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d-Amino acid containing peptides are promising as drug lead compounds because of their expected higher stability in vivo. A heterochiral random peptide library called the one-bead-2n -peptide (OB2n P) library, which can display 2n peptide diastereomers per bead, has been developed. Through screening of the OB2n P library and subsequent binding assay among the peptide diastereomers synthesized in parallel by means of the SPOTs method, new heterochiral mimotopes for the anti-β-endorphin monoclonal antibody have been obtained. One mimotope was a new ligand for the μ-opioid receptor. The screening strategy enabled d-amino acid containing drug leads to be obtained efficiently by expanding searchable chemical space without increasing the experimental scale.

38th European Photovoltaic Solar Energy Conference and Exhibition; 37-40, Installation environments of solar cells are surrounded by heat, which are also exhausted from the cells themselves and degrade the device performance normally. Here we report an experiment to show that hybrid devices of silicon solar cells and commercial thermoelectric materials, bismuth telluride, can recover heat to exhibit a positive temperature characteristic, i.e., the output power increases with the solar cell temperature. The result implies the hybrid structure can be another type of realization for our concept of “heat recovery solar cell”, namely the type II (HERC-II).

d-Amino acid containing peptides are promising as drug lead compounds because of their expected higher stability in vivo. A heterochiral random peptide library called the one-bead-2

36th European Photovoltaic Solar Energy Conference and Exhibition; 478-482, We utilized a chemically grown silicon dioxide (SiO2) layer produced by nitric acid oxidation of silicon (NAOS) formed by various passivation techniques to improve the passivation quality of pyramidal textured surfaces of bifacial passivated emitter and rear cells (PERC) for advanced light management. Two types of symmetrical sample structure, phosphorus-diffused samples and non-diffused samples having the same front and rear sides of a cell, respectively, were fabricated. In this study, we focused on the influence of different oxidation temperatures of NAOS to form the SiO2 layer and thermal annealing in situ hydrogenation conditions on the interfacial properties of the samples. As a result, the non-diffused samples that included the NAOS-SiO2 layer were negatively modified, showing reductions in open-circuit voltage (iVoc) with oxidation temperature and thermal annealing ambient. When the NAOSSiO2 layer was formed at boiling temperature, the iVoc values of non-diffused samples showed further losses compared with samples obtained at room temperature, attributed to the lower density of dangling bonds, exhibiting an increase in interface trap density (Dit). In contrast, the phosphorus-diffused samples passivated by NAOS-SiO2 formed at boiling temperature showed a different behavior, having positive effects on iVoc regardless of the thermal annealing ambient. The disparity of passivation behavior (negative or positive effect) may be related to NAOS-SiO2 thickness as well as different doping surface concentrations. The oxidation temperature for SiO2 formation also plays a key role in obtaining a high level of surface passivation through the hydrogenation process, where the recombination processes in the textured surface of silicon involve many other parameters.

35th European Photovoltaic Solar Energy Conference and Exhibition; 624-627, We propose a fully implanted interdigitated back contact (IBC) silicon solar cell with a gap structure between the emitter and back surface field (BSF) fabricated using a self-aligned process with a single photolithography step. Boron was implanted on the entire rear side. After post-implantation annealing, the oxide layer was grown on the front and rear sides of the silicon wafer. The BSF region was patterned on the rear oxide layer via photolithography. A hollow structure with an overhang of the oxide layer was formed at the boundary between the emitter and BSF during the removal of the oxide and boron-implanted layer on the BSF region via reactive-ion etching and wet chemical etching. The overhanging oxide layer became the mask for subsequent phosphorus implantation on the BSF region.

35th European Photovoltaic Solar Energy Conference and Exhibition; 569-573, This paper demonstrates an improvement of a passivated emitter and rear cell (PERC) with a selective emitter (SE) structure by modifying the ratio between lightly (n+) and highly doped (n++) emitters. To produce the SE structure, screen-printed resist masking combined with wet chemical etch-back was introduced into the conventional PERC process. An adjustment of the ratio of the n+/n++ regions can be achieved by modifying the areas between the unmasked and masked regions through screen-printing on an emitter. The ratio of the n+/n++ regions was increased from a reference of 5 to ratios of 10 and 13, respectively, aiming to decrease the recombination losses at the front surface of the cell. As a result, the SE structure had a considerable impact on the performance of the PERC cell. Upon increasing the ratio of the n+/n++ regions from 5 to 13, the open-circuit voltage (Voc) increases considerably, except for the fill factor (FF). The decline in FF for SE PERC was due to the higher sheet resistance in the area for the n+ regions during the etch-back. The improved Voc is due to a lower Auger and Shockley–Read–Hall recombination at the front surface of a cell, and the enhanced performance of the PERCs. This confirms that the range of n++ regions should be narrower to increase Voc and reduce the Auger recombination, which is a dominant recombination mechanism. The experiment results of the PERCs were modeled using the PC1D simulation program to calculate and compare the influence of the local contact pattern and SE structure on Voc. The calculation using a two-diode model indicates that the recombination current for SE PERCs occurs in the depletion region of the pn-junction. The results suggest that an improvement of the emitter through an SE structure with a narrower range of n++ regions is essential for improving the conversion efficiency of industrial-sized PERC solar cells.

35th European Photovoltaic Solar Energy Conference and Exhibition; 270-272, Surface band bending evaluation by assessing Terahertz (THz) emission from silicon wafers using a laser terahertz emission microscope (LTEM) is systematically and quantitatively compared with the non-contact voltagecharge (V-Q) method which utilize a Kelvin probe. The amplitude of THz emission consistently changed with the surface barrier voltage Vsb of non-contact V-Q when the surface was depleted or weakly inverted. The deposited charge density required to zero THz amplitude was close to Qtot of noncontact C-V, the charge needed to move the surface from initial condition to the flatband. When the surface had accumulation layer, the THz emission showed sensitivity to the surface charging, while Vsb = 0 and was insensitive to the surface charging. The amplitude of THz emission saturated when the surface was strongly inverted or accumulated. The results show that the LTEM can be a tool similar to the non-contact V-Q in combination with a corona charging. Furthermore, the sensitivity of THz emission to the both of depleted and accumulated surface suggests that the LTEM can be a tool to evaluate surface field of silicon surfaces to which corona charging is not applicable.

35th European Photovoltaic Solar Energy Conference and Exhibition; 574-576, In this study, effects of light absorption from rear side were investigated in bifacial interdigitated-back-contact (IBC) silicon solar cell. Our bifacial IBC solar cell has a front surface field (FSF) and screen-printed electrodes. A conversion efficiency of 19.7% was obtained from front side illumination with black sheet under the cell. When white sheet was placed under the cell, a conversion efficiency of 20.6% was obtained. These results indicate that bifacial IBC solar cells have the potential to fabricate two types of modules according to the condition of installing the modules. In the case of low absorption expectancy from the rear side such as residential space, a high reflectance back sheet under the cell would lead to a high-output as a one-sided absorption module. When set in a place with high absorption expectancy from the rear side such as PV plant, our bifacial module will lead to high output. The internal quantum efficiency (IQE) spectrum and mapping analysis showed that further improvement could be obtained to suppress the carrier collection loss at the BSF region, especially busbar area. The busbar regions in both emitter and BSF act as low carrier collection centers. Thus, the Jsc of our cell is still low. The ratio of busbar electrodes on emitter and BSF region is approximately 7 % with respect to the cell area. By eliminating the busbar region, we expect to increase the Jsc by approximately 1 mA/cm2, which should lead to over 21% conversion efficiency.

35th European Photovoltaic Solar Energy Conference and Exhibition; 503-506, We developed a diamond wire characterized by the core steel-wire diameter of 80 μm and the size of diamond abrasives ranging from 6 to 12 μm (labelled as 80d-M6/12). The diamond particles on the wire are designed to have lower density and less agglomeration than those on conventional wires. As-developed diamond wire is introduced into multi wire saw to cut monocrystalline silicon bricks into wafers with a thickness of 210 and 140 μm. The above wire allows us to reduce the silicon dust or kerf to 100 μm per wafer. After as-sawn wafers are separated from fresh and worn-out wire sides of bricks and labelled as fresh and worn-out wire side wafers. In three-line bending test, a variable load is applied in perpendicular direction to wire saw marks on the wafer surface. The fracture strength distributions are evaluated on fresh and worn-out wire side wafers. In thick wafers, the fracture stress distributions are approximately the same on both sides. On the other hand, in thin wafers, the fracture strength is extremely lower than that of thick wafers. And particularly, the strength of fresh wire side wafers is lower compared to that of worn-out wire side wafers. In thin wafers, a small variation in the surface and subsurface damage is a crucial factor to decide their fracture strength of both-side wafers. In case of thick wafers, a small variation in the surface and subsurface damage may not have strong influence on their fracture strength of both-side wafers.

35th European Photovoltaic Solar Energy Conference and Exhibition; 20-22, Low concentration multi-junction (MJ) solar cells have a practical solution to consist with high efficiency and low cost. We have demonstrated a low concentration InGaP/GaAs//Si 3-junction solar cell with 23.74% at 8.0 suns using Smart Stack technology, which is a unique mechanical technology with Pd nanoparticle alignment. In this report, it is focused on the reduction of the bonding resistance. Especially, the bonding resistance at Pd/Si interface had become an important issue for low concentration performance. We examined the surface treatment of Si cell using Buffered Hydrogen Fluoride (BHF) solution. As a result, the bonding resistance at the high current density is reduced, and cell performance for low concentration was improved drastically. Using this technology, we fabricated an InGaP/GaAs//Si 3-junction solar cell and observed the maximum efficiency of 28.68% at 10.3 suns (AM1.5g). These results strongly suggested the high potential of our Smart Stack technology to achieve high efficiency GaAs//Si MJ solar cells for practical use.

35th European Photovoltaic Solar Energy Conference and Exhibition; 314-317, Currently, monocrystalline CZ silicon ingots manufactured as photovoltaic applications are all those having long straight bodies. After heat treatments in cell fabrication process, ring-type defects, well-known to lower cell efficiency, are often observed in wafers taken from seed-side position of the long crystals. On the other hand, lower density of defects in wafers taken from tail-side position is observed. The difference in the defect density results from that of thermal history during the crystal growth process in a CZ puller. We have developed special silica crucible (called liquinert crucible) whose inner surface has non-wettable property at high temperatures. Using the liquinert crucible, we have challenged the growth of “massive silicon” characterized by the diameter of more than 0.7 times the crucible diameter and the very short body-length with the expectaion of reduced thermal history. Currently, using a small CZ puller, we started to grow small “massive silicon” from the melt (3 kg) in a liquinert crucible with the diameter of 165 mm. In order to clarify the effect of thermal history, we measured lifetime of each of the seed-side and the tail-side in both conventional silicon having the diameter (~80 mm) and the “massive silicon” having the large diameter (116 – 120 mm).

33rd European Photovoltaic Solar Energy Conference and Exhibition; 27-29, Low concentration multi-junction (MJ) solar cells have a practical solution to consist with high efficiency and low cost. We have demonstrated a low concentration InGaP/GaAs/Si 3-junction solar cell with mechanical stacking method. In this development, our key technology is the direct bonding using conductive nanoparticle alignment, which is named “Smart Stack” technology. Using this technology, we fabricated an InGaP/GaAs/Si 3-junction solar cell and observed the maximum efficiency of 23.74% at 8.0 suns (AM1.5g). In addition, we discuss the reliability of InGaP/GaAs/Si 3-junction solar cells showing the results of accelerated aging test and thermal cycling test. It was confirmed that our solar cells have high long-term reliability under sever conditions. Appling general lifetime estimation method with Arrhenius plot, the life time under 10 suns was estimated to be more than 1.5×105 hours at 60. These results strongly suggested the high potential of our Smart Stack technology to achieve low cost and highly reliable mechanically stacked MJ solar cells for practical use.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 534-536, We have investigated the mechanical strength of monocrystalline silicon wafers to improve the yield of photovoltaic (PV) cell fabrication process. In slicing monocrystalline silicon bricks, diamond abrasives fixed on a wire surface scratch front and backside surfaces of wafers more seriously than wafer edges. Therefore, damages and defects not at edges but on both surfaces cause a serious concern for lowering the mechanical strength. We prepared 200 and 120 μm thick wafers by cutting silicon bricks with a multi-wire saw, in which two kinds of diamond wires, the one with the abrasive-size ranging from 8 to 16 μm in diameter and the other from 6 to 12 μm were equipped. On the wire surface, the dispersion of 6 to 12 μm abrasives was improved to be larger compared with that of 8 to 16 μm abrasives. We report that the improved wire is essential to have wafers with higher mechanical strength and the reason why the wire improvement results in the strength increase.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 637-640, We fabricated the fully ion-implanted n-type passivated emitter, rear totally-diffused (PERT) silicon solar cells with elemental boron-implanted emitters and phosphorus-implanted back surface field (BSF). The commercial base n-type (phosphorus doping) magnetic field-applied Czochralski (MCZ) silicon wafers of 156 mm × 156 mm in size were used in this study. A maximum front side conversion efficiency of 20.4% was obtained. The bifacial factor rear/front of the best-performing solar cell was 93.1%. Photoluminescence (PL) images revealed the ring-like dark contrasts of the solar cells with low conversion efficiencies. The conversion efficiencies were degraded due to oxygen precipitation during the fabrication of the solar cells.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 703-706, In this work, we present n-type bifacial solar cells with a BBr3 thermally diffused emitter on the front side. Our study related mainly to the boron profiles of the front-side emitter. We optimized the front-side boron emitter by removing the boron-depleted region by means of a spin-etching technique. The boron profiles of non-etched and etched samples were examined. Passivation qualities were also studied on non-etched and etched symmetrical p+/n/p+ samples. A reduction in the emitter saturation current density J0e in the sample in which the depletion region had been etched was investigated. A high cell efficiency of 19.6% was achieved by removing the depleted region on the front side.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1390-1392, Low concentration multi-junction (MJ) solar cells have a practical solution to consist with high efficiency and low cost. This paper shows the demonstrations of low concentration GaAs/CuInGaSe(CIGSe) and GaAs/Si MJ solar cells with mechanical stacking method. Our key technology is the direct bonding using conductive nanoparticle alignment, which is named “Smart Stack” technology. The conductive nanoparticles, such as Pd, were aligned through the use of a self-assembled block copolymer template at the bonding interface. Therefore, sufficient reduction of bonding resistance and optical absorption loss can be simultaneously attained. Using this technology, we fabricated a GaAs/CIGSe 3-junction solar cell and observed the maximum efficiency of 25.3% at 5.7 suns (AM1.5g), which is concerned in proper increase of open circuit voltage (Voc) under the concentrated sun. This is the first demonstration as concentration examination for a two-terminal GaAs/CIGSe MJ solar cell. On the other hand, for a GaAs/Si 3-junction solar cell, maximum efficiency was 21.2% at 9 suns. According to our theoretical prediction, these efficiencies can be improved over 30% under the optimized structure design. The obtain results show the possibility of GaAs/CIGSe and GaAs/Si MJ solar cells as next generation solar cell.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 510-513, Terahertz emission from silicon wafers with silicon-oxide passivation lasers were measured using a laser terahertz emission microscope (LTEM) with strong correlation between THz waveform and the surface potential being observed. The surface potential were electrically tuned by an indium-tin oxide transparent electrode disk on the top and evaluated by capacitance-voltage (C-V) characteristics. The sample were excited by Ti-Sapphire laser pulses and the waveform of THz emission were measured by the THz time-domain spectroscopy techniques using LTEM. The observed waveform changed with the external bias and inverted near the flatband voltage, and changes similar to the C-V characteristics were shown in the peak amplitude. These results indicate that the LTEM can measure and map the surface band bending of Si by analysing the waveform of THz emission. We expect that the LTEM can be applied as an optical inspection tools of passivation layers of solar cells.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 2304-2306, Potential Induced Degradation (PID) occurs at mega solar power plants and is a serious problem. The mainstream approach to PID prevention is to improve anti-reflection coating to change Si/N ratios. We, on the other hand, suggest prevention with the encapsulating material. We developed the cross-linking assistant “TENASHIELD®” which improves volume resistivity of the EVA (ethylene vinyl acetate) film. Volume resistivity of the test film is more than ten times higher than EVA film containing conventional cross-linking assistants. The power output of modules equipped with EVA film containing TENASHIELD® didn’t decrease as our PID testing showed. TENASHIELD® provided superior PID prevention to EVA film. We infer that TENASHIELD® reduces the formation of voids and conductive passes when EVA film is applied in thermal cross-linking. We assume that a migration of Na ions was prevented, and PID was reduced. Conventional anti-reflection coating is effective enough for photo-voltaic cells if TENASHIELD® is used. Cost of this method may be much lower than other PID prevention methods. Thus, TENASHIELD® may contribute to the further development of mega solar power plants.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 922-924, In this paper, we present the first measurement and analysis of terahertz (THz) generation from the hydrogenated amorphous silicon (a-Si:H) passivated c-Si surface in the absence of an external magnetic field. Using laser terahertz emission microscopy (LTEM), the terahertz emission from the surface of silicon wafers with an intrinsic a-Si:H passivation layer and those with a doped a-Si:H Hit-like stack have been measured, revealing hidden information relating to surface photocharges and band-bending not detectable by other methods without metallization. We can directly observe the polarity of the charges at the interface, as well as the strength of the inherent field-effect influencing band-bending, as a result of deposition conditions and a-Si:H quality. In addition, we are able to apply LTEM to image mapping of the deposited intrinsic a-Si:H only interface, and that of the a-Si:H(i/n) stacked layers, revealing electronic features associated with surface preparation undefined from other methods such as photoluminescence.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 660-663, We investigated the impact of wet oxidation on the electrical and interface properties of aluminum oxide (Al2O3) using atomic layer deposition (ALD) and aluminum oxide/silicon nitride (AlOx/SiNx) passivation stacks on silicon. Wet oxidation has been observed to have a significant effect on the field-effect passivation, showing an increase in the flat-band voltage shift (Vfb), and on the chemical passivation, which resulted in a reduction of the interface trap density (Dit). The decrease in Dit resulted in an increase in the lifetime and open-circuit voltages (Voc). This effect may be attributed to additional negatively charged traps originating from interstitial oxygen and hydrogen in the steam during wet oxidation. These results suggest that thermal annealing under ambient humidity is desirable to improve the quality of the passivation stacks on the rear side. This leads to high-performance passivated emitter rear cells (PERC).

32nd European Photovoltaic Solar Energy Conference and Exhibition; 527-530, Two-dimensional carrier distributions in phosphorus (P)-implanted emitter and P-diffused emitter were analyzed using super-higher-order scanning nonlinear dielectric microscopy (SHO-SNDM). The carrier distribution was clearly visualized and quantified using calibration sample. P-type, n-type and depletion layer was discriminated from local capacitance-voltage characterization obtained from SHO-SNDM measurement. The n-type region and depletion layer distribution depended on the surface texture. The position of p-n junction was estimated to be near the p-type region in depletion layer. The n-type region and depletion layer in P-implanted emitter were thicker than those in P-diffused emitter. Experimental results indicate that SHO-SNDM gives the detailed analysis of carrier distribution and is useful method for evaluation of solar cell.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 804-807, We investigate the impacts of ion beam irradiation methods in processes of phosphorus (P) implantation on P-emitter silicon solar cell performance. P implanted emitter was fabricated on p-type CZ silicon wafer. Following the wafer texture, P+ ions were implanted with tilt and step-by-step wafer rotation. The textured solar cell has a three-dimensional shape of tetrahedral pyramids in surface. Incident angle of ion beam on the textured surface depends on tilt and wafer rotation. Thus, tilt and wafer rotation are the key factors of as-implantation depth profile, resulting in the improvement of cell efficiency. We found cell efficiency increased with increase of tilt angle within a range of 7° to 35°, or decreased of rotation angle within a range of 15° to 90°. Cell efficiency is 19.15% as implantation of P is performed with an acceleration voltage of 3 keV, a total dose of 4×1015 atoms/cm2, a tilt angle of 35°, and a rotation angle of 15°.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 73-75, Smart stack is a handy method to construct multi-junction architectures through the interconnection of different types of solar cells using a Pd nanoparticle array as a bonding mediator. In this study, a triple-junction cell was fabricated from a InGaP/GaAs-based double-junction and a crystalline Si-based single-junction subcell using the smart stack approach. The simplest, matured, and widely-used Al-back surface field-type structure was particularly focused on for the Si bottom cell, and despite that, a promising efficiency of 20.9% was achieved as a smart stack InGaP/GaAs/Si device [short-circuit current density (Jsc), open-circuit voltage, and fill factor, were 9.65 mA/cm2, 2.75 V, and 0.790, respectively]. The EQE analysis of the smart stack cell was also carried out, which suggested that the device performance was limited by the Jsc generated at the GaAs subcell. Therefore, higher efficiencies are feasible through a regorous design and adjustment of each subcell, especially in terms of current matching.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1033-1037, In order to improve the quality of monocrystalline PV silicon, we have developed LCZ (Liquinertcrucible- applied CZ) crystal growth method using vitreous silica crucibles whose inner surfaces have nonwettable (melt-phobic) property. We previously reported that the bulk lifetime of p-type LCZ silicon improved twice as large as that of commercially available p-type silicon due to carbon reduction. In this study, we showed that the lifetime of n-type LCZ silicon is equal to or longer than that of commercially available n-type MCZ silicon, and that also metal reduction has the high possibility to improve the lifetime, considering the incorporation mechanism from vitreous silica crucibles.

31st European Photovoltaic Solar Energy Conference and Exhibition; 312-315, We succeeded in growing CZ monocrystalline silicon crystals with a longer lifetime than previously achieved without using MCZ technique. Instead, we employed melt-phobic quartz crucibles in a conventional CZ furnace. The improved lifetime results from carbon reduction from the growing crystals.

31st European Photovoltaic Solar Energy Conference and Exhibition; 947-949, In this work, we fabricated an n-type bifacial solar and spectral characterization have been investigated for this cell and a loss has been observed on the short wavelength. This paper mainly demonstrates increase cell efficiency by optimizing the p+ emitter with a thermal grown SiO2 as well as PECVD SiNx passivation layer. P+ emitter was formed by BBr3 diffusion. Emitter sheet resistance have been optimized by modifying the BBr3 diffusion temperature. Sheet resistance ranges from 49Ω/Sq to 173Ω/Sq, diffusion depth ranges from 0.4 um to 0.8 um. By optimizing the front side emitter an improvement has been observed for short wavelength and increases the front side efficiency by 0.4%.

31st European Photovoltaic Solar Energy Conference and Exhibition; 453-456, Open-circuit voltage (Voc) of silicon solar cells enclosed in modules were evaluated by analyzing calibrated images of electroluminescence (EL), which is obtained using a InGaAs camera and a secondary radiance standard. The EL emission rate of the respective cells were acquired by spatially integrating the EL image, then analyzed using a reciprocal relationship between EL and solar cell operation, to obtain Voc at 1-sun. The resulted values agreed well with the values measured with a solar simulator within the range of uncertainty (Voc = 6.8 mV per cell, k = 2). This technique enables a quantitative evaluation of solar cells with EL imaging following graphical analysis to evaluate crack and faults, and is a promising candidate for quantitative evaluation of degradation of photovoltaic modules in solar power plants.

31st European Photovoltaic Solar Energy Conference and Exhibition; 35-38, Two-dimensional carrier distribution in a phosphorus (P)-implanted emitter is observed by scanning capacitance microscopy (SCM). The SCM image shows a clear contrast at an almost constant depth along the surface of a silicon wafer with a pyramidal texture. Segregation of carriers in convex and concave regions of the pyramidal texture was not observed. A non-monotonic SCM depth profile is discussed based on the applied bias and carrier concentration. Junction depth of top, valley, and side wall of pyramidal texture is evaluated from SCM depth profile. The junction depth of the side wall is nearly equal to that of the valley. Since the vertical junction depth immediately beneath the surface of the texture is determined by diffusion from the side wall, it is longer than those of the side wall and valley. Based on the SCM images, formation processes of p-n junction in a P-implanted emitter are discussed.

26th European Photovoltaic Solar Energy Conference and Exhibition; 1753-1756, We present a novel solar cell structure with a rear dielectric layer made of screen-printed polyimide for the first time. We propose a low-cost cell fabrication process incorporating screen-printed polyimide layers. In this process, the rear dielectric layer and contact holes can be formed at the same time by the screen-printing of polyimide ink. The rear point-contact structure can, therefore, be realized by the screen-printing without using costly processes such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) which were employed for depositing the rear dielectric layers. We report the properties of this new type of cells and show that the new material and process proposed here are promising for next generation c-Si solar cells.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 2429-2432, Recently, a fixed-abrasive wire (diamond wire) where diamond grits are fixed on the surface of a piano wire is attracting much interest because of its advantages such as a higher slicing speed of silicon (Si) ingots and a water soluble coolant (grinding fluid) without slurry. The diamond wire sawing, however, can have a problem in the production of crystalline Si (c-Si) solar cells since the surface morphology of as-sliced wafers is different from that of wafers sliced by a loose-abrasive wire. Therefore, a new cleaning and texturing technique is required. We developed the texturing process suited for the wafers sliced by a resin-bonded diamond wire and obtained a high efficiency over 17 % using the single c-Si wafers sliced by this method. It has thus been confirmed that the wafers sliced by resin-bonded diamond wires can be employed for fabricating high-efficiency c-Si solar cells when the cleaning and surface texture processes are properly optimized. The diamond wire sawing has been proved to be promising as a next generation slicing process for c-Si solar cells.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1971-1974, In this paper, spin-on doping (SOD) is investigated and applied to the fabrication of emitter layers of crystalline Si solar cells. The diffusion process and gettering effect are studied in detail and compared with those of conventional POCl3 diffusion. It has been found that the optimum diffusion temperatures for mono and multi-Si wafers exist around 870 and 850oC, respectively. The gettering effect accompanied with P diffusion corresponds to the high solar cell performances in multi-Si wafers. A novel approach of a hydrophilic surface condition after RCA cleaning is introduced for textured wafers. This method is effective in improving the homogeneity of coating and reducing the residual organic materials after diffusion. A process of O2 treatment at 600oC prior to the diffusion can further improve the solar cell performances of textured Si wafers.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1297-1300, A new slicing method using a newly developed fixed-abrasive wire saw was examined as a replacement for the conventional method of slicing silicon ingots using loose-abrasive. The fixed-abrasive wire has abrasive diamond grains fixed onto the surface of a wire core using resin. When an ingot was sliced using this wire saw at a speed 2.5-fold higher than that of the loose-abrasive method, we obtained better results: the thickness variation decreased by a factor of three, the occurrence of wire breakage was reduced, and sub-surface layer decreased by a factor of at least two. Therefore, it was demonstrated that the fixed-abrasive wire saw is effective for slicing silicon ingots.