Colloidal Quantum Dot Tandem Photovoltaics Employing a Novel Hole-blocking Injection Layer Concept

Colloidal quantum dot (CQD) tandem photovoltaics (PV) are of interest as candidates for next-generation PV due to their potential for low-cost fabrication and compatibility with lightweight flexible packaging. In this work, we present a CQD tandem PV device that employs indium tin oxide (ITO) as interconnection layer and a novel injection layer with hole-blocking functionality. A lead sulfide (PbS) CQD heterojunction is formed with C60 in each subcell, yet the traditional BPhen/Ag contact is replaced with ITO. We demonstrate that a hole-blocking injection layer must be inserted between C60 and interconnection layer ITO in order to achieve excellent electrical contact between the two. We obtain a doubling in open-circuit voltage and maintain the high fill factor of the single-junction device. This device structure is particularly suited to multiple-cell tandem PV.