Kesterite Solar Cells Exceed 15% Efficiency
Scientists have achieved over 15% certified efficiency in kesterite solar cells by regulating grain growth with a new interphase material. Because kesterite is composed of earth-abundant, non-toxic elements, this advance could inform the development of more sustainable and environmentally friendly LED phosphors and emitters.
- Before this breakthrough, kesterite solar cells had remained below 13% efficiency for many years, a significant bottleneck in their development. The theoretical maximum efficiency for kesterite, according to the Shockley-Queisser limit, is predicted to be around 28%. - Kesterite's chemical structure, often abbreviated as CZTS (copper, zinc, tin, and sulfur) or CZTSSe (when selenium is included), makes it prone to defect formation during fabrication. A primary challenge is managing "antisite defects," where copper and zinc atoms swap places in the crystal lattice, which can impede performance. - A major issue limiting kesterite cell efficiency is a large open-circuit voltage (VOC) deficit, which is significantly worse than in competing thin-film technologies like CIGS (Copper Indium Gallium Selenide). This deficit is largely attributed to non-radiative recombination caused by defects and unwanted secondary phases like zinc sulfide (ZnS). - Compared to other thin-film solar cells, kesterite avoids using toxic elements like cadmium (found in CdTe cells) or scarce, expensive elements like indium and gallium (found in CIGS cells). This composition makes kesterite a more sustainable and cost-effective candidate for large-scale production. - The first kesterite solar cell, fabricated in 1997, had an efficiency of only 0.66%. The certified record of 12.6% was achieved in 2013 by researchers at IBM's Watson Research Center using a hydrazine-based solution process. - Recent advances, such as those by Professor Xiaojing Hao's team at UNSW, have involved using solution-based "molecular ink" chemistry instead of traditional vacuum-based methods. This allows for more precise control over the chemical reactions during film formation, preventing performance-limiting defects. - Beyond photovoltaics, CZTS is being explored for other energy applications. Its properties make it a candidate for use as a hole-transport layer in perovskite solar cells and for photoelectrochemical water splitting to produce hydrogen. - The name kesterite comes from a mineral first discovered in 1958 in the Kester deposit in Yakutia, Russia. In its natural form, it is a sulfide mineral with the chemical formula Cu₂(Zn,Fe)SnS₄ and is often found in tin ore deposits.
