Spatial Characterisation at CREST

Aim

The aim of this work is to develop enhanced spatial characterisation tools for PV devices to improve the understanding in PV device degradation and fault development, which helps in improving photovoltaic module quality and reliability and ultimately can reduce energy yield uncertainty.

Research development

The characterisation tools in development consist of three main parts:

  1. A measurement system that combines multiple none-destructive spatially resolved measurement methods into one. This includes camera-based Electroluminescence (EL) imaging, spectrally resolved EL, Laser-Beam-Induced-Current (LBIC) mapping and localised spectral response (SR).
  2. An image analysis and processing tool which is used to prepare the EL image data for the simulation and modelling tool. Furthermore, its aim is to scan EL images for defects and non-uniformities. Those areas are then measured with more precision using spectrally resolved EL, LBIC and localised SR.
  3. A Simulation and modelling tool is developed to extract as many spatial device characteristics as possible from the measurements taken, as such as voltage and current distribution, temperature distribution and series and parallel resistance maps. Those simulations are to determine localised changes in the device during the aging process.

Main findings/impact

A small area measurement tool that combines EL imaging with spectrally resolved EL has been developed. The camera-based EL system is used to image the intensity of radiative recombination of the PV device spatially resolved over its full area and a monochromator-based system is then utilised to measure localised emission spectra at given points of interest identifying defects and cracks.

A large area EL imaging system has been developed to accommodate measurements of full size modules. The design of the system allows for easy extension, to for example include localized spectrally resolved EL.

The image processing tool corrects for distortions in the image taken by the camera and the actual emitted EL from the sample to improve the accuracy of simulations and detection of defects and areas of non-uniformity.

The modelling tool developed is capable of simulating the spatial voltage and current distribution of a solar cell or module. It utilises a unique photovoltaic-oriented nodal analysis method which optimises simulations and vastly reduces their execution time compared to conventional tools.

spatChar_bliss_1

Simulation tool model of a cell with 4×4 subcells; the size of the subcell array is variable dependent on required resolution

spatChar_bliss_2

Small Area combined measurement system for measuring small devices up to 160x160mm

Contact: Martin Bliss

Publications