Simultaneous Improvement of Charge Generation and Extraction in Colloidal Quantum Dot Photovoltaics Through Optical Management

Abstract

Inverted structure heterojunction colloidal quantum dot (CQD) photovoltaic devices with an improved performance are developed using single-step coated CQD active layers with a thickness of approximate to 60 nm. This improved performance is achieved by managing the device architecture to simultaneously enhance charge generation and extraction by raising optical absorption within the depletion region. The devices are composed of an ITO/PEDOT:PSS/PbS-CQD/ZnO/Al structure, in which the p-n heterojunction is placed at the rear (i.e., opposite to the side of illumination) of the devices (denoted as R-Cell). Sufficient optical generation is achieved at very low CQD layer thicknesses of 45-60 nm because of the constructive interference caused by the insertion of ZnO between the CQD and the Al electrode. The power conversion efficiency (PCE) of R-Cells containing a thin CQD layers (approximate to 60 nm) is much higher (approximate to 6%) than that of conventional devices containing CQD layers with a thickness of approximate to 300 nm (PCE approximate to 4.5%). This optical management strategy provides a general guide to obtain the optimal trade-off between generation and extraction in planar p-n junction solar cells. In terms of device engineering, all the layers in our R-Cells are fabricated using single coating, which can lead to compatibility with high-throughput processes.