Archana Sinha carried out a part of her Ph.D. work at the Centre for Renewable Energy Systems Technology (CREST) in the School of Electronic, Electrical and Systems Engineering at Loughborough University from August to October 2012. The aim of her project was to compare the different spatial characterization techniques commonly used for the investigation of defects in solar cells and modules. The project structure is outlined in Fig.1. This will enable the STAPP team to build a combined characterization tool which will incorporate the best utilities of all techniques and can be used for full-scale measurement of PV devices. The specific purpose of this visit was also to create links between the two institutions which are running similar projects. The work also demonstrated using different measurement approaches and demonstratethe potential for combinatory analysis suggested here.
The following tasks have been achieved:
- Measurements on mini-modules of different technologies: crystalline and amorphous, were completed. It includes IV measurements, EQE, EL and LBIC which gives some interesting results. Some are listed below in Fig.2.
Fig.2 Dark IV, EL image and d-LBIC image of a-Si mini-module
EL measurements at different current injection levels and temperature conditions were performed to make distinction between various defects in modules. The EL image obtained with the current injection equivalent to 1/10thIsc,helped in the diagnosis of a shunted cell in module as shown in Fig.3.
Fig.3 EL images of c-Si mini-module at different current injection conditions (a)Isc, (b) 1/10th of Isc
Simulation based on 3-D distributed model was performed for thin film samples by using PSpice as well as Delphi (performed by Xiaofeng Wu) simulation software to compare the accuracy of results and computation time.Fig.4 shows that the simulated result has the similar gradient as of experimental image.
Fig.4 (a) Result obtained from PSpice simulation (3×3 subcells), (b) Experimental image of thin film mini-module