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Shingled string technology can be used to maximize the output power of photovoltaic modules. The maximum power (Pmax) of a shingled photovoltaic module can be increased by using a bifacial heterojunction with an intrinsic thin layer (HIT) of cells. To fabricate the shingled strings for a high power module, we first cut 6-inch solar cells by laser scribing while minimizing cutting loss. Unlike standard crystalline silicon (c-Si) solar cells, the structure of bifacial HIT solar cells is weak under thermal effect, so an optimal scribing condition had to be found. After laser scribing processes had been optimized, Pmax was increased by 0.02W for each separated solar cells when we using an ultraviolet (UV) laser compared to the green laser, and a UV cut shingled string of HIT cell was demonstrated for the first time.

Shingled string photovoltaic (PV) cells have a larger active area, and they significantly reduced damage from the interconnection process using electrically conductive adhesives. This new method using a shingled design provides increased PV module power compared with the conventional PV module for the same installed area. In this work, we study the optimization of shingled string PV cells for high-power shingled design modules (SDMs). To successfully fabricate shingled string PV cells and high-power SDMs, we adjusted the overlap width between solar cells and achieve conversion powers of 406.5 W for a 1100 mm × 1980 mm area. Finally, we perform a reliability tests to verify the durability of our SDMs.

This paper presents a study on the effects of heat treatment conditions on electrically conductive adhesives. Among the advantages of the shingled solar cells include larger active area and smaller current density since one of the main factors of the power loss is due to a decrease in current density. Therefore, when there is a small current, there is a benefit in regards to the power loss. The advantage of this new technique of developing photovoltaic modules is the increase of module power using the same installed area. Electrically conductive adhesives play an important role in the manufacture of shingled solar cells and understanding the effects of its curing condition is necessary to maximize its output power. Through changing the curing time and temperature, the optimized curing conditions for electrically conductive adhesives and fabricated shingled strings for development of a module could be established. Finally, we demonstrated a 500 mm × 500 mm photovoltaic module with a conventional and the other using the shingled method for purposes of comparison and a shingled module showed about 29% increase in maximum output power compared to a conventional module with the same installed area.

In the recent years, thin film solar cells (TFSCs) have emerged as a viable replacement for crystalline silicon solar cells and offer a variety of choices, particularly in terms of synthesis processes and substrates (rigid or flexible, metal or insulator). Among the thin-film absorber materials, SnS has great potential for the manufacturing of low-cost TFSCs due to its suitable optical and electrical properties, non-toxic nature, and earth abundancy. However, the efficiency of SnS-based solar cells is found to be in the range of 1 ~ 4 % and remains far below those of CdTe-, CIGS-, and CZTSSe-based TFSCs. Aside from the improvement in the physical properties of absorber layer, enormous efforts have been focused on the development of suitable buffer layer for SnS-based solar cells. Herein, we investigate the device performance of SnS-based TFSCs by introducing double buffer layers, in which CdS is applied as first buffer layer and ZnMgO films is employed as second buffer layer. The effect of the composition ratio (Mg/(Mg+Zn)) of RF sputtered ZnMgO films on the device performance is studied. The structural and optical properties of ZnMgO films with various Mg/(Mg+Zn) ratios are also analyzed systemically. The fabricated SnS-based TFSCs with device structure of SLG/Mo/SnS/CdS/ZnMgO/AZO/Al exhibit a highest cell efficiency of 1.84 % along with open-circuit voltage of 0.302 V, short-circuit current density of 13.55 mA cm−2, and fill factor of 0.45 with an optimum Mg/(Mg + Zn) ratio of 0.02.

Fabrication of Cu(In,Ga)(S,Se)2 (CIGSSe) absorber films from environmentally friendly solutions under ambient air conditions for use in solar cells has shown promise for the low-cost mass productio...

Interconnection of solar cells by an electrically conductive adhesive (ECA) can replace the use of conventional metal ribbon connections for photovoltaic module fabrication. This technology increases the active area for photocurrent generation because the cells are connected in a busbar-less structure, and high-power, high-efficiency modules can be manufactured. In this study, we investigated the influence of the curing conditions on the characteristics of the ECA film and interconnected cell. In addition, this paper presents a new method for extracting the resistance contribution of the ECA to the interconnected cell. A low sheet resistance of 60 s, regardless of the curing temperature. In addition, the sheet resistance was 60 s was required for a similar efficiency improvement at lower temperatures. Notably, the characteristics of the interconnected cell simulated using the extracted ECA resistance values were similar to the measurement results.

A tunnel recombination junction (TRJ) layer for hydrogenated amorphous silicon (a-Si:H)/ Cu(In,Ga)Se₂ (CIGS) tandem solar cells is investigated. An Al-doped zinc oxide (AZO) thin film is applied to the TRJ, and the influence of electron beam (e-beam) irradiation on defects along the TRJ is investigated. The AZO thin films are prepared using radio frequency (RF) sputtering and the e-beam is irradiated at 200 W RF power and 2 keV DC power for 5 min. In the e-beam irradiated AZO thin film, the number of oxygen vacancies and Zn interstitials increases, which in turn strengthens the effect of defect-enhanced tunnel recombination.

The shingled array of solar cells has the advantages of a larger active area and smaller current density than conventional solar cells. Because the power loss is mainly driven by the decrease in current density, this new method has the benefit of increasing module power with the same installed area as used in other methods. As the electrically conductive adhesive (ECA), CA3556HF was chosen and characterized by analysis of reflectance and sheet resistance. These analyzed data show consistent and relevant results for the cell efficiency of separated and serially connected cells fabricated by means of the shingled array method. We successfully demonstrated the increase of the high density module (HDM) power by 5.1% for a 30 cm×30 cm area and the fill factor also increased by 2% compared with conventional modules.

Transparent p-CuI/n-SiZnSnO (SZTO) heterojunction diodes are successfully fabricated by thermal evaporation of a (111) oriented p-CuI polycrystalline film on top of an amorphous n-SZTO film grown by the RF magnetron sputtering method. A nitrogen annealing process reduces ionized impurity scattering dominantly incurred by Cu vacancy and structural defects at the grain boundaries in the CuI film to result in improved diode performance, the current rectification ratio estimated at ±2 V is enhanced from ≈106 to ≈107. Various diode parameters, including ideality factor, reverse saturation current, offset current, series resistance, and parallel resistance, are estimated based on the Shockley diode equation. An energy band diagram exhibiting the type-II band alignment is proposed to explain the diode characteristics. The present p-CuI/n-SZTO diode can be a promising building block for constructing useful optoelectronic components such as a light-emitting diode and a UV photodetector.

Fabrication of Cu(In,Ga)(S,Se)

The Shingle Photovoltaic (PV) module is a new high power PV module technology manufactured by ’Dividing and ECA (Electrical Conductivity Adhesive) bonding’ method for solar cell. In the case of a general PV module, a metal ribbon is soldered on the bus bar of the solar cell and connected to others. The dividing/ECA bonding technology connects the divided cells through bonding to manufacture a string. In order to make a module, the fabricated strings must be connected with Bus ribbon. The Shingled strings produced by the dividing and bonding method are not limited to the interconnection method by the metal ribbon. Also, it is not standardized for interconnections between strings. Therefore, we analyzed the characteristics of the shingled strings according to the soldering method. The characteristics of the string vary depending on the number of metal ribbons that contact the solar cell electrodes. Experimental results show that the series resistance increases significantly with fewer contacts. As a result, the efficiency of two-point contact decreased by 0.458%, four-point contact decreased by 0.048%, and eight-point contact decreased by 0.034%. This is because as the number of contacts increases, the resistance of the busbars becomes smaller and the contact resistance becomes smaller.

Thin-film multijunction solar cells are considered to be the most promising structure for next-generation photovoltaic devices. We fabricated CuGaSe2 (CGS)/Cu(In,Ga)Se2 (CIGS) monolithic tandem solar cells. The intermediate AZO film was used as a recombination layer between the top cell and the bottom cell, and its thickness was varied from 50 to 200 nm. The best tandem cell parameters with a 50 nm thick Al-doped ZnO (AZO) layer showed a V OC = 1.03 V, J SC = 10.24 mA/cm2, FF = 41.5%, and efficiency = 4.32%. We showed the V OC of monolithic tandem cell to be over 1 V under illumination. We also observed the current continuity between the CGS cell and the CIGS cell which were connected in series as subcells. As the AZO thickness increased, the spectral response of the top cell decreased and the bottom cell was not completely saturated. The 50 nm thick AZO layer leads the CIGS bottom cell to be current-limiting, whereas the 200 nm thick AZO layer shifts the limitation to the CGS top cell. The results also showed that the In element diffusion into the CGS top absorber enhanced the electrical and optical properties of the top cell, whereas the Zn element diffusion into CIGS bottom absorber tended to degrade the bottom cell simultaneously.

The present article reports the development of flexible, self-biased, broadband, high speed and transparent heterojunction photodiode, which is essentially important for the next generation electronic devices. We grow semitransparent p-type Cu 4 O 3 using the reactive sputtering method at room temperature. The structural and optical properties of the Cu 4 O 3 film were investigated by using the X-ray diffraction and UV–visible spectroscopy, respectively. The p-Cu 4 O 3 /n-ZnO heterojunction diode under dark condition yields rectification behavior with an extremely low saturation current value of 1.8 × 10 −10 A and a zero bias photocurrent under illumination condition. The transparent p-Cu 4 O 3 /n-ZnO heterojunction photodetector can be operated without an external bias, due to the light-induced voltage production. The metal oxide heterojunction based on Cu 4 O 3 /ZnO would provide a route for the transparent and flexible photoelectric devices, including photodetectors and photovoltaics.

The periodically patterned Si nanopyramid solar cell shielded with SiN x -passivation layer was fabricated using nano-imprint method. The fabricated nanopyramid Si solar cell demonstrated the near-zero reflectivity over a wide range of wavelengths. With a SiN x -coating layer, nanopyramids showed 0.366% reflection. A SiN x -coated nanopyramid Si is efficient to improve the carrier collection for broad wavelengths due to intrinsically low light-reflection of Si nanopyramid structures. SiN x -passivation effectively controls carrier collection efficiencies of nanopyramid structures, resulting in significant improves short wavelength lights. We systematically investigated optical and electrical performances of nanoscale solar cells and suggest a route to realize high-efficient nanoscale solar cells. The importance and influence of SiN x -passivation layer and nanopyramid structure in Si based solar cell were explained in detail with optical and electrical characteristics.

A silver nanowire (AgNW)-based stacked lamination electrode was investigated for application as the top electrode in fully vacuum-free and solution-processed organic photovoltaic (OPV) fabrication. AgNW layers were stacked with an ethylene-glycol-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) layer for conductivity enhancement and uniform contact creation, and an ethylene vinyl acetate (EVA) adhesive and a polyethylene terephthalate (PET) supporting film with subsequent hot-pressing were used for complete attachment (good electrical contact). During hot-pressing at 100 °C, the melted EVA adhesive was found to create a concrete electrical contact between the lamination electrode and the underlying polymer semiconducting layer. To verify the performance of the lamination electrode, fully vacuum-free and solution-processed OPVs with the lamination electrode were fabricated and compared to OPVs with a reference evaporated metal electrode. The results revealed that the OPVs with lamination electrodes provided the best fill factor (FF) of 53% and a final photoconversion efficiency (PCE) of 2.61%, whereas the OPVs with metal electrodes provided the best FF of 64% and a PCE of 3.41%. Analytical calculations indicate that the FF loss of lamination electrode OPVs was due to higher series resistance (11.4 Ω-cm2 vs. 15.1 Ω-cm2) and higher recombination at the interface, which can be considered an ideality factor (1.7 vs. 2.7).

Chalcopyrite Cu(In,Ga)(Se,S)2 (CIGS) semiconductors are potential candidates for use in photoelectrochemical (PEC) hydrogen generation due to their excellent optical absorption properties and high conduction band edge position. In the present research, CIGS thin film was successfully prepared on a transparent substrate (F:SnO2 glass) using a solution-based process and applied for a photocathode in solar water splitting, which shows control of the surface state associated with sulfurization/selenization process significantly influences on the PEC activity. A ZnS passivation surface layer was introduced, which effectively suppresses charge recombination by surface states of CIGS. The CIGS/ZnS/Pt photocathode exhibited highly enhanced PEC activity (∼24 mA·cm–2 at −0.3 V vs RHE). The performances of our CIGS photocathode on the transparent substrate were also characterized under front/back light illumination, and the incident photon to current conversion efficiency (IPCE) drastically changed depending on the ...

A large amount of external overpotential is normally required to split water using p-type silicon (p-Si) due to the insufficient driving force between the conduction band-edge and the hydrogen evolution level. We demonstrate how inserting an Al2O3 interlayer between p-Si and the electrolyte mitigates the requirement of overpotentials. Since the Al2O3 film decreased the number of interface defect states, electrons were observed to migrate into the Si surface so that negative charges accumulated at the band-edge of silicon. This resulted in band bending enhancement and a reduction of the overpotential requirement. In our result, the overpotential of ~ 150 mV was reduced at a current density of 20 mA/cm2, and the onset voltage of ~ 70 mV was also reduced at the 1.4 nm thickness of Al2O3 interlayer.

In the development of low-cost, efficient, and environmentally friendly thin-film solar cells (TFSCs), the search continues for a suitable inorganic colloidal nanocrystal (NC) ink that can be easily used in scalable coating/printing processes. In this work, we first report on the colloidal synthesis of pure wurtzite (WZ) Cu2SnS3 (CTS) NCs using a polyol-mediated hot injection route, which is a nontoxic synthesis method. The synthesized material exhibits a random distribution of CTS nanoflakes with an average lateral dimension of ∼94 ± 15 nm. We also demonstrate that CTS NC ink can be used to fabricate low-cost and environmentally friendly TFSCs through an ethanol-based ink process. The annealing of as-deposited CTS films was performed under different S vapor pressures in a graphite box (volume; 12.3 cm3), at 580 °C for 10 min using a rapid thermal annealing (RTA) process. A comparative study on the performances of the solar cells with CTS absorber layers annealed under different S vapor pressures was cond...

We used a DC-sputtering method to deposit the precursor (Cu3Ga/In) onto Mo with 1 um thick/soda-lime glass (SLG). We moved it onto a graphite crucible for the pre-annealing process, and the pressure of the process tube was about 10 torr without Ar gas flow. The crucible in quartz tube was heated by halogen lamp to 250 degrees C for 30 min, and then raised to 550 degrees C for 10 min under a selenium atmosphere. To complete the solar cells, a buffer layer of 50 nm CdS was then deposited by chemical bath deposition (CBD), followed by a double layer (high resistivity/low resistivity) of RF sputtered i-ZnO/Al-ZnO thin films. The Al front contacts were deposited by thermal evaporator.

This study investigated CdS deposition on a Cu(In,Ga)Se2 (CIGS) film via chemical bath deposition (CBD) in order to obtain a high-quality optimized buffer layer. The thickness and reaction temperature (from 50 degrees C to 65 degrees C) were investigated, and we found that an increase in the reaction temperature during CBD, resulted in a thicker CdS layer. We obtained a thin film with a thickness of 50 nm at a reaction temperature of 60 degrees C, which also exhibited the highest photoelectric conversion efficiency for use in solar cells. Room temperature time-resolved photoluminescence (TR-PL) measurements were performed on the Cu(In,Ga)Se2 (CIGS) thin film and CdS/CIGS samples to determine the recombination process of the photo-generated minority carrier. The device performance was found to be dependent on the thickness of the CdS layer. As the thickness of the CdS increases, the fill factor and the series resistance increased to 61.66% and decreased to 8.35 Ω, respectively. The best condition was observed at a reaction temperature of 60 degrees C, and its conversion efficiency was 12.20%.

Thermally stable silver nanowires (AgNWs)-embedding metal oxide was applied for Schottky junction solar cells without an intentional doping process in Si. A large scale (100 mm(2)) Schottky solar cell showed a power conversion efficiency of 6.1% under standard illumination, and 8.3% under diffused illumination conditions which is the highest efficiency for AgNWs-involved Schottky junction Si solar cells. Indium-tin-oxide (ITO)-capped AgNWs showed excellent thermal stability with no deformation at 500 °C. The top ITO layer grew in a cylindrical shape along the AgNWs, forming a teardrop shape. The design of ITO/AgNWs/ITO layers is optically beneficial because the AgNWs generate plasmonic photons, due to the AgNWs. Electrical investigations were performed by Mott-Schottky and impedance spectroscopy to reveal the formation of a single space charge region at the interface between Si and AgNWs-embedding ITO layer. We propose a route to design the thermally stable AgNWs for photoelectric device applications with investigation of the optical and electrical aspects.

Cu(In1-χGaχ)Se2 (CIGS) films have been considered as promising materials for solar cell applications owing to high absorption coefficient, bandgap grading, flexibility, and high conversion efficiency. In particular, the bandgap grading has been widely researched as a back surface field effect to reduce the carrier recombination. Recently, the front surface field has been researched by the application of a transition metal oxide (TMO) to increase the power conversion efficiency (PCE). Among them, NiO is an outstanding TMO layer because of its wide bandgap (∼3.7 eV), stable cubic structure, the low electron affinity of 1.33–1.85 eV and p-type characteristics. Consequently, the application of the NiO layer has been researched on the CIGS solar cells as an effective electron blocking barrier, which is to suppress the carrier recombination. Even though much research has proceeded on the versatile properties of the NiO, there is rarely research to apply the NiO layer on the CIGS solar cells yet. In this study, we introduced the application of NiO layer deposition on the CIGS solar cell to improve the PCE. The NiO layer (20 nm) was deposited on the CIGS solar cell using the E-beam evaporator system at room temperature. We investigated the effect of the application of the p-NiO layer on the CIGS solar cells, comparing the efficiencies and dark J-V curves. These results are in good agreement with time-resolved photoluminescence measurements on the carrier lifetime. The PCE of the device with the p-NiO layer was measured as 16.35% and the PCE of the device without the p-NiO layer was measured as 15.81%. After the application of the p-NiO layer, we gained the improvement with 0.54% of the PCE.

New technologies to fabricate high-output power photovoltaic (PV) modules include a cell dividing and bonding technique. This technique divides and interconnects cells into a string arranged in series and in parallel to produce a module. Therefore, we designed a 3–6 dividing front electrode structure that is suitable for the shingled module. Thus, power loss was calculated based on the number of cell divisions and the number of fingers. The simulation results indicated that increases in the number of cells to be divided decreased the number of fingers exhibiting the maximum efficiency. The number of fingers optimized for division in to 5 cells was 128. Additionally, the power conversion efficiency was 17.346%, and this corresponded to the highest efficiency among various electrode structures for division from three to six solar cells. The optimized finger number for division into 3 cells was 171, and this corresponded to the lowest efficiency of 16.855%. The multi-crystalline silicon solar cells exhibiting a finger number of 100 were fabricated to compare with the simulation results. We analyzed the characteristics and obtained results that were nearly similar to those of the simulation. For application to a shingled module, a solar cell with an appropriate electrode structure was divided into 5 cells via the laser scribing system, subsequently bonded with an electrically conductive adhesive (ECA), and the characteristics were analyzed.

A tunnel recombination junction (TRJ) layer for hydrogenated amorphous silicon (a-Si:H)/ Cu(In,Ga)Se₂ (CIGS) tandem solar cells is investigated. An Al-doped zinc oxide (AZO) thin film is applied to the TRJ, and the influence of electron beam (e-beam) irradiation on defects along the TRJ is investigated. The AZO thin films are prepared using radio frequency (RF) sputtering and the e-beam is irradiated at 200 W RF power and 2 keV DC power for 5 min. In the e-beam irradiated AZO thin film, the number of oxygen vacancies and Zn interstitials increases, which in turn strengthens the effect of defect-enhanced tunnel recombination.

The CdS buffer layer was replaced by ZnS thin film due to its toxicity. In this study, ZnS thin film was deposited by CBD method, and ZnSO4 and Thiourea, which are precursors, and ammonia, a complexing agent, were optimized and analyzed. When the ZnSO4 concentration was 0.2 M, the density of the ZnS particles became high, and a uniform thin film was confirmed. Thiourea concentration was found to be uniform at 0.8 M and minimize surface cracking. Finally, the concentration of ammonia was analyzed and the most uniform thin film was identified as 2M considering growth rate and characteristics.

The CdS buffer layer is being replaced by ZnS buffer layer owing to environmental problems. The ZnS buffer layer was deposited using chemical bath deposition process. The ZnS thin film can control the Zn2+ ion by using the complexing agent. The optimized ZnS process was studied and analyzed by adding ethylenediamine tetra acetic acid(EDTA), hexamethylene tetramine(HMTA), and Tri-sodium citrate. EDTA was used for rapid deposition. The dense thin film was deposited by using HMTA and Tri-sodium citrate.

Typically, CuInSe2 (CIS) based thin films for photovoltaic devices are deposited by co-evaporation or by deposition of the metals, followed by treatment in a selenium environment. This article describes CIS films that are instead deposited by DC and RF magnetron sputtering from binary Cu2Se and In2Se3 targets without the supply of selenium. As a novel method, electron beam annealing was used for crystallization of Cu2Se/In2Se3 stacked precursors. The surface, cross-sectional morphology, and compositional ratio of CIS films were investigated to confirm the possibility in crystallization without any addition of selenium. Our work demonstrates that the e-beam annealing method can be a good candidate for the rapid crystallization of Cu-In-Se sputtered precursors.

In the solution-based preparation of CZTS (Cu 2 ZnSnS 4 ) thin films followed by a sulfurization process, a layer of MoS 2 is formed at the CZTS–Mo interface. Formation of this MoS 2 layer is mainly governed by the sulfurization process in H 2 S ambient gas rather than diffusion of a sulfur source in the CZTS film. Growth of CZTS grain and grain boundaries facilitates the formation of a MoS 2 layer in any sulfurization process. A decrease in the series resistance and an increase in the current density and solar cell efficiency were achieved through an increase in the temperature of the second sulfurization sequence in a two-step sulfurization sequence. The formation of a CZTS grain dominates the performance of CZTS thin film solar cells with a relatively thin MoS 2 layer, but the performance is degraded by an increase in recombination rate and the hole barrier effect between CZTS and Mo when the MoS 2 is sufficiently thick.

Silver (Ag) nanoparticles were formed on fluorine-doped tin oxide (FTO) coated glass substrate, and then hydrogenated amorphous silicon (a-Si:H) thin-film solar cells were sequentially fabricated. Ag nanoparticles located in the interface between the FTO and the p-layer leads to a light-trapping effect because of the strong light-material interaction in Ag nanoparticles and enhancement of the optical path length. A higher haze ratio appeared for Ag nanoparticles with larger diameters and heights, compared with the conventional type. The device with the Ag nanoparticles showed a short-circuit current density of 12.66 mA cm−2, which was 2.2 mA cm−2 higher than the device without Ag nanoparticles. Conversion efficiency increased from 4.9 % to 5.9 % by employing Ag nanoparticles with a roughness of 71 nm. The simple process makes our design useful for low-cost, high conversion efficiency thin-film solar cells.

A double textured selective emitter (DTSE) solar cell was fabricated using Si wafer. The 40 × 40 mm 2 silicon substrates were textured to form a pyramid-shaped surface, and nanowires were fabricated by a metal-assisted chemical etching process using Ag nanoparticles. All surface modifications of the micro and nanostructures were done by a wet-based process. The heavily doped and shallow emitters for selective emitter solar cells were prepared through the POCl 3 diffusion and a chemical etch-back process, respectively. The front and rear electrodes were prepared with a conventional screen printing method. The optical properties were enhanced through the double textured (DT) structure, and additional enhancement of the electrical properties was realized through the selective emitter concept. The DTSE solar cell achieved a higher conversion efficiency of 17.9% with improved absorption and short circuit current density compared to a DT solar cell.

Binary bilayer glass/Mo/In2Se3/Cu2Se precursors have been used to rapidly form CuInSe2. Considering their possible application to large-area deposition processes, bilayer precursors were deposited by sequential radiofrequency sputtering of In2Se3 and direct current sputtering of Cu2Se onto unheated, Mo-coated glass substrates. High-temperature X-ray diffraction analysis of the glass/Mo/Cu2Se sample confirmed that the as-deposited polycrystalline Cu2 − xSe phase is likely transformed to CuSe at approximately 210 °C, and then to CuSe2 at 260 °C. Further increase in temperature resulted in the peritectic decomposition of CuSe2 to CuSe (+ liquid) at approximately 330 °C, and then to Cu2 − xSe (+ liquid) at around 380 °C with the release of Se. Pre-annealing of In2Se3/Cu2Se precursors in Se environment resulted in the formation of a liquid phase, which is in equilibrium with CuSe. Rapid, thermal annealing of pre-annealed samples between 500 and 550 °C apparently enhanced grain growth and reduced the reaction time to about 3 min; this can be explained by a liquid phase-assisted grain growth mechanism.

Nanopillar-patterned Si solar cells were investigated. Ag nanoparticles were coated on a polished Si substrate as an etching mask. Reactive ion etching caused Si nanopillars to replicate in a reverse fashion on the Ag nanoparticles over a large area. The nanopillar structures efficiently reduced the light reflection on the surface and effectively drove the incident light into a Si absorber. This induced a significant enhancement of the photogenerated-current with an improved solar cell efficiency of 16.07%. The Si nanopillar-patterned solar cells showed improved carrier collection for long wavelengths; however, the surface-defect induced recombination degraded the quantum efficiency at short wavelengths. We suggest that the reduction of recombination loss should be considered for efficient nanostructure solar cells.

In-doped ZnO thin films were prepared by a sol–gel spin coating method. Since several issues with In doping have been reported, such as degradation of crystallinity and deterioration of electrical resistivity at high In-doping levels, co-doping with Ga and electron beam treatment was demonstrated in this study. When In dopant was added to the ZnO thin film at 0.5 mol%, it increased the carrier concentration, thereby reducing the resistivity of the film. In contrast, further doping by Ga in the presence of In did not significantly change the electrical properties. When electron beam treatment was conducted on ZnO films, the optical band gap was increased and the carrier concentration and mobility were increased. In particular, a 0.5 mol% In-doped ZnO that received electron beam treatment at 2 keV exhibited an electrical resistivity as low as 4.8 × 10−2 Ω cm, while 57.1 Ω cm was obtained from the pristine ZnO thin film. When the ZnO films were applied to crystalline Si solar cells, conversion efficiency significantly increased from 10.37 % for the cell with pristine ZnO thin film to 11.45 % with the In-doped and electron beam-treated ZnO thin film.

Plasmonic thin film solar cells deposited on periodically textured photonic crystal substrates have been extensively studied since the substantially enhanced light absorption. The reduction of parasitic absorption losses in the metal and spacer layers becomes one of the key issues to achieve high efficiency solar cells. Herein, plasmonic amorphous silicon (a-Si:H) flexible thin film solar cells with different thickness of oxide spacer layers are systematically investigated. An increase of the spacer layer thickness leads to an evolution in surface morphology of AZO and final devices. More intriguingly, the increase of spacer layer thickness reduces the absorption in Ag layer while induces more absorption in spacer layer. The highest light absorption in silicon layer is observed as applying 100 nm spacer layer, which is further verified by electrical measurements. Our observations demonstrate a versatile and convenient route towards rational design of light harvesting nanostructure for high performance plasmonic solar cells based on a broad range of materials.