Thin-film solar cells offer economical advantages by enabling lightweight and flexible modules. They consume less energy and fewer materials in their fabrication and yield good energy levels across a broad spectrum even in unfavorable weather conditions. Analyzing their inherent near infrared (NIR) electroluminescent (EL) radiation allows a detailed structural examination to shorten the development cycle of new module types.
Measuring the EL emission intensity provides spatially distributed details of mechanisms that could substantially diminish the power yield of a solar module. Among the causes are locally reduced diffusion lengths, micro-fissures, parallel-resistance effects, and contamination of the semiconductor layers.
According to Raf Vandersmissen, CEO of SinfraRed (Singapore), a spinoff of Xenics (Leuven, Belgium; www.xenics.com), the EL emission of thin-film cells is of very weak intensity, which in turn requires long integration times. The consequent dark current can be reduced by employing low-noise InGaAs sensors such as in the Xenics XEVA camera, and by one- or multistage thermoelectric cooling of the sensor array. This approach enables a 100-fold longer integration time and prevents weak local imperfections from going unnoticed in the noise floor.
In one test of a thin-film solar cell (left) conducted by the Photovoltaik-Institut Berlin (Berlin, Germany; www.pi-berlin.com), an EL analysis demonstrates the power loss in a solar cell due to TCO corrosion after 1000 hours of hot steam treatment (right). In this case the near 50% loss resulted from suboptimal mounting.