Sublimated thin-film CdTe photovoltaic devices with conversion efficiencies over 18% and a fill-factor greater than 79% have been repeatedly obtained using high-rate fabrication processes on ...commercial soda-lime glass substrates used in CdTe modules. Four major improvements to the device have enabled an increase in efficiency from a baseline of approximately 12–18.7%: 1) A sputtered multilayer metal-oxide anti-reflection layer; 2) total replacement of the CdS window layer with a higher bandgap sputtered MgxZn1−xO (MZO) window layer; 3) deposition of the CdTe layer at a higher thickness and substrate temperature; and 4) an evaporated tellurium back-contact. This work describes the effect of these changes on the device performance and film microstructural characteristics using various methods. Multiple devices with comparable high efficiency have been fabricated and demonstrated using methods described in this study, yielding very high efficiencies for CdTe polycrystalline thin-film photovoltaics using deposition processes and equipment in a university setting.
•This is a detailed account of fabrication process of high efficiency CdTe devices.•Highest efficiency for poly CdTe (18.7%) by any academic institution is demonstrated.•Each step leading to improvement in performance is thoroughly analyzed.•Microstructural, material and electrical characteristics of film and devices are studied.•Highest efficiency device is externally certified (ILX Lightwave, Newport).
•Materials and processes selected using selection methodology in CES software.•PIB and Silicone were the top candidates identified for edge seal material.•Polyethylene and Polyolefin suitable ...materials for inner layer laminate.•Instead of lamination, polymer extrusion and injection molding processes suitable for large scale manufacturing.•Significant cost reduction in PV encapsulation process.
Encapsulation of thin film Photovoltaic (PV) modules is critical from a long term reliability and durability perspective. Currently, the methods and materials used for encapsulation of thin film PV modules are similar to those applied to crystalline silicon technology. By performing a broad-based material selection methodology to investigate materials and processes suitable for encapsulation of thin film PV modules, there exists opportunities to decrease the cost of the module fabrication and improve reliability simultaneously. In this work, functionality of components and constraints for edge seal and interlayer laminate were evaluated. The property charts were graphically mapped and the materials were screened in CES selector software with the plastic data series package. The fabrication processes for the selected material were also assessed using the software.
Zinc telluride (ZnTe) films have been deposited onto uncoated glass superstrates by reactive radiofrequency (RF) sputtering with different amounts of nitrogen introduced into the process gas, and the ...structural and electronic transport properties of the resulting nitrogen-doped ZnTe (ZnTe:N) films characterized. Based on transmission and x-ray diffraction measurements, it was observed that the crystalline quality of the ZnTe:N films decreased with increasing nitrogen in the deposition process. The bulk carrier concentration of the ZnTe:N films determined from Hall-effect measurements showed a slight decrease at 4% nitrogen flow rate. The effect of ZnTe:N films as back contact to cadmium telluride (CdTe) solar cells was also investigated. ZnTe:N films were deposited before or after CdCl
2
passivation on CdTe/CdS samples. Small-area devices were characterized for their electronic properties. Glancing-angle x-ray diffraction measurements and energy-dispersive spectroscopy analysis confirmed substantial loss of zinc from the samples where CdCl
2
passivation was carried out after ZnTe:N film deposition.
In the manufacturing of photovoltaic (PV) modules, the lamination process can take up to 20 min to complete. In this work, new lamination processes are being developed, and have been prototyped, ...which hope to be able to cut this time down to as little as 30 s. This could provide significant savings in the cost of lamination equipment, floor space, and energy. PV modules are expected to have a lifespan exceeding 20 to 30 years. For moisture‐sensitive PV technologies, the edge seal between the two layers of glass can be the weakest point of its reliability. There is an inherent challenge when evaluating edge seal materials due to their low permeation rates. As part of Colorado State University's Photovoltaic Research and Development 2, work at the National Renewable Energy Laboratory has developed models to evaluate edge seal configurations in glass‐glass PV modules. Here, this new manufacturing process is evaluated for long‐term moisture durability. Different edge seal design options within glass–glass PV modules are explored. Most of these designs are targeting a superstrate on glass configuration, e.g CdTe, but some designs could be used on conventional crystalline Si cells. Using COMSOL finite element simulation software, we investigated the edge seal and interlayer design configurations containing silicone perimeter edge adhesive, desiccated polyisobutylene‐based edge seal, air, and polyolefin while integrating climate conditions equivalent to a hot and humid environment such as Miami, Florida. We found optimized configurations that will allow the module to prevent moisture ingress over 50 years minimizing the amount of time and material used while utilizing polymers that are easily dispensed.
In this work, new lamination processes are being developed, and have been prototyped, which hope to be able to cut this time down to as little as 30 s providing significant savings in the cost of lamination equipment, floor space, and energy. Using COMSOL finite element simulation software, we investigated the edge seal and interlayer design configurations containing silicone perimeter edge adhesive, desiccated polyisobutylene‐based edge seal, air, and polyolefin while integrating climate conditions equivalent to a hot humid environment such as Miami Florida. We found optimized configurations that will allow the module to prevent moisture ingress over 50 years while minimizing the amount of time and material used while utilizing the polymers that are easily dispensed.
•CdSeTe films deposited by sublimation have reduced Se content compared to source.•Crystallinity, photoluminescence, and morphology are affected by substrate temperature.•Source material is not ...stable, results in varying film composition/deposition rate.
The addition of selenium into CdTe to create the ternary alloy CdSeTe has been one of the most impactful advancements to CdTe-based photovoltaics in the last decade. CdSeTe/CdTe bilayer device structures have enabled a gain in short-circuit current due to the narrower bandgap of the alloy, with minimal to no loss in voltage. Intensity of photoluminescence and time-resolved photoluminescence measurements suggest this is due to an increase in carrier lifetime and concomitant greater fraction of radiative vs non-radiative recombination events which allows for a reduction in the voltage deficit. Here, we study the properties of as-deposited and CdCl2-treated CdSeTe films deposited by close-space sublimation under varying conditions from CdSeTe source charges with both 20 and 40 mol% CdSe. We find that the selenium content in the deposited films are substantially reduced from that of the source material. Additionally, deposition temperature, particularly that of the substrate, considerably affects the grain size, crystallinity, and photoluminescence of the material, illustrating the importance of source material selection and process optimization. Finally, we present evidence that the source material, and therefore the properties of the deposited films, change over time as the source material is used.
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•The bandgap of methylammonium bromide is suited for perovskite-CdTe tandems.•Low optical transmittance or haze in the perovskite layer will limit the tandem potential.•Haze in the ...perovskite layer results from film nonuniformity or wrinkling.•Reducing haze in wide bandgap perovskites is needed for efficient tandem cells.
To continue towards long-term reduction in the price of energy generated by photovoltaic (PV) solar cells, technological innovations are needed to achieve significant increases in device efficiency without increasing manufacturing costs. One approach is to utilize the existing capability to manufacture thin film CdTe PVs at very low cost and add another inexpensive thin film absorber to create a tandem solar cell to improve device efficiency. For this, a semiconductor with an optimal bandgap must be identified, along with a suitable device architecture. The wide bandgap perovskite methylammonium lead bromide (CH3NH3PbBr3, MAPBr) has a well-matched band gap of 2.3 eV for a CdTe tandem device. It can be processed at relatively low temperature, and is also suitable for CIGS and all-perovskite tandems. We fabricated MAPBr PVs and found that optical scattering, or haze, was significant in these perovskite layers. This limits the transmitted light reaching the bottom cell. The performance of a four-terminal (4T) perovskite-CdTe tandem cell was modeled using the 1D Solar Cell Capacitance Simulator (SCAPS) software package to determine how much haze could be tolerated and still achieve an efficiency boost compared to the CdTe cell.
The performance impact of multiple parameters related to the use of MgZnO (MZO) as the emitter for bilayer CdSeTe/CdTe solar cells has been investigated in detail through numerical simulations. Such ...a comprehensive study is particularly important, because while cell fabrication using MZO has been highly successful in some cases, it has been less so in others, and it has not been clear which combinations of parameter values are most effective. The parameters considered here include the recombination velocity at the emitter/absorber interface, bulk recombination lifetime, and the carrier concentrations of the emitter and absorber. The ranges chosen for the simulation parameters are those most likely to be found experimentally. The primary finding is that independent of the interfacial recombination velocity and bulk recombination lifetime, the MZO carrier density should be <inline-formula><tex-math notation="LaTeX">></tex-math></inline-formula> 10 17 cm -3 and in any case greater than that of the absorber to reduce interface recombination. At the same time, a shallow dopant the order of 50 meV or less should reduce Shockley-Read-Hall recombination in the bulk and enable <inline-formula><tex-math notation="LaTeX">V_{\text{OC}} ></tex-math></inline-formula> 1 V.
The addition of selenium into CdTe to create the ternary alloy CdSeTe has been one of the most impactful advancements to CdTe-based photovoltaics in the last decade. CdSeTe/CdTe bilayer device ...structures have enabled a gain in short-circuit current due to the narrower bandgap of the alloy, with minimal to no loss in voltage. Intensity of photoluminescence and time-resolved photoluminescence measurements suggest this is due to an increase in carrier lifetime and concomitant greater fraction of radiative vs non-radiative recombination events which allows for a reduction in the voltage deficit. Here, in this work, we study the properties of as-deposited and CdCl2-treated CdSeTe films deposited by close-space sublimation under varying conditions from CdSeTe source charges with both 20 and 40 mol% CdSe. We find that the selenium content in the deposited films are substantially reduced from that of the source material. Additionally, deposition temperature, particularly that of the substrate, considerably affects the grain size, crystallinity, and photoluminescence of the material, illustrating the importance of source material selection and process optimization. Finally, we present evidence that the source material, and therefore the properties of the deposited films, change over time as the source material is used.
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