Center for Functional Nanomaterials Seminar

Colloidal quantum dots (CQDs) bridge the domains of crystalline inorganic and molecular semiconductors. These tiny nanocrystals synthesized in the solution phase can be coated on substrates using simple methods like drop-casting, spin-coating etc. and have demonstrated potential applications in large area, highly efficient low-cost photovoltaics. The quantum optical property of nanocrystals permits to tune the absorption properties, enabling to harvest the entire solar spectrum from visible to near-IR wavelengths. There has been rapid progress to achieve decent power conversion efficiency (PCE) using various types of CQDs. Mainly, two types of device architectures have been realized. Firstly, the Schottky device is realized in terms of a depletion region driving electron-hole pair separation on the semiconductor side of a junction between an opaque low-work-function metal and a p-type CQD film. Secondly, the depleted-heterojunction architecture employs a CQD layer on top of transparent conductive oxide (TCO) in which, exciton separation takes place at the heterointerface between the CQD film and the TCO. A decent PCE of over 5% have been achieved very recently. Bulk heterojunction architecture even pushes it further to 5.5%. Despite such rapid progress, understanding of carrier transport, surface passivation and other fundamental properties of nanocrystals as well as processing of CQD photovoltaics remains open in this research area. Additionally, further improvement of device performance and stability are other key issues and very challenging.