The Universitat Rovira i Virgili leads a protocol to improve the durability of flexible photovoltaic devices

Flexible portable devices, also known as FlexPVs, have great potential in multiple applications, for example wearable technology, intelligent fabrics, curved surfaces such as car roofs or lightweight applications such as drones or aerospace transportation. In recent years FlexPVs have made great strides in efficiency, and are now able to generate levels of power very close to those of rigid solar panels. However, the lack of a standardized protocol regarding their stability and mechanical performance makes it difficult to compare and evaluate their flexibility, durability and efficiency in real-life conditions, which in turn limits their design and development.

Now, the Universitat Rovira i Virgili (URV) has led a team of 23 experts in photovoltaic energy and mechanical performance from 12 countries in designing a unified testing protocol so that flexible solar cells and panels can be evaluated in a more consistent manner. This is a pioneering protocol that "focuses on measuring efficiency over 1,000 bending cycles at a voltage of 1%, thus providing a benchmark for measuring the mechanical resistance of these devices," explained Lluís F. Marsal, a researcher at the URV's Department of Electronic, Electrical and Automatic Engineering.

This new standardized method, which has been published in detail in the journal Nature Energy, also proposes methods for assessing flexibility in different environmental conditions and the use of encapsulation to protect devices from degradation caused by humidity and temperature.

According to the research team, this new protocol will help create a standard for evaluating flexible solar devices such as photodetectors and supercondensers and thus facilitate their safe use in a wide range of applications whilst ensuring that they operate with almost the same efficacy as rigid devices.

The team of experts was led by Kenjiro Fukuda, from the RIKEN Center for Emerging Matter Science in Saitama-Japan, and Osbel Almora, Juan de la Cierva researcher at the URV and administrator of the Emerging-PV.org consortium. The research also involved Lluís F. Marsal, professor and leader of the Nanoelectronics and Photonic Systems group at the URV and pioneer in photovoltaic research on organic solar cells.

More versatility, similar efficacy

Flexible photovoltaic devices differ from rigid ones in their structure, materials and application potential. While rigid solar panels are mostly made of silicon and are placed on fixed surfaces such as the ground, roofs or terraces, FlexPVs use other materials that allow them to be much more versatile: they can bend and adapt to curved surfaces whilst losing hardly any efficacy. Moreover, they are much lighter than rigid ones and this makes them ideal for applications where weight is a limiting factor, such as drones, smart clothing, wearable medical devices or Internet of Things technology.

The mechanics of these flexible devices also allow them to withstand more extreme conditions of movement and flexibility, opening the door to applications such as aerospace transportation or vehicles with curved surfaces.

This protocol is the first attempt at standardization between the fields of photovoltaics and flexible electronics, two scientific communities that until now have had little interaction. This, therefore, is a starting point that can be adapted to other flexible devices later on. "The progress of these devices will demand new protocols with more appropriate ways of testing the stabilization, torsion and adhesion properties of the flexible solar cells of the future" the researcher concluded.