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

• Published in: Advanced functional materials 2015-10, Vol.25 (39), p.6241-6249
• Main Authors: Aqoma, Havid, Barange, Nilesh, Ryu, Ilhwan, Yim, Sanggyu, Do, Young Rag, Cho, Shinuk, Ko, Doo-Hyun, Jang, Sung-Yeon
• Format: Article
• Language: English
• Subjects: Charge; charge extraction; Coating; colloidal quantum dots; Devices; Extraction; heterojunctions; Management; optical enhancement; Photovoltaic cells; photovoltaic devices; Qunatum dots; Solar cells; Thin films
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201502664

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 ≈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 (≈60 nm) is much higher (≈6%) than that of conventional devices containing CQD layers with a thickness of ≈300 nm (PCE ≈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. Rear‐junction colloidal quantum dot (CQD) photovoltaic devices with an improved performance are developed using single‐step coated thin CQD active layers (thickness of ≈60 nm). Charge generation and extraction in CQD photovoltaic devices are simultaneously improved through optical management of thin CQD active layers. Sufficient optical generation and efficient charge extraction afford a power conversion efficiency of ≈6%.