’Grätzel’ solar cells achieve a new record

Grätzel cells installed at the SwissTech Convention Center (credit: Alain Herzog) - Scientists at EPFL have increased the power conversion efficiency of dye-sensitized solar cells ("Grätzel cells") beyond 15% in direct sunlight and 30% in ambient light conditions. Mesoscopic dye-sensitized solar cells (DSCs) were invented in 1990s by Brian O'Regan and Michael Grätzel, taking on the latter's name - the world-famous Grätzel cells. DSCs convert light into electricity through photosensitizers - dye compounds that absorb light and inject electrons into an array of oxide nanocrystals which subsequently are collected as electric current. In DSCs, photosensitizers are attached ("adsorbed") to the surface of nanocrystalline mesoporous titanium dioxide films that are imbibed with redox active electrolytes or a solid charge-transport material - the entire design aims to generate electric power by moving electrons from the photosensitizer towards an electrical output like a device or a storage unit. DSCs are transparent, can be fabricated in multiple colors for low cost, and are already being used in skylights, greenhouses, as well as glass facades, such as those adorning the SwissTech Convention Center. In addition, lightweight flexible versions of DSCs are now commercially sold on a large scale for electrical powering of portable electronic devices such as earphones and e-readers, as well in the Internet of Things by using ambient light. Recent advancements in photosensitizers and other components of DSCs have improved the performance of DSCs under both solar sunlight and ambient light conditions.