Characterisation of a LBIC system by scanning of silicon solar cells and modules

A laser beam induced current (LBIC) system has been used as a non-destructive characterisation tool for photovoltaic (PV) devices. It provides a detailed twodimensional map of the current signal. Each data point in the map is generated by the laser beam scanning over the devices. The signal strength depends on the response of that particular area on which the laser beam is incident, thereby reflecting the absorption and collection characteristics of that local PV area. However, the magnitude of the measured signal, induced by modulated laser, is very small. Adjustment of set parameters, measurement variables and environmental influences may affect the measurement result and thus could lead to misinterpretation. The LBIC system at the Centre for Renewable Energy Systems Technology (CREST) is analysed for reliability and optimised. It is evident that with appropriate settings under controlled environmental conditions, the system can provide a highly repeatable measurement result

Accelerated testing of performance of thin film module

There is an interest in identifying localised effects when investigating durability of devices. The combination of tests might also have an influence on test results. This is investigated for single junction amorphous silicon modules. The modules were put under accelerated testing including thermal cycling, light soaking and annealing test. I-V measurement and LBIC system as characterisation tools are used to investigate the possible degradation occurring in the devices both before and after certain stages of the test. Results have shown that there is a difference between modules which have experienced light soaking before being exposed to thermal cycling, indicating that the initial light soaking resulted in a UV activation of the material, which then changed the durability of the lamination

Structural analysis of thin film silicon PV modules by means of large area laser beam induced current measurements

The spatial variation of key properties of large area silicon thin film PV modules is investigated using a Laser Beam Induced Current (LBIC) system. The system produces a very detailed current mapping of devices, allowing the identification of spatially varying structural defects of photovoltaic modules. It allows for efficient defect detection as well as investigations of localised performance variation. In this paper, the results are shown for large area single junction amorphous silicon modules from different manufacturers that have been installed outdoors for more than two years. Several defects are identified as probable sources of poor performance and low efficiency of some devices. Some of the major contributions to these defects are likely to occur during the production process while some are developed during outdoor exposure

Energy production of single junction amorphous silicon modules with varying i-Layer thickness

The energy production of a number of single junction amorphous silicon (a-Si) solar modules with different intrinsic layer thicknesses is investigated. This has been carried out through both indoor measurement and real operating condition monitoring outdoors. After 13 months of light exposure, the fully degraded and seasonally annealed states, can be seen. The results indicate that the thinnest devices do not necessarily have the lowest degradation. The thicker devices which have higher initial efficiency, however do suffer greater efficiency degradation. Experiment also shows that energy production does not follow the initial Standard Test Condition (STC) rated efficiency as the highest can be seen in thinner modules, which initially have much lower efficiencies

Long-term performance of amorphous photovoltaic modules

This work aims to demonstrate the energy production of amorphous silicon devices through long-term monitoring. Some devices have a very high specific energy production while other does not accomplish this. The reasons for seasonal variations are investigated. Assuming that the short circuit current is mainly influenced by spectral changes allows degradation to be attributed to the fill factor. The seasonal variation of this is investigated in more detail, demonstrating differences between single and multi junction devices

Multi-layer LBIC system for thin film PV module characterisation

Several non-destructive characterisation tools - solar simulator, LBIC, thermography - are used together to investigate the performance of and locate possible defects in TF silicon PV modules of different structures. A special module is investigated where all techniques are compared and good agreement is demonstrated

Large area LBIC measurement system for thin film photovoltaic modules

A laser beam induced current system has been developed for large area thin film technology. Employing a non-destructive laser scanning approach, such a system is used as a characterisation tool that is able to perform local performance investigation and allows efficient defect detection in large scale devices. In this paper, the results are shown for large area single junction amorphous silicon modules. The scanning images reveal an inhomogeneous current signal. Cross-section analysis illustrates that in some modules, there is considerable performance variation between cells. Certain cells are nearly or completely inactive. Interconnection problems, tiny cracks and defects that cannot be detected by visual inspection can also be identified