The poor short-wavelength response of nearly all PV technologies can be improved via luminescent down-shifting (LDS) of the high energy photons present in sunlight to visible wavelengths where the PV devices exhibit very high response. This requires the incorporation of a LDS layer above the solar cell(s) in the architecture of a PV module. A pre-existing layer, such as the EVA encapsulant for silicon PV, can be used to host the luminescent species. Alternatively, a new add-on layer can also be added.
Figure: External quantum efficiency (EQE) curves for multi-crystalline silicon mini-modules exhibiting the enhancement of the short-wavelength response in the region 300-400 nm.
The use of luminescent materials with visible wavelength emission results in colouration of PV modules. This property is of particular interest for applications where aesthetics are important, such as building-integrated PV (BIPV).
Figure: Three differently coloured CdTe mini-modules using LDS add-on layers.
Contact: Efthymios Klampaftis
Down-Conversion (DC) otherwise known as quantum-cutting of a high energy photon to two lower energy photons can lead to significant gain in PV module efficiency. Our research focuses on using suitable lanthanide ion pairs that can be integrated in the PV module architecture.
Figure: The in-principle potential of the DC technology to result in external quantum efficiency (EQE) values in excess of 100% is shown for a luminescent material embedded in EVA encapsulation layer, which absorbs in the 300-500 nm region and emits with 200% PLQY.
Contact: Efthymios Klampaftis, Bryce S. Richards
PV modules are transparent to photons with lower energy than the semiconductor’s bandgap. At IMT we develop materials that can perform up-conversion (UC) with high efficiency and the methodology to integrate UC layers to PV modules.
Figure: Schematic depicting an UC layer placed at the back of a silicon solar cell and concentrating lenses for increasing the local intensity of NIR photons incident to the UC layer.
The luminescent solar concentrator (LSC) is a low concentration technology that has the potential to lower the cost of solar electricity by using inexpensive materials. The LSC is a particularly promising technology for the urban environment, as it offers a great degree of flexibility in shape, colour and system design. At IMT we investigate ways to increase the LSC efficiency and upscale the technology.
Figure: A large-area (60 cm ͯ 60 cm) LSC in a flash solar simulator for electrical characterization.
Contact: Efthymios Klampaftis
Soiling of PV modules decreases their electrical output and increases their operational cost of PV installations. To address this issue, we are investigating the use of bio-inspired self-cleaning cover layers. By nano-/micro structuring the surface of polymers, it is possible to achieve superhydrophobicity leading to self-cleaning functionality. At the same time, by optimizing the aspect ratio of the nano/micro structures, reduction of reflection and better light management can be achieved, leading to higher energy conversion efficiency.
Figure: A water droplet on a structured fluoropolymeric layer exhibiting a contact angle of >160°.
A major challenge towards commercialization of perovskite solar cells (PSCs) is their stability under prolonged exposure to environmental conditions, including ultra-violet (UV) light and ambient moisture. The aim of this project is to achieve long lifetime of PSCs by developing a suitable encapsulation scheme that will both prevent the ingress of water as well as convert the UV photons to visible wavelengths by means of luminescent down-shifting.
Figure: Schematic depicting three degradation sources for perovskite solar cells: moisture, light and temperature.