PV Materials Research Articles

A Critical Review on Enhancement in System Performance of Flat Plate Hybrid PV/T Solar Collector System

The combined efficiency i.e. electrical and thermal of a simple flat plate solar hybrid PV/T water/air collector system is low. Therefore above systems are commercially not viable till date. To make these systems commercially viable, development in the system configurations can be done by modifying PV absorber shape, size and materials, and also by attaching various types of diffuse reflectors or flat concentrators to the sides of commercial PV module. PV absorber surface design with various configurations such as simple open air channel, single pass with rectangular tunnel, spiral flow absorber collector, thin metallic sheet suspended at the middle of air channel, fins at the back wall of an air duct etc., are used in a simple flat plate solar hybrid PV/T water/air collector systems to enhance its system performance at one sun concentration and above. This article reviews a simple flat plate hybrid PV/T water/air collector systems with and without PV absorber surface design with various configurations as discussed above. Finally effect of attaching a flat concentrators or diffuse reflectors with unglazed and glazed surface on performance of these systems is also discussed and analyzed.

Standard Characterization of Multi-junction Thin-film Photovoltaic Modules: Spectral Mismatch Correction to Standard Test Conditions and Comparison with Outdoor Measurements

AbstractMulti-junction thin-film devices have emerged as very promising PV materials due to reduced cost, manufacturing ease, efficiency and long term performance. The consequent growing interest of the PV community has lead to the development of new methods for the correction of indoor measurements to standard test conditions (STC), as presented in this paper. The experimental setup for spectral response measurement of multi-junction large-area thin-film modules is presented. A method for reliable corrections of indoor current-voltage characterization to STC is presented: results are compared with outdoor measurements where irradiance conditions are close to standard ones, highlighting ongoing challenges in standard characterization of such devices.

Photovoltaic characterization of Copper–Indium–Gallium Sulfide (CIGS2) solar cells for lower absorber thicknesses

Chalcopyrites are important contenders among thin-film solar cells due to their direct band gap and higher absorption coefficient. Copper–Indium–Gallium Sulfide (CIGS2) is a chalcopyrite material with a near-optimum band gap of ~ 1.5 eV. Record efficiency of 11.99% has been achieved on a 2.7 μm CIGS2 film prepared by sulfurization at the Florida Solar Energy Center (FSEC) PV Materials Lab. In this work, photovoltaic performance analysis has been carried out for a 1.5 μm absorber prepared under similar conditions as that of a 2.7 μm thick absorber sample. It was observed that there is an increase in diode factor and reverse saturation current density when the absorber thickness was decreased. The diode factor increased from 1.69 to 2.18 and reverse saturation current density increased from 1.04 × 10 − 10 mA/cm 2 to 1.78 × 10 − 8 mA/cm 2. This can be attributed to a decrease in the grain size when the absorber thickness is decreased. It was also observed that there is an improvement in the shunt resistance. Improvement in shunt resistance can be attributed to optimized value of i:ZnO for lower absorber thickness and less shunting paths due to a smoother absorber.

Photoluminescence Microscopy Study of Single Impurities and Defects in PV Materials

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Effect of sodium addition on Cu-deficient CuIn 1−xGa xS 2 thin film solar cells

Chalcopyrites are important contenders among solar-cell materials due to direct band gap and very high-absorption coefficients. Copper–indium–gallium disulfide (CIGS2) is a chalcopyrite material with a near-optimum band gap of 1.5 eV for terrestrial as well as space applications. At FSEC PV Materials Laboratory, record efficiency of 11.99% has been achieved on a 2.7 μm CIGS2 thin film prepared by sulfurization. There are reports of influence of sodium on copper–indium–gallium selenide (CIGS) as well as copper–indium disulfide (CIS2) solar cells. However, this is the first of its kind approach to study the effect of sodium on CIGS2 solar cells and resulting in encouraging efficiencies. Copper-deficient CIGS2 thin films were prepared with and without the addition of sodium fluoride (NaF). Effects of addition of NaF on the microstructure and device electrical properties are presented in this work.

Research in solar cell technologies at Tallinn University of Technology

The paper summarizes the results of R/D in new alternative materials and in thin film and monograin solar cells at EU Centre of Excellence in PV Materials and Devices at TUT. The defect structure of various chalcopyrite compounds (CuInSe 2, CuInS 2, CuGaSe 2, CuGaTe 2, AgGaTe 2, CuInTe 2, AgInTe 2, Cu 2ZnSnSe 4) was studied. A novel route of spray deposition was developed to prepare ZnO layers comprising nanorods as a promising material for solar cells. Technological conditions for controlled ZnS chemical bath deposition were determined. The influence of parameters of electrodeposition and annealings in different atmosphere to the composition and morphology of CuInSe 2 thin films was studied. Hybrid solar cells on the basis of CuInS 2 and CdTe photoabsorbers in combination with organic functional layers were prepared and investigated. All the obtained results were used to optimize the technology of producing solar cell structures in different designs.

Preparation of CIGSS Thin-Film Solar Cells by Rapid Thermal Processing

Rapid thermal processing (RTP) provides a way to rapidly heat substrates to an elevated temperature to perform relatively short duration processes, typically less than 2–3min long. RTP can be utilized to minimize the process cycle time without compromising process uniformity, thus eliminating a bottleneck in CuIn1−xGaxSe2−ySy (CIGSS) module fabrication. Some approaches have been able to realize solar cells with conversion efficiencies close or equal to those for conventionally processed solar cells with similar device structures. A RTP reactor for preparation of CIGSS thin films on 10cm×10cm substrates has been designed, assembled, and tested at the Florida Solar Energy Center’s PV Materials Lab. This paper describes the synthesis and characterization of CIGSS thin-film solar cells by the RTP technique. Materials characterization of these films was done by scanning electron microscopy, x-ray energy dispersive spectroscopy, x-ray diffraction, Auger electron spectroscopy, electron probe microanalysis, and electrical characterization was done by current–voltage measurements on soda lime glass substrates by the RTP technique. Encouraging results were obtained during the first few experimental sets, demonstrating that reasonable solar cell efficiencies (up to 9%) can be achieved with relatively shorter cycle times, lower thermal budgets, and without using toxic gases.

Experimental solar spectral irradiance until 2500 nm: results and influence on the PV conversion of different materials

AbstractIn this work, results are presented concerning solar spectral irradiance measurements performed in Madrid in the wavelength range 250–2500 nm, that is, extending the spectral range far away from the wavelengths where PV semiconductors are active. These data were obtained considering a horizontal receiver surface during selected clear days covering the four seasons of the year. PV materials having different spectral responses (m‐Si, a‐Si, CIGS, CdTe) have been considered to calculate spectral factors (SF) taking as reference the standard solar spectrum AM1.5 defined in standard IEC 60904‐3. From these SFs, the influence of natural solar spectral variations in PV conversion has been established. It is shown, for example, that PV technologies based on a‐Si are highly favored, from the spectral point of view, in spring–summer compared to other technologies having broader spectral responses, which are more favored in autumn–winter. From the experimental measured solar spectra, we have calculated Weighed Solar Spectra (WSS) corresponding to the four seasons of the year and also to the whole year. The WSS represents, for a certain period of time, the solar spectrum weighed over the irradiance level. SFs have been calculated for different WSSs showing spectral gains for the four PV materials during almost the full year. Otherwise, it is also shown in this work how the near‐IR part of the solar spectrum affects the evaluation of the solar resource as a whole when reference solar cells made of different PV materials are used. For typical m‐Si, a‐Si, CIGS, and CdTe solar cells, the ratio of Isc over global irradiance is not constant along a given day showing variations that depend on the season and on the PV material considered. © 2006 John Wiley & Sons, Ltd.

Hierarchy of Tools for the Characterization of Performance Limiting Defects in PV and IC Materials

not Available.

Alternative PV: Large scale organic photovoltaics

Organic/polymer PV is a promising technology that could result in low cost flexible large area solar cells. The technology is typically presented as a thin film of a light absorbing conjugated organic/polymer material sandwiched between a transparent electrode and a metal electrode. Dr Frederik C. Krebs, Riso National Laboratory, Denmark reports on this potential alternative to traditional solar PV materials constructed from inorganic semi-conducting materials.

Development of CIGS2 thin film solar cells

Research and development of CuIn 1− x Ga x Se 2− y S y (CIGSS) thin-film solar cells on ultralightweight flexible metallic foil substrates is being carried out at FSEC PV Materials Lab for space applications. Earlier, the substrate size was limited to 3 cm × 2.5 cm. Large-area sputtering systems and scrubber for hydrogen selenide and sulfide have been designed and constructed for preparation of CIGSS thin-films on large (15 cm × 10 cm) substrates. A selenization/sulfurization furnace donated by Shell (formerly Siemens) Solar has also been refurbished and upgraded. The sputtering target assembly design was modified for proper clamping of targets and effective cooling. A new design of the magnetic assembly for large-area magnetron sputtering sources was implemented so as to achieve uniform deposition on large area. Lightweight stainless steel foil and ultralightweight titanium foil substrates were utilized to increase the specific power of solar cells. Sol–gel derived SiO 2 layers were coated on titanium foil by dip coating method. Deposition parameters for the preparation of molybdenum back contact layers were optimized so as to minimize the residual stress as well as reaction with H 2S. Presently large (15 cm × 10 cm) CuIn 1− x Ga x S 2 (CIGS2) thin film solar cells are being prepared on Mo-coated titanium and stainless steel foil by sulfurization of CuGa/In metallic precursors in diluted Ar:H 2S(4%). Heterojunction partner CdS layers are deposited by chemical bath deposition. The regeneration sequence of ZnO/ZnO:Al targets was optimized for obtaining consistently good-quality, transparent and conducting ZnO/ZnO:Al bilayer by RF magnetron-sputter deposition. Excellent facilities at FSEC PV Materials Lab are one of its kinds and could serve as a nucleus of a small pilot plant for CIGSS thin film solar cell fabrication.

Large area CIGS2 thin film solar cells on foils: nucleus of a pilot plant

In earlier research, conversion efficiency of 10.4% (AM1.5) and 9.9% (AM0) has been achieved on small area CuIn x Ga 1− x S 2 (CIGS2) solar cell on 127 μm thick stainless steel substrate. The area of research is mainly focused on studying CIGS2 thin films as solar cell absorber material and growing high efficiency cells on ultralightweight and flexible metallic foils such as 127 μm thick stainless steel and SiO 2 coated 25 μm thick Ti foils. This paper presents the scaling up process of CIGS2 thin film substrate from 2.5 × 2.5 cm 2 to 10 × 10 cm 2. Initial scaling up efforts focused on achieving uniform thickness and stress-free films. Process of scaling up consisted of refurbishment of selenization/sulfurization furnace, design and fabrication of scrubber and enlargement of new CdS deposition setup. The scaling up from 2.5 × 2.5 cm 2 to 10 × 10 cm 2 substrate size has laid the foundation for PV Materials Lab of Florida Solar Energy Center becoming the nucleus of a pilot plant.

Advanced method for WWER RPV embrittlement assessment

The integrity assessment of reactor pressure vessels (RPV) is a main issue of NPP safe operation. Mechanical properties of the PV materials are degrading progressively under neutron irradiation reducing safety margins. To estimate the current state of embrittlement and to predict actual RPV safe life, it is necessary to develop improved radiation embrittlement understanding models. This is particularly true for the case of re-embrittlement after annealing, typical of several VVER-4000 RPVs. In the present work, on the base of analysis of available information, a semi-mechanistic model is offered. The model is based on the additive contribution of the three main known embrittlement mechanisms: matrix damage, precipitations and segregations which are simply described analytically since the understanding of the role P and Cu in enhancing irradiation embrittlement is rather well known. The model is used to explain and predict embrittlement and re-embrittlement after annealing of high P materials typical of certain VVER-440 RPVs. The proposed model. In this case, proves to have a very practical relevance, since it explains the peculiar re-embrittlement kinetics at low fluence after annealing. This is important for the correct interpretation of early surveillance data avoiding un-correct prediction for longer term embrittlement.

Research Trends

Is AM1.5 applicable in practice: Modeling eight PV materials Modeling of refractive index and reflectivity of quantum-well solar cell Monolithic crystalline multijunction solar cell development Characterization of modified Si solar cell emitter by porous Si layer Quality of chemical bath deposited CdS layers in thin-film PV cells Enhancing efficiency of solar cells and extending performance life

Dow Corning investigates PV materials

One of the latest large companies to look deeper into PV is Dow Corning, which says it wants to contribute to improving raw material supply availability, cost competitiveness and durability of solar PV modules sold in the ‘fast growing and innovative’ renewable energy industry. The company plans to expand its role from a supplier of raw materials, and offer a number of silicon-based solutions. This is a short news story only. Visit www.re-focus.net for the latest renewable energy industry news

Research Trends

Modeling PV materials for light intensity and two spectra, for indoor PV Monolithic dye-sensitized solar cells for stable low-power modules Nondestructive diagnostics of solar cells by modulated optical beam-induced PV signal

Characterization of direct transitions for new, high-efficiency PV materials

Characterization of direct transitions for new, high-efficiency PV materials

Novel optical characterization techniques for PV materials, devices

Novel optical characterization techniques for PV materials, devices

Solar cells: past, present, future

This paper gives an up to date perspective of PV technology and materials. The most important material has been and still is silicon. It dominates the present world market, particularly in its crystalline form but amorphous silicon is also of importance. Crystalline silicon solar cells are still heavily dependent on the materials base of the semiconductor industry. This material still has a large potential for cost reduction in its conventional form and even more so in the crystalline thin film version. Great hope rests with the thin film materials which require only small amounts of material. A great number of new concepts and materials are still in the research stage. Some of them may lead to much higher efficiency and lower cost in the coming decades. A function was identified which can be fitted to the past development of the best laboratory efficiencies. By fitting this function to the data points the future development of efficiency can be estimated for each technology.

“Through-the-glass”, double-sided laser crystallisation using copper vapour lasers for the production of thin film silicon material

Through-the-glass laser crystallisation of a-Si, on low-temperature glass, has been achieved for the first time using a copper vapour laser (CVL). The CVL's 578/511 nm output has minimal absorption in the substrate, thus allowing a simple double-sided irradiation regime. Raman spectroscopy showed that double-sided irradiation is more effective at producing full depth crystallisation, and incrementally increases the crystallisation depth with each pulse. A step-wise crystallisation concept is also introduced to explain the incremental crystallisation behaviour. Additionally, grain sizes were maintained without the need for substrate heating. These factors enhance the CVL's potential to simplify producing PV materials via laser crystallisation.