Building confidence in new photovoltaic technologies through in situ metrology during degradation testing
One of the most important barriers for commercial introduction of new photovoltaic technologies is ensuring stability and reliability of commercial products. At NPL we have developed unique facilities to investigate the degradation profiles of new PV technologies. These involve accurately controlled environments that can simulate realistic encapsulation conditions, while applying electrical measurements and spatial characterisation techniques. Environmental conditions including atmospheric composition, spectrum and intensity of illumination, and temperature can be accurately controlled. At the same time, current-voltage measurements, luminescence imaging, and photocurrent mapping of PV devices can be performed during degradation. In addition, our multispectral illumination system for PL imaging can investigate all PV device technologies, also allowing testing of different layers of tandem PV devices. Such comprehensive facility allows measurement approaches to identify degradation mechanisms that may be encountered in real applications.
We have applied our methods to different PV device material and device technologies; from studying degradation mechanisms of emerging perovskite solar cells, to investigating the reliability of new manufacturing processes of established silicon-based technologies.
Perovskite photovoltaics degradation testing
Perovskite solar cells (PSC) have attracted considerable attention in recent years due to the high efficiencies achieved, their scalability potential and the introduction of record efficiency tandem devices with a perovskite layer on top of silicon. Although the reported efficiencies and scalability approaches demonstrated show great potential for this technology, stability issues are a significant obstacle for PSC before they can compete with established PV technologies. Although efficient encapsulation offers some protection from environmental factors, encapsulation will never be perfect and through the years some permeation of oxygen and humidity into PV modules is inevitable. There are a number of critical factors for PSC degradation, and tests require accurate conditions and measurements in order to distinguish different degradation mechanisms.
Through the metrology methodologies developed at NPL, the early stages of degradation have been identified providing guidance to manufacturers on how to improve stability, and encapsulation requirements for PSCs can be defined, providing guidelines towards replicating realistic encapsulation conditions in accelerated ageing tests and helping understand achievable reliability.
Wafer passivation reliability testing
Scientific breakthroughs in silicon surface passivation have enabled commercial high-efficiency photovoltaic devices making use of the nanostructure technologies. NPL has investigated the factors that influence the passivation stability of such technologies, through degradation studies using our state-of-the-art facilities. Such studies provide valuable insights into surface passivation degradation mechanisms on nanostructured silicon surfaces and pave the way for the industrial production of highly stable nanostructured silicon devices.
The results reliability testing and characterisation under controlled environments provide insights into the degradation mechanisms of surface passivation, which is highly relevant for the solar cell industry. Understanding the physical processes of degradation contributes to the development of more advanced passivation techniques.