Ternary organic solar cells: A review of the role of the third element

Incorporating a third element in the active layer of organic photovoltaic (OPV) devices is a promising strategy towards improving the efficiency and stability of this technology while maintaining relatively low costs. While ternary organic solar cells (TOSCs) have been widely studied during the last decade, there has been a meteoric rise in TOSC research after a breakthrough efficiency of 14.1% was reported in 2017. Such values of efficiency make TOSC a promising third-generation solar technology, prompting worldwide research efforts into the inclusion of a third element for high-performance TOSCs. These efforts have further boosted their efficiency, which is currently approaching 19%, and improved the stability of OPVs. This review discusses the role of the third component in improving efficiency and stability, emphasizing the period after 2016, which witnessed huge increases in efficiency and the boom that ensued. Since their introduction in 2008 for applications in photovoltaics and optoelectronics, colloidal quantum dot solar cells (CQDSCs), among other third-generation technologies, have recently experienced a level of success comparable to TOSCs. Finally, we compare the performance of TOSCs to CQDSCs, a complementary third-generation solar technology.