This work compares material properties of various encapsulant resins and formulations for application in glass/glass PV modules. UV weathering resulted in encapsulant discoloration and loss of optical transmittance through the coupons. This was accompanied with chemical degradation of the encapsulant, in particular at the center of the coupon. Damp heat weathering led to temporary moisture trapping within the glass/glass coupons and changes in polymer crystallinity resulting from annealing at elevated chamber temperatures, but negligible degradation of the chemistry of the encapsulants. Sequential weathering resulted in similar chemical degradation as in the UV weathering, but coupons experienced greater loss in transmittance. Out of the studied set of encapsulant types and formulations, POE encapsulants showed greater durability compared to EV As and TPOs. A change in crystallinity was observed for the TPOs that may explain the evolution of optical haze observed for those encapsulants.
The degradation of photovoltaic (PV) balance of systems (BoS) components is not well studied, but the consequences include offline modules, strings, and inverters; system shutdown; arc faults; and fires. A utility provider experienced a ∼30% failure rate in their power transfer chain, originally attributed to branch connectors. Field-failed specimen assemblies were, therefore, examined, consisting of cable connector, branch connector, and discrete fuse components. In this study, unused field-vintage specimens are examined using a benchtop prototype fixture to identify the most influential environmental stressors on BoS components as well as the effect of external mechanical perturbation. The prototype fixture was used to develop a perturbation capability for future use in the combined-accelerated stress testing chamber. The benchtop experiments were also used to develop the in-situ data acquisition of specimen current, voltage, and temperature. A significant increase in operating temperature (∼100 °C from ∼40 °C) and a different failure mode (arcing at the metal pins rather than overheating of the fuse filament) were observed promptly once periodic mechanical perturbation was applied. The current at failure was decreased from 35 A (measured for static specimens, with failure occurring in the fuses) to 15 A (for tests with mechanical perturbation, with failure at the male/female metal pin connection). After initial examination using X-ray computed tomography, the external plastic was machined away from failed specimens to allow for failure analysis, including the extraction of the internal convolute springs for morphological examination (optical and electron microscopy). Chemical composition analysis included energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy.
This study investigates the metastable defect behavior from temperature dependent current density-voltage (JVT) and capacitance spectroscopy measurements in solution-processed antimony (Sb) doped CIGS thin film solar cells. From the V oc (T) analysis, the main recombination mechanism is found to be Schottky-Read-Hall recombination in the bulk. A detailed study of the carrier concentration, defect density and energy level defects was performed using capacitance spectroscopy. Admittance spectroscopy measurements revealed an admittance step at low temperatures with an activation energy of 42 meV.
Abstract Glass/glass (G/G) photovoltaic (PV) module construction is quickly rising in popularity due to increased demand for bifacial PV modules, with additional applications for thin-film and building-integrated PV technologies. G/G modules are expected to withstand harsh environmental conditions and extend the installed module lifespan to greater than 30 years compared to conventional glass/backsheet (G/B) modules. With the rapid growth of G/G deployment, understanding the outdoor performance, degradation, and reliability of this PV module construction becomes highly valuable. In this review, we present the history of G/G modules that have existed in the field for the past 20 years, their subsequent reliability issues under different climates, and methods for accelerated testing and characterization of both cells and packaging materials. We highlight some general trends of G/G modules, such as greater degradation when using poly(ethylene-co-vinyl acetate) encapsulants, causing the industry to move toward polyolefin-based encapsulants. Transparent backsheets have also been introduced as an alternative to the rear glass for decreasing the module weight and aiding the effusion of trapped gaseous degradation products in the laminate. New amendments to IEC 61215 standard protocols for G/G bifacial modules have also been proposed so that the rear side power generation and UV exposure will be standardized. We further summarize a suite of destructive and non-destructive characterization techniques, such as current–voltage scans, module electro-optical imaging, adhesion tests, nanoscale structural/chemical investigation, and forensic analysis, to provide deeper insights into the fundamental properties of the module materials degradation and how it can be monitored in the G/G construction. This will set the groundwork for future research and product development.
Recent interest within the photovoltaic (PV) module industry is largely directed toward enhanced lifetimes in the field, balanced with improved recyclability. Traditionally, fluoropolymer-based backsheets have been used, however, are difficult to recycle. Emerging polyolefin (PO)-based backsheets are more recyclable and can be formulated to be robust. Properties of different fluoropolymer- and non-fluoropolymer-based backsheet coupons and in encapsulated silicon mini modules that have been fielded in Albuquerque, NM and Cocoa, FL are reported here. Seven backsheets were examined: two novel PO's, TPT, APO, PPE, AAA, and KPf. Methods of examination include module electrical performance (I - V flash test), surface morphology (optical microscope and gloss), polymer chemical structure (FTIR), EL imaging, mechanical tensile testing, DC breakdown voltage, DSC (phase transitions), and optical performance (reflectance spectra).
Bifacial photovoltaic modules are increasing in deployment due to advantages in energy generation, and these advanced module packaging architectures present new reliability considerations. Here, we study bifacial packaging architectures and assess the effects of module processing quality, rear-side module coverings, and polymer encapsulant chemistry on aging and degradation. We determine that mini-modules aged by accelerated testing adapted from IEC 63209-2 show similar degradation trends to nominally identical modules aged outdoors. We find lamination processing conditions have a significant effect on early degradation. We investigate degradation modes non-destructively using luminescence imaging, current-voltage performance, and external quantum efficiency. Finally, we assess chemical and mechanical characteristics of various encapsulant formulations to compare adhesion changes that may result in cell delamination.
With increasingly large-scale deployments of photovoltaic (PV) modules to meet global energy demands, interest in better establishing modules' lifespans is growing. We report on the performance of co-extruded polyolefin- (PO)-based backsheets as environmentally friendly alternatives to fluoropolymer-reinforced polyethylene-terephthalate (PET)-based backsheets using three hygrometric accelerated test conditions. After completing cumulative 4000 hours of aging, we analyzed data from electrical performance (I-V), surface roughness (gloss), and appearance (L, a*, b* color) characterizations to quantify degradation rates, quantify the corresponding activation energy, and cross-correlate between the characteristics examined, thereby providing insights into the relationship between physical characteristics and operating performance.
Hydrazine-free Cu(In,Ga)Se2 (CIGS) absorbers were fabricated using a low-cost atmospheric deposition method. The structural and electrical properties of thin film absorbers and the resulting solar cells processed using two different selenisation approaches were compared. A double selenisation process showed improved crystal structure compared to a single selenisation step, resulting in improved absorption throughout the spectrum and conversion efficiencies reaching 9.3%.
This work presents the use of a combined measurement system for spectrally-resolved
photoluminescence (PL), time-resolved photoluminescence (TRPL) and transient photocurrent decay (TPCD) to
characterise the physical properties of solar cells and their materials. A physical model is proposed to quantify the
localised carrier collection efficiency of solar cells from the measured localised minority carrier lifetime from TRPL
measurements and the localised minority carrier diffusion time from TPCD measurements. A single excitation laser
source is used to measure TRPL and TPCD at the same spot on the solar cell. Combined PL, TRPL and TPCD measurements are conducted on a CdS/CdTe and a CIGS sample. The resulting PL spectra for both samples show that the emission spectra can yield information on the material bandgap. TRPL and TPCD yield localised carrier lifetime
and diffusion times of τTRPL=3.91ns and τTPCD=40.5ns respectively for the CdS/CdTe sample, and τTRPL=2.45ns and
τTPCD=196.8ns respectively for the CIGS sample. The ratio between the τTRPL and τTPCD values is shown to be proportional to the localised carrier collection efficiency, yielding collection efficiencies of 21.97% and 7.93% for the CdS/CdTe and CIGS sample, respectively. The initial results show that the localised carrier collection efficiency may be affected by the sample’s metal contact configuration. In short, this combined measurement approach can offer a
novel and useful method of characterising the material quality of solar cells and the localised carrier collection efficiency of finished PV devices.
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