Thuwal, Saudi Arabia – A research paper published in the peer-reviewed journal ACS Energy Letters details how King Abdullah University of Science and Technology (KAUST) scientists have increased the efficiency of solar cell modules designed for use in harsh environments. KAUST’s solar cell module mitigates cell-to-module losses by rethinking the module’s optical design and the way it is stacked.
Protective enclosures designed to shield sensitive materials from harsh environments can reduce power conversion efficiency. Lujia Xu, Stefaan De Wolf, and their team at KAUST, have constructed a solar cell module with an optical design they consider more efficient.
The solar cells used by the KAUST team were made of a combination of two light-absorbing semiconductors: silicon and perovskite. Silicon is a well-established material in solar cell manufacture. Perovskite materials are less common, and more expensive, but adding a thin layer of perovskite material above the silicon can improve performance within an acceptable cost/performance ratio.
Previously, perovskite–silicon solar cells had shown efficiencies in optical-to-electrical power conversion as high as 30%, and theoretical models indicate that 45% power conversion is possible. But once the KAUST team encapsulated their tandem solar cells in a protective module, they found efficiency dropped from 28.9% to 25.7%. Their protective module was made by sandwiching the solar cells between two glass sheets, with the inside filled with TPU to encapsulate the cells.
The team believe the reduction in efficiency is the result of a refractive index mismatch after the glass and PU are applied directly on to the solar cells without cell-to-module optimisation. This results in increased reflection of incoming light.
The team opted to reduce this front reflection loss through an optical redesign of the module using refractive-index engineering. By moving a film of magnesium fluoride from the top of the cell to the top of the front glass, they reduced the refractive index mismatch, achieving efficient light in-coupling.
Xu said: ‘This simple optimisation effectively enables the highest short circuit current density – related to the maximum current that can be drawn from the device – that is reported in the literature for monolithic perovskite/silicon tandem solar modules, resulting in a power conversion efficiency increase from 25.7% to 26.2%. We now hope to explore how different materials and texturing the material surface could reduce the current losses from cells to modules even further.”