posted on 2019-09-30, 14:35authored byRafal Sliz, Marc Lejay, James Z. Fan, Min-Jae Choi, Sachin Kinge, Sjoerd Hoogland, Tapio Fabritius, F. Pelayo García de Arquer, Edward H. Sargent
Colloidal
quantum dots (CQDs) have recently gained attention as
materials for manufacturing optoelectronic devices in view of their
tunable light absorption and emission properties and compatibility
with low-temperature thin-film manufacture. The realization of CQD
inkjet-printed infrared photodetectors has thus far been hindered
by incompatibility between the chemical processes that produce state-of-the-art
CQD solution-exchanged inks and the requirements of ink formulations
for inkjet materials processing. To achieve inkjet-printed CQD solids
with a high degree of reproducibility, as well as with the needed
morphological and optoelectronic characteristics, we sought to overcome
the mismatch among these processing conditions. In this study, we
design CQD inks by simultaneous evaluation of requirements regarding
ink colloidal stability, jetting conditions, and film morphology for
different dots and solvents. The new inks remain colloidally stable,
achieved through a design that suppresses the reductant properties
of amines on the dots’ surface. After drop ejection from the
nozzle, the quantum dot material is immobilized on the substrate surface
due to the rapid evaporation of the low boiling point amine-based
compound. Concurrently, the high boiling point solvent allows for
the formation of a thin film of high uniformity, as is required for
the fabrication of high-performance IR photodetectors. We fabricate
inkjet-printed photodetectors exhibiting the highest specific detectivities
reported to date (above 1012 Jones across the IR) in an
inkjet-printed quantum dot film. As a patternable CMOS-compatible
process, the work offers routes to integrated sensing devices and
systems.