Ligand-Free Synthesis of Aluminum-Doped Zinc Oxide Nanocrystals and their Use as Optical Spacers in Color-Tuned Highly Efficient Organic Solar Cells

• Published in: Advanced functional materials 2016, Vol.26 (2), p.243-253
• Main Authors: Gaceur, Meriem, Dkhil, Sadok Ben, Duché, David, Bencheikh, Fatima, Simon, Jean-Jacques, Escoubas, Ludovic, Mansour, Mahdi, Guerrero, Antonio, Garcia-Belmonte, Germà, Liu, Xianjie, Fahlman, Mats, Dachraoui, Walid, Diallo, Abdou Karim, Videlot-Ackermann, Christine, Margeat, Olivier, Ackermann, Jörg
• Format: Article
• Language: English
• Subjects: Azo; Chemical Sciences; Color; Engineering Sciences; interfacial layers; Material chemistry; Micro and nanotechnologies; Microelectronics; Nanocrystals; organic solar cells; Photovoltaic cells; Polymer blends; Solar cells; Spacers; Zinc oxide
• ISSN: 1616-301X; 1616-3028; 1616-3028
• DOI: 10.1002/adfm.201502929

The color of polymer solar cells using an opaque electrode is given by the reflected light, which depends on the composition and thickness of each layer of the device. Metal‐oxide‐based optical spacers are intensively studied in polymer solar cells aiming to optimize the light absorption. However, the low conductivity of materials such as ZnO and TiO2 limits the thickness of such optical spacers to tenths of nanometers. A novel synthesis route of cluster‐free Al‐doped ZnO (AZO) nanocrystals (NCs) is presented for solution processing of highly conductive layers without the need of temperature annealing, including thick optical spacers on top of polymer blends. The processing of 80 nm thick optical spacers based on AZO nanocrystal solutions on top of 200 nm thick polymer blend layer is demonstrated leading to improved photocurrent density of 17% compared to solar cells using standard active layers of 90 nm in combination with thin ZnO‐based optical spacers. These AZO NCs also open new opportunities for the processing of high‐efficiency color tuned solar cells. For the first time, it is shown that applying solution‐processed thick optical spacer with polymer blends of different thicknesses can process solar cells of similar efficiency over 7% but of different colors. A facile Al‐doped ZnO nanocrystal synthesis for solution‐processed electron extraction layer and playing as well as optical spacer in regular polymer solar cells is presented. A high power conversion efficiency together with fine‐tuning of the reflected cell color is obtained. Thick layers of this annealing‐free conductive film (up to 80 nm) together with thick layers of active blends (up to 200 nm) strongly improve the compatibility of polymer solar cells with large‐scale robust solution processing.