Thin-film Modules Research Articles

Optimization of Cd1−yZnyS buffer layer in Cu(In,Ga)Se2 based thin film solar cells

SCAPS one-dimensional simulation program was used to investigate the performance of thin film photovoltaic solar cells based on Cu(In,Ga)Se2. First, the effect of CdS buffer layer thickness on the CdS/CIGS solar cell output parameters was carried out and its optimum value was determined. Subsequently, Cd1−yZnyS was introduced as alternative for CdS buffer layer and the influence of Zn content (y value) on cell performance was investigated. The optimum value of Zn content was found at 0.2, corresponding to a conversion efficiency of around 21.32%. At the end, the optimum thickness of new buffer layer was found out. Results show that CdZnS/CIGS cell with 28 nm-thick of Cd0.8Zn0.2S have 21.67% conversion efficiency with acceptable VOC and JSC values.

Superlattice-based thin-film thermoelectric modules with high cooling fluxes.

In present-day high-performance electronic components, the generated heat loads result in unacceptably high junction temperatures and reduced component lifetimes. Thermoelectric modules can, in principle, enhance heat removal and reduce the temperatures of such electronic devices. However, state-of-the-art bulk thermoelectric modules have a maximum cooling flux qmax of only about 10 W cm−2, while state-of-the art commercial thin-film modules have a qmax <100 W cm−2. Such flux values are insufficient for thermal management of modern high-power devices. Here we show that cooling fluxes of 258 W cm−2 can be achieved in thin-film Bi2Te3-based superlattice thermoelectric modules. These devices utilize a p-type Sb2Te3/Bi2Te3 superlattice and n-type δ-doped Bi2Te3−xSex, both of which are grown heteroepitaxially using metalorganic chemical vapour deposition. We anticipate that the demonstration of these high-cooling-flux modules will have far-reaching impacts in diverse applications, such as advanced computer processors, radio-frequency power devices, quantum cascade lasers and DNA micro-arrays.

Performance Evaluation of Two Photovoltaic Cell Technologies in Fluctuating Weather Conditions, Using EN50530 Test Procedure

Generally, photovoltaic (PV) cell manufacturers provide technical information, at standard test conditions (STCs) and nominal operating cell temperature (NOCT) ratings. However, this information is not sufficient to accurately predict the module operations under dynamic weather. In this study, test is conducted under fluctuating irradiance conditions, provided by EN50530 test procedure, to evaluate the performance of multi crystalline silicon and thin-film PV cells. Particular attention is given to the influence that the level and the slope of irradiance change have on the energy yield of PV technologies. This analysis aimed at revealing the appropriate selection of PV technology for obtaining maximum power under dynamic weather conditions.

Flux-boosted coating of idiomorphic CuInS2crystal layers on Mo-coated glass substrate

Cu–In–Ga–S–Se (CIGSSe) is a promising light-absorber in thin-film photovoltaic cells, as well as a photocathode for solar H2 production, but the fabrication of layers of CIGSSe crystals on substrates is both time- and cost-intensive. Here, we report the fabrication of CuInS2 crystal layers on various precursor-loaded Mo/soda-lime glass (SLG) substrates using a flux coating method. X-ray diffraction analysis indicated that the main phase was CuInS2, while MoS2 which formed through the sulfurization of the Mo substrate was present as a minor phase. Top-surface field-emission scanning electron microscopy (FE-SEM) images indicated that the CuInS2 crystals were sparsely formed on the bare Mo/SLG, In/Mo/SLG, and Cu/Mo/SLG substrates. In contrast, closely packed CuInS2 crystals were formed on Cu2S/Mo/SLG. Smaller CuInS2 crystals 0.5–1 μm in size were grown on Cu2S/Mo/SLG compared to those on other substrates. This sharp difference in crystal population and size could be attributed to the pre-loading effect of the precursors. Cross-sectional FE-SEM analysis with energy-dispersive X-ray spectroscopy mapping revealed the homogenous fabrication of idiomorphic CuInS2 crystals on the partially sulfurized Mo substrate, yielding a CuInS2/MoS2/Mo heterostructure amenable to photovoltaic applications. The formation mechanism of this unique heterostructure was discussed based on the experimental results.

Molten Lead-Free Solder Deposited by Inkjet Printing for Bonding of Thin-Film Solar Cell Modules

Molten Lead-Free Solder Deposited by Inkjet Printing for Bonding of Thin-Film Solar Cell Modules

FEM Stress Analysis of Interfacial Failure of Multilayered Thin Film Structures in Nanoscratching

Precision grinding of a multilayered thin film solar panel is recognized as the bottleneck in its manufacturing process. A primary challenge is the significantly high stress induced at the thin film interfaces during grinding. Such stress concentration can result in interfacial delamination between two dissimilar materials and thus device malfunction. This study used a finite element modelling analysis to understand the stress evolution of the multilayer thin film structure during a single grit scratching that simulates the individual interaction between abrasive grits and work materials in grinding. The results demonstrated that significant tensile and shear stresses were formed at interfaces during scratching, which could be traced back to the experimental evidence obtained from the nanoscratching process. The maximum stresses undertaken by the interfaces were simulated.

Rapid vapour deposition and in situ melt crystallization for 1 min fabrication of 10 μm-thick crystalline silicon films with a lateral grain size of over 100 μm

We developed a film deposition method which yielded continuous polycrystalline Si films with large lateral grain sizes of over 100 μm and thicknesses of ∼10 μm in 1 min on growth substrates other than silicon wafers in a single-step process. The silicon source is heated to ∼2000 °C, much higher than the melting point of Si, which enables a high deposition rate. Controlling the temperature of the growth substrate, initially above and later below the melting point of Si, allows the seamless lateral to vertical growth of crystalline silicon grains. Thermally and chemically stable substrates of quartz glass and alumina with a 0.1 μm-thick amorphous carbon layer were effective; liquid silicon wetted well by forming a thin SiC interlayer while substrates stayed stable. Such large-grain polycrystalline silicon films synthesized rapidly in 1 min may be used for low-cost, stable and flexible thin film photovoltaic cells.

An Accurate Modeling of Different Types of Photovoltaic Modules Using Experimental Data

In this paper an approach to model different types of PV modules using single diode model is presented. The proposed method utilizes the characteristics of diode ideality factor, shunt resistance and series resistance independently for developing accurate solar PV model. Apart from this, the proposed model utilizes experimental values obtained from the solar array simulator for validating the proposed approach. The procedure mainly focuses on developing an accurate method for thin film solar modules using a simplified approach. The proposed model is implemented in MATLAB and is verified with existing model. The experimental results are obtained from a 2 Kw CHROMA solar array simulator.

Simulation of a thin film solar cell based on copper zinc tin sulfo-selenide Cu2ZnSn(S,Se)4

The aim of this work is to do a simulation of a Cu2ZnSn(S,Se)4 thin film photovoltaic solar cell to link the characteristics of this cell with the materials parameters in order to improve its performances. It is found that, the cell performances are almost invariables while the thickness of the buffer layer is equal to or less than the space charge zone width of its side. But, as soon as it exceeds this width, a slight reduction in these performances is observed. However, the absorber layer thickness must have a value at least equal to the space charge region width of its side and at most equal to the sum of this space charge region width and the electrons diffusion length. An optimum value of the absorber band gap around 1.5 eV is obtained. This value is the compromise between the decreases of the short circuit current density and the increases of the open circuit voltage with the increases of the gap. This leads to a maximum cell efficiency of 12.1%.

Simultaneous shunt protection and back contact formation for CdTe solar cells with single wall carbon nanotube layers

Thin film photovoltaic (PV) devices and modules prepared by commercial processes can be severely compromised by through-device low resistance electrical pathways. The defects can be due to thin or missing semiconductor material, metal diffusion along grain boundaries, or areas containing diodes with low turn-on potentials. We report the use of single wall carbon nanotube (SWCNT) layers to enable both protection against these defects and back contact formation for CdTe PV devices. Samples prepared with a SWCNT back contact exhibited good efficiency and did not require shunt protection, while devices prepared without shunt protection using a standard metal back contact performed poorly. We describe the mechanism by which the SWCNT layer functions. In addition to avoiding the need for shunt protection by other means, the SWCNT film also provides a route to higher short circuit currents.

Survey of potential-induced degradation in thin-film modules

Two CdTe and two copper indium gallium (di)selenide (CIGS)-type modules were tested for potential-induced degradation (PID) with positive and negative 1000 V biases applied to the active cell circuit in an 85°C, 85% relative humidity environmental chamber. Various degradation mechanisms could be seen with signatures such as shunting, transparent conductive oxide (TCO) corrosion, charge carrier lifetime reduction, and dead active layer at edges along with resulting cell mismatch. All modules tested exhibited degradation by system voltage stress in chamber, but only one module type has degraded in parallel field tests. I−V curve data indicated that one CdTe-type module sequentially exhibited shunting followed by a recovery and then series resistance losses. This module type showed TCO delamination from the glass in the environmental chamber tests and also exhibited power degradation within 5 weeks in field tests. Relative rates of Coulomb transfer from the voltage-biased active cell circuit to ground are compared for the modules in chamber tests to those placed outdoors under system voltage stress to extrapolate the anticipated time to failure in the field. This analysis correctly indicated which module type failed in the field first.

Molecular-weight engineering of high-performing diketopyrrolopyrrole-based copolymer bearing high π-extended long donating units

Two D–A alternating π-conjugated copolymers bearing diketopyrrolopyrrole (DPP) and sextetthiophene with different molecular weights were synthesized to investigate their physical properties and performance in thin-film transistors and photovoltaic cells. The solubility and molecular weight (MW) of these copolymers with a highly rigid backbone were improved by controlling the feeding ratio of the monomer in the polymerization mixture. These polymers exhibited high crystallinity with a predominant edge-on chain orientation on the substrate. The higher-MW P(DPP-6T)-2 copolymer displayed a higher hole mobility of 3.26 cm2 V−1 s−1 than the low-MW P(DPP-6T)-1 copolymer. Bulk heterojunction photovoltaic cells made of a blend of P(DPP-6T)-2 and (6,6)–phenyl C71–butyric acid methyl ester displayed good device performance with a power conversion efficiency of 4.68%.

Microcontact-Enhanced Thermoelectric Cooling of Ultrahigh Heat Flux Hotspots

The dissipated power of insulated gate bipolar transistor and high electron mobility transistor amplifiers is typically nonuniform, resulting in areas of elevated temperature, or hotspots, which can have very large heat fluxes, on the order of 1000 W/cm2. While various bulk cooling systems are being researched to remove large amounts of heat, they uniformly reduce the chip temperature, leaving the temperature nonuniformity. Therefore, advanced hotspot cooling techniques, which provide localized cooling, are also required to unlock the full potential of cutting edge power devices. Thermoelectric coolers have previously been demonstrated as an effective method of producing on-demand cooling for the removal of localized hotspots. However, the heat flux of the hotspots that can be cooled is limited by the maximum cooling flux of thermoelectric devices. This paper demonstrates the thermal and reliability performance of a microcontact-enhanced thermoelectric cooling configuration, which uses a contact structure etched directly out of the electronic substrate to concentrate the cooling produced by a commercially available thermoelectric module. The 22 K of cooling, resulting in a hotspot temperature rise of <6 K for a heat flux of 2.5 kW/cm2, was experimentally demonstrated using a Laird HV37 thin-film thermoelectric module with a maximum device level cooling flux of 66 W/cm2. A numerical model was created, and it is predicted that when the chip and microcontact geometry is optimized, hotspots with heat fluxes in excess of 3 kW/cm2 can be cooled by nearly 40 K, reducing the hotspot temperature rise to 0 K.

Deposition Time Effect on the Physical Properties of Cu2ZnSnS4 (CZTS) Thin Films Obtained by Electrodeposition Route onto Mo-coated Glass Substrates

Kesterite Cu2ZnSnS4 (CZTS) is a very promising absorber material for low cost and high efficiency thin film photovoltaic cells due to its direct band gap and to its high absorption coefficient. In this work, CZTS layers were deposited onto Mo-coated glass substrates using a single step electrodeposition process. Sulfurization treatment was performed under Argon atmosphere at 500°C. The effect of the deposition time in the range of 10 min- 40min was investigated. X-ray diffraction and Raman spectroscopy have confirmed the Kesterite structure of all deposited films. The surface morphology of the samples was examined using scanning electron microscopy. Cu/(Zn+Sn) of about 0.80, determined by energy dispersive X-ray spectroscopy, was reached for CZTS films electrodeposited during 30min. Photoluminescence Spectroscopy showed a broad PL band centered around 1.45eV.

OPTIMIZATION OF LASER SCRIBING IN MANUFACTURING OF THIN FILM SOLAR MODULES

The paper presents the mechanism of absorption of dual laser pulse radiation by thin film of the ZnO, a-Si:H-based solar module. The authors of this paper theoretically justify the possibility of using mode of dual laser scribing of thin-film solar module (TFSM) at production stage and consider implementation of TFSM dual laser scribing. The duality is created by an additional channel of single laser pulse delay. Optic fiber serves as the delay channel. Moreover, the authors analyze the absorption of the first and second cycle of the laser pulse by TFSM thin film. The first pulse cycle is required for heating up the film to reduce the temperature gradient during the second pulse cycle absorption. The conditions of the second cycle absorption change due to the heating up by the first one. The change of this condition for the second cycle is in the laser radiation absorption range.

Analysis and characterization of photovoltaic modules of three different thin-film technologies in outdoor conditions

The instantaneous performance ratio of thin-film photovoltaic modules of three different technologies is analyzed and characterized using contour graphs for different outdoor conditions. This parameter changes when modules are working in outdoor conditions depending on several variables. The most explanatory parameters we have found are the module temperature, the atmospheric clearness index and the solar spectral irradiance distribution; this latter has been included in the characterization using the average photon energy index as it has been identified as a good indicator of the solar spectral irradiance distribution. Moreover, the variance of instantaneous performance ratio for each studied technology has been analyzed. We can conclude that the joint use of all these parameters in contour graphs allows us to better characterize the performance of modules and to reduce the uncertainty observed in previous proposals that only use two of these parameters.

Расчет тонкопленочного термоэлектрического модуля, изготавливаемого методом импульсного лазерного осаждения

Расчет тонкопленочного термоэлектрического модуля, изготавливаемого методом импульсного лазерного осаждения

Optimal Photovoltaic Resources Harvesting in Grid-connected Residential Rooftop and in Commercial Buildings: Cases of Thailand

Photovoltaic (PV) has recently undergone impressive growth and substantial cost decreases. A single-crystal silicon (mono-Si) or polycrystalline (poly-Si) have been dominant for solar rooftop and in commercial buildings installation in the past years. However until recently thin-film PV modules both amorphous silicon (a-Si) and other non-silicon thin films technology have been advance efficiency developments with low cost. The competition of crystalline and thin film solar panel technologies drives the cost significantly decreased and helps the solar investors for a good financial profit return for a shorter time. This study by satellite-derived data, Solar GIS pvPlanner software shows that the highest output is in a-Si, CdTe and followed by CIS, and c-Si PV modules for the locations considered in this study. The average energy output of amorphous panels in residential solar rooftop installed in Bangkok has the highest values of 1,503 kWh/kWp. The average energy output of amorphous panels in commercial building installed in Chonburi province has the highest values of 1,601 kWh/kWp. The optimal inclination angle is 15° south direction in both areas. Finally, the economic assessment of solar panels is also investigated for the feasibility investment by RETscreen model.

Thermal and Electrical Effects of Partial Shade in Monolithic Thin-Film Photovoltaic Modules

Photovoltaic cells can be damaged by reverse bias stress, which arises during service when a monolithically integrated thin-film module is partially shaded. We introduce a model for describing a module's internal thermal and electrical state, which cannot normally be measured. Using this model and experimental measurements, we present several results with relevance for reliability testing and module engineering: Modules with a small breakdown voltage experience less stress than those with a large breakdown voltage, with some exceptions for modules having light-enhanced reverse breakdown. Masks leaving a small part of the masked cells illuminated can lead to very high temperature and current density compared with masks covering entire cells.

The oxidation effect of a Mo back contact on Cu(In,Ga)(Se,S)2 thin-film solar modules

We investigated the surface properties of a Mo back contact for large-area thin-film solar modules with high efficiency and good adhesion between Mo and the absorber layer. It was determined that the appropriate surface properties of Mo would improve the efficiency from 10% to above 15.0±0.21% and narrow the efficiency distribution in large-area modules. The Mo back contact was annealed at various temperatures between room temperature and 230°C in air to control the amount of sodium diffusing from the soda-lime glass substrate during selenization and sulfurization, and to improve the uniformity of the unit cell. Before the heat treatment, the amount of sodium in the patterned area of the unit cell was more than 10 times of that in the central area of the cell. The patterned region with higher Na content had smaller grains than those in the central area with less Na, resulting in many peel-offs and shunting paths. The difference in sodium content was reduced after heat treatment. The optimized surface oxide of the Mo back contact had a thickness of around 3–5nm and consisted of the MoO3 phase. The grain boundary of Mo columnar structure near the surface consisted of the oxide layer.