F R A U N H O F E R C E N T E R F O R S I L I C O N P H O T O V O LTA I C S C S P
BENCHMARKING LIGHT AND ELEVATED TEMPERATURE INDUCED DEGRADATION (LETID) R. Gottschalg1, M. Pander1, M. Turek1, J. Bauer1,2, T. Luka1, C. Hagendorf1, M. Ebert1 1Fraunhofer
Center for Silicon Photovoltaics CSP Otto-Eissfeldt-Strasse 12 | 06120 Halle (Saale) | Germany Telephone +49 (0) 345 5589-5001 |
[email protected] 2Anhalt University of Applied Sciences, Bernburger Str. 55, D-06366 Köthen, Germany
MOTIVATION
RESULTS
◼ Passivated Emitter Rear Contact (PERC) Solar Cells are rapidly gaining market share → ITRPV predicts market share >50% in 2024 [1]
◼ two module types had negligible LeTID (multi-Si as well as mono-Si)
◼ Recent research results [2]-[4] showed that PERC cells may be susceptible to new kind of Light Induced Degradation (LID) → testing at higher temperatures (T > 50°C) of PERC devices resulted in much higher degradation levels (up to 10 %) → slower degradation compared to B-O-LID → not covered by IEC Standard
◼ Multi-Si modules: < 2 % LeTID power loss ◼ Mono-Si modules: up to 6 % LeTID power loss ◼ Power loss of modules from same manufacturer can scatter, but most are close to each other ◼ Checkerboard pattern in EL due to different susceptibility of individual cells can be observed
◼ How significant is this for modules currently in the market?
APPROACH ◼ Nine PERC-module types procured from various wholesalers
Power loss
Multi Multi-1 M1 Multi-1 M2 Multi-2 M1 Multi-2 M2 Multi-3 M1 Multi-3 M2
1
Power loss during LeTID test after Precon
0 -1
PMPP [%]
◼ 6 mono-Si module types ◼ 3 multi-Si module types ◼ Initial quality check for all modules
-2
Mono
-3 -4
◼ Visual inspection, EL imaging, STC measurements
-5
→ verification that no idiosyncrasies present
-6 -7
◼ LeTID test scheme has been defined based on extensive cell studies and current state of the art ([2]-[6])
0 100 200 300 400 500 600 700
time [h]
◼ LeTID testing after BO-LID stabilization
Mono-1 M1 Mono-1 M2 Mono-2 M1 Mono-2 M2 Mono-3 M1 Mono-3 M2 Mono-4 M1 Mono-4 M2 Mono-5 M1 Mono-5 M2 Mono-6 M1 Mono-6 M2
◼ Realistic carrier injection levels ◼ Intermediate temperature range, i.e. 75°C, to avoid non-LeTID degradation effects → LeTID reliably detected by these test conditions EL, 0.85 A (Mono-6 M1, initial)
◼ Current injection with I = ISC (~ 9 A) ◼ Module temperature: 25°C (± 6 K realized)
Precon
◼ Treatment time: 168 h with periodic I-V measurements
EL, 0.85 A (Mono-6 M1, after LeTID)
CONCLUSIONS ◼ LeTID test conditions were verified that reliably could differentiate modules prone to this aging mechanism ◼ Commercially available mono-Si PERC modules show high LeTID ◼ LeTID-specific test standards necessary → incorporation into IEC standard ◼ LeTID yield loss assessment necessary for Installer/Financier/Owner
◼ Current injection with I = ISC – Impp (~1 A) ◼ Module temperature: 75°C (± 2 K realized)
LeTID
◼ Treatment time: 690 h with periodic I-V measurements (1 week interval)
Benchmarking scheme – dark climate chamber
◼ Module manufacturers buying cells on stock market should test for LeTID if they want to avoid warranty cases ◼ Diagnostic and non-destructive tests required but available
LITERATURE [1] ITRPV 2017 [2] Ramspeck, Light Induced Degradation of rear passivated mc-Si solar cells, 27th PVSEC, 2012 [3] F. Kersten et al., Degradation of multicrystalline silicon solar cells and modules after illumination at elevated temperature, SolMat 142 (2015) 83-86 [4] Fung et al, Ener. Proc. 124 (2017) [5] T. Luka et al, “Intra-grain versus grain boundary degradation due to illumination and annealing behavior of multi-crystalline solar cells”, Sol. Ener. Mat. & Sol. Cells 158 (2016) [6] Fertig - Mass production of p-type Cz silicon solar cells approaching average stable conversion efficiencies of 22%, Ener. Proc. 124 (2017)
