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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.

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%.

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%.

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.

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.

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 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.

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.

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.

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.

The n-type hydrogenated microcrystalline silicon-incorporated silicon oxide (n-μc-SiO:H) films are prepared by 13.56MHz plasma enhanced chemical vapor deposition (rf-PECVD) using SiH 4 , H 2 and CO 2 gases for an inter-layer between the amorphous silicon (a-Si:H) top-cell and the microcrystalline silicon (μc-Si:H) bottom-cell in the thin-film silicon tandem solar cells. The optical and electrical properties of n-μc-SiO:H prepared by varying deposition conditions are investigated. The refractive indices of the films are 2.1∼2.7 at the wavelength of 600nm and the electrical conductivity is ∼ 5×10−3 S/cm. Compared to ZnO:Al inter-layer, the n-μc-SiO:H provides reduced current loss of μc-Si:H bottom-cells as well as enhanced current gain of a-Si:H top-cell which might be due to the reduced absorption of incident light in the n-μc-SiO:H inter-layer. An analysis on tunnel recombination junction using current-voltage measurements shows the non-ohmic behavior when crystalline volume fraction and conductivity of inter-layer are low, resulting in the reduction of the FF and V oc in solar cells. The initial conversion efficiency of 10.66% is achieved in thin film silicon tandem solar cells with n-μc-SiO:H inter-layer.

The passivation characteristic of c-Si wafer with thin a-Si:H layer plays key parameter in a-Si:H/c-Si hetero-junction (HJ) solar cells. The significance of passivation depends not only on the quality of a-Si layers but also condition of c-Si substrate surface. C-Si substrates are textured to pyramid shape for effective absorption of light using NaOH or KOH with IPA. Textured c-Si substrates are different morphology and height of pyramid according to etching time. In this study, a-Si layers were deposited on c-Si substrates having different height of pyramid by PE-CVD method. High silicon pyramid with long etching time resulted into lower reflectance to illuminated light. This surface reflectance characteristic was closely related with short-circuit current (JSC) of heterojunction solar cell while minority carrier life time (MCLT) decides open-circuit voltage (Voc) and Fill Factor (F.F). Surface texturing of c-SI surface showed effects on both optical and electrical characteristics of heterojunction solar cell.

Silicon quantum dots (QDs) thin films and superlattice embedded in SiC matrix are prepared by co-sputtering of pure Si and C targets for all silicon tandem solar cell application. The composition of as-deposited Si 1−x C x precursor films can be controlled by changing rf power of Si and C targets, respectively. The composition x from 0 to 0.43 is investigated by changing C power from 0 to 400W under the fixed Si power of 200W. In Raman spectrum, Si crystalline volume fraction decreases with increasing the composition and there is no phase transition from x ∼ 0.38. The Si QDs with 5 – 10 nm size are clearly observed through high resolution transmission electron microscopy. From the in-situ annealing and XRD analysis, Si signal precipitates to single crystalline phase above 900°. Si-rich SiC/stoichiometric SiC superlattice shows vague interfaces owing to re-arrangement and inter-diffusion after annealing. The absorption coefficient a of the sample shifts a high energy level and appears at 1.2∼1.4eV conjectured to exist Si quantum dots after annealing.

Passivation is the one of important factors in the solar cells. The measurement of effectiveness of the passivation layer was based on quasi-steady-state photoconductance. In the case of the sample which was passivated using p-type amorphous silicon(a-Si:H), the minority carrier lifetime was 8.9μs. When the passivation layer was intrinsic a-Si:H, the minority carrier lifetime was 221.3μs. Considering the minority carrier lifetimes of both samples, silicon heterojunction solar cells were fabricated with and without intrinsic a-Si:H layer. the efficiency of the sample passivated with intrinsic amorphous silicon was 13.52%, whereas it was only 11.58% when this layer was not employed.

ZnO is used as a transparent conducting oxide (TCO) for the front electrode in silicon thin film solar cells because of its low resistivity and high optical transmittance. Hydrogenated Al-doped zinc oxide (AZO:H) thin films were grown on glass by rf magnetron sputtering using a ceramic target (98 wt. % ZnO, 2 wt.% Al 2 O 3 ) in H 2 /Ar ambient. We changed the ratio of H 2 /(Ar+H 2 ) and the substrate temperature from RT to 250 °C. As results, a resistivity of 3.21 × 10−4 Ω·cm was obtained at the 2% H 2 with the substrate temperature of 150□. UV-measurement showed that the optical transmission of AZO:H films was above 85% in the visible range with a widened optical band gap. After deposition, AZO:H films were etched in diluted HCl (0.5%) to investigate the variation of optical properties and surface morphology. The etched films had excellent scattering properties (spectral haze: 52%) and low reflectance. We will present results that demonstrate an improved light trapping due to the textured surface by an etching technique.

CuInSe 2 films were prepared by the doctor blade coating of a low cost precursor solution and subsequent selenization. Precursor solution was prepared by dissolving Cu(NO) 3 and InCl in methanol. The solution was coated onto the Mo/glass substrate with appropriate binder materials. And then the layer was selenized in a vacuum evaporator to convert CuCl and amorphous In to CIS. The Cu/In ratios of the resultant films were investigated as a function of that in the solution and selenization conditions.

This paper briefly introduces silicon based thin film solar cells: amorphous (a-Si:H), microcrystalline (/spl mu/c-Si:H) single junction and a-Si:H//spl mu/c-Si:H tandem solar cells. The major difference of a-Si:H and /spl mu/c-Si:H cells comes from electro-optical properties of intrinsic Si-films (active layer) that absorb incident photon and generate electron-hole pairs. The a-Si:H film has energy band-gap (Eg) of 1.7-1.8 eV and solar cells incorporating this wide Eg a-Si:H material as active layer commonly give high voltage and low current, when illuminated, compared to /spl mu/c-Si:H solar cells that employ low Eg (1.1 eV) material. This Eg difference of two materials make possible tandem configuration in order to effectively use incident photon energy. The a-Si:H//spl mu/c-Si:H tandem solar cells, therefore, have a great potential for low cost photovoltaic device by its various advantages such as low material cost by thin-film structure on low cost substrate instead of expensive c-Si wafer and high conversion efficiency by tandem structure. In this paper, the structure, process and operation properties of Si-based thin-film solar cells will be discussed.

CuGaSe/sub 2/ absorber layers were grown by evaporating elemental Cu, Ga and Se on molybdenum coated soda lime glass substrates using three-stage process with substrate temperature monitoring. The grain size of the films decreased with the increase of Ga composition, but the morphology of the films improved. The optical band gap of the absorbers is around 1.68 eV regardless of Ga concentration. Using these films the solar cells with a structure SLG/Mo/CuGaSe/sub 2//CdS/ZnO/AI were fabricated. Current-voltage characteristics and spectral response measurements were performed to evaluate device parameters and to analyze loss factors. In optimal condition, the absorber film is 1.9 /spl mu/m thick and slightly Ga rich bulk composition [Cu]/[Ga] =0.88 and we obtained V/sub OC/ = 0.81 V, J/sub SC/ = 11.9 mA, ff =0.635 and /spl eta/ = 6.1 %.

CuGaSe2 absorber layers were prepared by evaporating elemental Cu, Ga and Se in three stage on Molybdenum coated soda lime glass. The composition of the resultant film was studied by monitoring the substrate temperature, which decreased when a Cu-Se secondary phase was formed. As the Ga supplement increased during the third stage the void that formed in the beginning of the third stage was removed, while a small grain Ga-rich layer was formed on the surface, resulting in a Cu deficient surface. Therefore, the Voc was improved because of the enhanced surface morphology and the Jsc was reduced, due to the Ga rich layer on of the surface. Under optimal conditions, we achieved a cell performance of Voc = 780 mV, Jsc = 12.9 mA/cm2, ff = 62.5 and ν = 7.3 %.

The effects of SiH/sub 4/ flow and H/sub 2/ dilution on the hot wire silicon films have been studied in this paper. The Si films deposited at low SiH/sub 4/ flow (1 to 7 sccm) have distinct Raman TO mode peak near 520 cm/sup -1/ even at no H/sub 2/ dilution. The microcrystalline to amorphous phase transition, however, occurred at increased SiH/sub 4/ flow above than 10 sccm. The added H/sub 2/ gas does not contribute to the crystallinity improvement of the samples deposited at low SiH/sub 4/ flow while the amorphous films are crystallized as the high H/sub 2/ gases are employed. On the contrary, when the deposition time increased, the crystalline properties are greatly improved; crystalline volume fraction reached up to 75% without H/sub 2/ dilution. The electrical properties and hydrogen bonding configuration as functions of SiH/sub 4/ flow and different dilution conditions are also discussed in the paper.

Three types of patterns acting as light-scattering centers were constructed on bulk glass surfaces and applied to solar cell fabrication. In order to fabricate a scattering center in the transparent conducted oxide (TCO) layer, the SiO2-based solution hydrogen silsesquioxane (HSQ; Dow Corning FOx-16) was used for direct nano-patterning. Direct nano-patterning is a simple and fast process that exploits the solvent permeability of poly(dimethylsiloxane) (PDMS). The nano- and micro-structured SiO2 layer fabricated directs diffused light into the active layer of the solar cell, enabling effective use of this layer. This increases the external quantum efficiency and conversion efficiency of the cell. Additionally, a thinner Si junction was fabricated to ensure the effect of each pattern.

We fabricate silver (Ag) nanoparticles (NPs) on the rear surface of thin film hydrogenated amorphous silicon (a-Si: H) solar cells to enhance the light absorption using spin-coating Ag ink, which can produce Ag NPs by a simple, fast, and inexpensive method. Ink concentration and sintering temperature of the spin-coating Ag ink are optimized to maximize the light absorption in the solar cell by tuning the size and distribution as well as the surface coverage of the Ag NPs. The thickness of a SiNx spacer layer, which was embedded between the solar cell and the Ag NPs for electrical isolation, dependent optical properties of the solar cell is also systematically investigated. The thin film a-Si: H solar cell with a thin SiNx spacer layer and the Ag NPs showed great potential for realizing cost-effective high-efficiency solar cells. (C) 2014 Optical Society of America

P-layer of a p-i-n type amorphous silicon solar cell helps in creating a built-in electric field inside the cell; it also contributes to parasitic absorption loss of incident light. Here, we report optimization of these two characteristic contributions of the p-layer of the cell. We used a highly transparent p-type hydrogenated amorphous silicon carbide (p-a-Si 1−x C x :H ) window layer in an amorphous silicon solar cell. With the increased transparency of the p-type layer, the solar cell showed an improvement in short-circuit current density by 17%, along with improvement in blue response of its external quantum efficiency, although further thinner p-layer showed lower open-circuit voltage. Such a cell shows low light-induced degradation and a promise to be used in high-efficiency multijunction solar cell.

The effects of the low-temperature annealing on Zn-doped indium–tin-oxide (ITO) films such as the electrical, optical and structural properties were investigated. Zn-doped ITO films were fabricated by rf magnetron sputtering of ITO and Al-doped ZnO (AZO) targets on corning glass at room temperature. The content of Zn increased with increasing the power of AZO target. The carrier concentration of films shows the decreasing behaviour with increasing the content of Zn, due to a carrier compensation originating from the substitution of a doped Zn for an In or interstitial site. After the low-temperature annealing at 180 °C in vacuum, all films were slightly decreased a carrier concentration and increased the hall mobility because of the absorption of oxygen on the surface films. In addition, the average transmittance did not show a considerable change and had a high values over 80%. Especially, the Zn-doped ITO with atomic ratio of Zn/(In+Zn) of 6.8 at. % had the resistivity of 4×10-4 Ω cm, the highest hall mobility of 41 cm2 V-1 s-1, and the average transmittance of 82%.

The emergence of third-generation photovoltaics based on Si relies on tunable bandgap materials with embedded nanocrystalline Si. One of the most promising approaches is based on the mixed-phase Si1 − x C x . We have investigated the light absorption controllability of nanocrystalline Si-embedded Si1 − x C x produced by thermal annealing of the Si-rich Si1 − x C x and composition-modulated superlattice structure. In addition, stoichiometric SiC was also investigated to comparatively analyze the characteristic differences. As a result, it was found that stoichiometric changes of the matrix material and incorporation of oxygen play key roles in light absorption controllability. Based on the results of this work and literature, a design strategy of nanocrystalline Si-embedded absorber materials for third-generation photovoltaics is discussed.

We demonstrate an organic–inorganic hybrid solar cell using poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and silicon nanocrystals (Si-NCs). To achieve an enhanced response in the hybrid layer, Si-NCs were freshly etched and blended with P3HT/PCBM. The incorporation of Si-NCs into the bulk heterojunction structure induced the coupling of optical excitation between the polymers and Si-NCs and led to an extended optical excitation response. A hybrid solar cell exhibited a 26% increase in JSC relative to an identical cell prepared without the Si-NCs. Consequently, improved power conversion efficiency is obtained by the addition of Si-NCs into polymers.

Aluminum-doped zinc oxide (ZnO:Al) [AZO] is a good candidate to be used as a transparent conducting oxide [TCO]. For solar cells having a hydrogenated amorphous silicon carbide [a-SiC:H] or hydrogenated amorphous silicon [a-Si:H] window layer, the use of the AZO as TCO results in a deterioration of fill factor [FF], so fluorine-doped tin oxide (Sn02:F) [FTO] is usually preferred as a TCO. In this study, interface engineering is carried out at the AZO and p-type a-SiC:H interface to obtain a better solar cell performance without loss in the FF. The abrupt potential barrier at the interface of AZO and p-type a-SiC:H is made gradual by inserting a buffer layer. A few-nanometer-thick nanocrystalline silicon buffer layer between the AZO and a-SiC:H enhances the FF from 67% to 73% and the efficiency from 7.30% to 8.18%. Further improvements in the solar cell performance are expected through optimization of cell structures and doping levels.