Photovoltaic Module Characterization using Electroluminescence J.L. Crozier, E.E. van Dyk, F.J. Vorster Energy Postgraduate Conference 2013

Outline: Introduction to Electroluminescence (EL) imaging EL spectrum and intensity Voltage dependence of EL intensity Conclusions 2

EL Image of a Solar Cell  Cell Defects Micro Cracks Finger Defects Poor Solder/Contacts  Material Variations Multi-crystalline Silicon- Grains Edge-defined Film-fed Growth (EFG) Silicon- Striations  Material Properties (Quantitative Analysis) Voltage Dependant features Series and Shunt Resistance Wavelength Dependant features Minority carrier diffusion length/ lifetime 3

EL Emission Spectrum  The intensity of the emitted photons is related to –recombination mechanisms –material properties –optical properties –junction voltage.  The junction voltage varies across the surface of the cell but is not wavelength dependant so can be determined from a spatial EL intensity image. 4 LED Emission Spectrum Electrical Input Solar Cell Incoming Spectrum Electrical Output (Kirchartz et al., 2009).

Electroluminescence Detection EL Signal: 950 nm – 1300nm, Peak: 1150 nm Si CCD Camera: 300 nm nm (Fuyuki et. al.2009) 5

EL Intensity 6

Electroluminescence (EL) EL image highlights the following defects:  Areas of delamination  Micro cracks  Variations in cell material 7

Back Contacts EFG Material Growth Property Micro Crack Busbar Micro Cracks 8 EFG Module: EL of Cell Defects

Electroluminescence (EL) EL image highlights the following defects: Short-circuited cells Broken Fingers Cracks 9

 Electroluminescence  Quickly detects micro cracks and other cell defects  Material Properties (Quantitative Analysis)  Voltage Dependant features  Series and Shunt Resistance Wavelength Dependant features  Minority carrier diffusion length/ lifetime 10 Application of Electroluminescence Defect Identification in Photovoltaic Modules Conclusions

Acknowledgements 11 CSIR National Laser Centre, Rental Pool Programme