the films showed strong (0 0 2) diffraction peak near 2θ =34°. The undoped i-ZnO films deposited in the mixture of argon and oxygen gases showed high transmission properties in the visible range, independent of the Ar/O2 ratio, while resistivity rose with increased oxygen partial pressure. The Cu(In,Ga)Se2 solar cells, incorporating bi-layer ZnO films (n-ZnO/i-ZnO) as window layer, were finally fabricated. The fabricated solar cells showed 14.48% solar efficiency under AM 1.5 conditions (100 mW/cm2).

Hybrid solar cells, based on organic and inorganic semiconductors, are a promising way to enhance the efficiency of solar cells because they make better use of the solar spectrum and are straightforward to fabricate. We report on a new hybrid solar cell comprised of hydrogenated amorphous silicon (a-Si:H), [6,6]-phenyl-C71-butyric acid methyl ester ([71]PCBM), and poly-3,4-ethylenedioxythiophene poly styrenesulfonate (PEDOT:PSS). The properties of these PEDOT:PSS/a-Si:H/[71]PCBM devices were studied as a function of the thickness of the a-Si:H layer. It was observed that the open circuit voltage and the short circuit current density of the device depended on the thickness of the a-Si:H layer. Under simulated one sun AM 1.5 global illumination (100 mW cm(-2)), a power conversion efficiency of 2.84% was achieved in a device comprised of a 274 nm-thick layer of a-Si:H; this is the best performance achieved to date for a hybrid solar cell made of amorphous Si and organic materials.

The p-a-Si1-xCx:H alloy is popularly knows as a wide band gap semiconducting alloy. It was demonstrated in the 1980s that application of the p-a-Si1-xCx:H alloy leads to improved per‐ formance of a solar cell with better blue response of its quantum efficiency (QE) [1]. There are few other well known wide band gap alloy materials available, however one interesting advantage of the p-a-Si1-xCx:H is that both the C and Si are four fold coordinated atoms, and hence a suitably prepared material may attain wider optical gap with good stability.

Studies of the interaction between hydrogen and graphene have been increasingly required due to the indispensable modulation of the electronic structure of graphene for device applications and the possibility of using graphene as a hydrogen storage material. Here, we report on the behaviour of molecular hydrogen on graphene using the gate voltage-dependent resistance of single-, bi-, and multi-layer graphene sheets as a function of H-2 gas pressure up to 24 bar from 300 K to 345 K. Upon H-2 exposure, the charge neutrality point shifts toward the negative gate voltage region, indicating n-type doping, and distinct Raman signature changes, increases in the interlayer distance of multi-layer graphene, and a decrease in the d-spacing occur, as determined by TEM. These results demonstrate the occurrence of dissociative H-2 adsorption due to the existence of vacancy defects on graphene.

We propose a thin film solar cell structure that enables ultrathin film absorber application and single material multi-junction structure. This proposal is targeting amorphous Si only multi-junction solar cells on a patterned transparent electrode, which might perform high light harvesting efficiency and high output voltage at the same time. In addition, photon management of this proposed structure does not rely on traditional light trapping scheme but rather on lateral collection scheme with ‘sidewall solar cells’. To implement the proposed solar cells, a suitable process sequence is suggested, where a challenging node separation process between sidewall solar cells is included. In this work, we present a-Si solar cell on patterned TCO without node separation. We found the signature of absorption path elongation by sidewall solar cells, which is one of the essential principles of our proposed solar cell. This proposal would provide a promising route to a high performance and low cost a-Si only photovoltaics.

Silicon nanoparticles were synthesized by passing monosilane through a quartz tube wrapped with Inductive Coupled Plasma (ICP) coil. Microstructures of synthesized silicon nanoparticles were investigated with various process conditions. To research the effects of process parameters on the properties of nanoparticles, we verified the partial pressure of monosilane, the plasma power and the working pressure. The highly crystalline silicon nanoparticles were only achieved at the proper partial pressure of the reactive gas and plasma power. Partial pressure determined not only the particle size but also the crystallinity of the nanoparticles. The plasma power was controlled from 50 to 100 W which determined not the particle size but the crystallinity of nanoparticles. Especially, too low a power resulted in amorphous particles with an average sizes of 5.25 nm. As the working pressure increased, the amount of produced nanoparticles linearly increased and the maximum production yield was at 76 mg/hr. Controlling those parameters, we achieved monodispersed single crystalline silicon nanoparticles with an average diameter of 7.52 nm. Silicon nanoparticles in this study can be applied to light absorbing material for solar cells and the wavelength down-converter material of Light Emitting Diode (LED).

Silicon (Si) has received great interest due to its wide variety of advantages such as material abundance, non-toxicity, and strong infra of technologies in semiconductor industries. On the other hand, the cost of silicon wafer has driven many researchers to develop the silicon-based thin film solar cells to reduce the silicon consumption in the industry process. In this sense, the silicon-based thin film solar cells including hydrogenated amorphous and microcrystalline silicon (a-Si:H, μc-Si:H) have good advantage in cost saving. However, a-Si:H solar cells have weaknesses in low efficiency (∼9 %), light induced degradation, too high bandgap separation (1.7–1.8 eV) compared to its competing materials (i.e., crystalline silicon, CdTe, and CIGS) for photovoltaic applications. To cope with these relative weaknesses of current silicon-based thin film technology, we propose a hybrid-type light absorbing materials with single crystal silicon nano-particles (Si-NPs) prepared by laser pyrolysis within a-Si:H thin film matrix. For this hybrid-type solar cell application, single crystal Si-NPs were synthesized by SiH 4 gas decomposition using CO 2 laser pyrolysis. Many process parameters of laser pyrolysis were calibrated to form Si-NPs with various characteristics. The crystalline properties and sizes of Si-NPs were varied by changing CO 2 laser power, reactive gas pressure, and H 2 /SiH 4 gas flows. Transmission Electron Microscopy (TEM) analyses were employed to verify their sizes and crystallinities according to the process parameters. We found that the laser pyrolysis are controllable to synthesize single crystal Si-NPs with diameters of 5–15 nm and the synthesized Si-NPs are applicable to solar cell fabrication.

In this study, intrinsic a-SiO:H films were prepared by a conventional radio frequency (13.56 MHz) plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of SiH 4 , H 2 and CO 2 . Changes in the optical, electrical and structural properties of the a-SiO:H films were investigated systematically by controlling the deposition parameters, mainly the gas ratio of CO 2 to SiH 4 , and hydrogen dilution concentration. By introducing the CO 2 gas, three kinds of O-related IR features are found at 780, 980 and 2090 cm−1. With increasing the CO 2 /SiH 4 ratio, the absorption at 780 cm−1 strongly coupled to the Si-H and Si-O-Si motions increases noticeably, indicating that the defect density in the films increases because the mode at 780 cm−1 is unique signature of a particularly local geometry related to defects. In order to diminish the defect density level in the films, hydrogen dilution was performed. As the H dilution concentration increases, the defect density is reduced significantly and the photo-conductivity is improved to 10−4 S/cm. Influences of oxygen incorporation into the Si network and H dilution on the performance of a-SiO:H solar cells are also examined in detail.

Sputtered zinc oxide/silver double layers as a back-reflector for silicon thin film solar cells with nip configuration were prepared on the flexible metal substrates. Surface morphologies of Ag films were controlled by changing the deposition conditions such as substrate temperature and film thickness to improve the total/diffused reflectance and light scattering properties of ZnO/Ag back reflectors. The surface roughness of Ag films deposited on the stainless steel substrates increases from 14.1 nm to 36.1 nm with increasing the substrate temperature from room temperature to 500°C. Although the total reflectance of ZnO/Ag back reflectors shows minor variation, the diffused reflectance is enhanced with increasing the surface roughness of Ag films, meaning the light scattering on the rough surfaces is improved significantly. It is also found that the surface roughness of Ag films increases with the film thickness at fixed substrate temperature, resulting in the enhancement of diffused reflectance of ZnO/Ag back-reflectors. Silicon thin film solar cells are fabricated on the back-reflectors with the different surface roughness of Ag layers by PECVD and their cell performances are investigated systematically.

To establish reliable model for long term reliability of a-Si:H PV module, outdoor field aging results and indoor light soaking test has been investigated. For the appropriate comparisons, one type of outdoor system modules and test cells has been fabricated from the same commercial module production line. Severe early stage degradation in outdoor site has been resulted and compared to the indoor aging results. Detailed experiment of indoor aging tests depends on both load condition and cell temperature has been investigated.

This study addresses the role of p-type buffer layers between ZnO:Al (AZO) TCO and p a-SiC:H window layer. When AZO is used as a front TCO in conventional a-Si:H solar cells incorporating p a-SiC:H window, the fill factor (FF) significantly decreases in different with SnO 2 :F (FTO). Various buffer layers with different conductivity and crystalline properties are inserted between AZO and p a-SiC:H and solar cell performances are compared. The FF deterioration of AZO/p a-SiC:H cells is directly related to the interface potential barrier. This potential barrier can be controlled by tuning electron affinity and mobility gap as well as electrical conductivity of buffer layers. The p μc-Si:H buffer improves FF up to 0.72, which results from high conductivity of buffer layer. The p a-Si:H buffers also improves FF although they have similarly low conductivity with p a-SiC:H because of low electron affinity and/or mobility gap.

Al-doped ZnO thin films as a front electrode of silicon pin solar cells were prepared on the glass substrates by rf magnetron sputtering in which working pressure and substrate temperature were controlled precisely. After film deposition, the films were etched by dilute acid solution to obtain the textured surfaces. Material properties of the deposited films were investigated by various analytical methods and especially the light scattering for the textured films was determined by optical scattering parameters-haze and angular distribution function (ADF). The as-deposited ZnO:Al thin films show good electrical resistivity and optical transmittance of about 4.5 × 10−4 Ω·cm and above 80% in the visible wavelength range, respectively. After etching process, surface texture and light scattering are affected significantly by the deposition parameters and etching time. The optimized optical properties and light scattering of the films are obtained at working pressure of 0.5mtorr, substrate temperature of 135°C and etching time of 45 sec.

Effects of crystallinity of the p window layers in the pin solar cells having hydrogenated microcrystalline silicon (μc-Si:H) films as an absorber layer on solar cell performance are investigated through the evaluation of the photovoltaic characteristics of solar cells prepared by varying the gas ratio of SiH 4 /H 2 during the p layer deposition. By Raman scattering spectroscopy analysis, it is observed that the volume fraction of crystalline/amorphous phases (X c ) of p layers decreases from 31.0% to 5.1% with increasing the SiH 4 concentration from 0.2 to 1.0 sccm at fixed H 2 of 180 sccm. Depending on the X c of the p layers, the solar cell performance is affected significantly, where the solar cells with the p window layers of low X c represent good photovoltaic characteristics, namely high open circuit voltage (V oc ) and short circuit current density (J sc ). Some experimental results and discussion about relationship between crystalline structure of p layers and performance of μc-Si:H solar cells will be presented briefly in this paper.