The Fall Semester Seminar
■ Topic : Directly-Printed Colloidal Quantum Dot Solar Cells
■ Speaker : Dr. Jin Young Kim (Fuel Cell Research Center, KIST)
■ Date & Time : December 8, 2015 (Tue), 16:00
■ Venue : KAIST Applied Engineering B/D(W1), Multimedia Lecture Hall (1st Floor)
■ Abstract :
In recent years there has been a growing interest in developing new approaches for the manufacture of photovoltaic devices in order to lower their cost while simultaneously improving their power conversion efficiency. Colloidal quantum dots (CQDs) offer a promising path towards high efficiency solution-processed photovoltaics. Significant progress in CQD solar cell device performance has been achieved and certified power conversion efficiencies as high as 10% have been reported. To date, CQD film processing has relied on a series of sequential deposition steps to achieve useful photon absorption and electronic transport. Serially processed CQD multi-layer film fabrication, each layer requiring its own ligand exchanging procedure, is time-intensive and wasteful in its materials utilization. Furthermore, such a film processing can inevitably induce distinct interfaces inside CQD film, which may act as barriers to electronic transport. In order to produce more versatile and economically viable CQD solar cells, it is important to simplify film preparation procedures and improve materials utilization. Here we present one-step fabrication strategies of CQD films by employing a stable CQD ink where each quantum dot is capped in thesolution phase with its final, electronically favorable ligand. Despite these potential advantages, such an approach for fabricating CQD films in photovoltaic applications has yet to be demonstrated. Recently, we developed a method to prepare a stable solution of CQDs with various types of short ligand molecules via a two-phase exchange to transfer long and bulky ligand capped CQDs to a short linker-capped system in a polar solvent. This strategy leads to direct printing of a CQD ‘ink’ to be integrated into CQD solar cells. The choice of surface passivant, and the control of its coverage over each individual CQD, enable manipulation of the electrical and optical properties of the final solid-state CQD film. In this talk, we will illustrate how these new approaches of CQD film fabrication yields high performance CQD photovoltaics and photodetectors.