Open-cage fullerenes as n-type materials in organic photovoltaics: Relevance of frontier energy levels, carrier mobility and morphology of different sizable open-cage fullerenes with power conversion efficiency in devices

Abstract

Organic bulk heterojunction (OBHJ) photovoltaics, incorporating open-cage fullerenes with orifice-size of 8, 12, 13, 16 and 20-membered-rings as n-type materials, display power conversion efficiency (PCE) up to 2.9% by the 8-membered-ring fullerene under AM 1.5G irradiation; their PCEs decrease as the orifice-size of open-cage fullerene increases, primarily due to electron-mobility descends as the cage is ruptured to larger holes.