Microscopic investigation into higher efficiency and stability of inverted organic solar cells compared to conventional cells

Abstract

Abstract The performance of organic solar cells has remarkably improved recently, where the cell structures are important for achieving high efficiency and stability. The formation and accumulation of long-lived charges in the cells are critical for the efficiency and stability of the cells; however, their relations with the cell structures have not yet been clarified from a microscopic viewpoint. Here, we report the microscopic investigation into higher efficiency and stability of inverted organic solar cells compared to those of conventional cells, even though the same photoactive layers are utilized. We have directly observed the formation and accumulation of long-lived charges in these cells with electron spin resonance (ESR) at a molecular level. We have found the reduced effects of formation and accumulation of long-lived charges in the inverted cells for the efficiency and stability compared to the case of the conventional cells. These findings provide striking advance in fundamental understanding, which are useful for further clarifying the operation mechanism of organic solar cells as well as further improving their efficiency and stability.