Influence of the Post-Synthesis Annealing on Device Performance of PbS Quantum Dot Photoconductive Detectors

Abstract

Colloidal quantum dots (CQDs) are attractive materials for optoelectronic devices due to their low‐cost, facile processing and size‐dependent band‐gap tunability and quantum confinement effect. In particular, narrow band‐gap lead chalcogenide CQDs have been widely used in near infrared optoelectronics. Here, in this paper, the influence of post‐synthesis annealing treatment on the active layer of PbS CQDs in photoconductive detector Au/PbS(110 nm)/Au is investigated by increasing the annealing temperatures from 80 to 140 °C, and the maximum photo‐to‐dark current ratio K and the specific detectivity D* are enhanced up to 9.7 and 23.2 times than those of the as‐made device, respectively, after the PbS active layer is annealed at 120 °C. Experimental data show that the dramatic enhancement of the device performance is due to the mobility enhancement of charge carriers and the perfect morphology of the PbS film after its annealing. Further, the underneath mechanisms for the enhanced‐performance after annealing are discussed in details, showing the performance of “top‐film” device is higher than that of the “bottom‐film” device.

Annealing-Temperature Dependent Carrier-Transportation in ZnO/PbS Quantum Dot Solar Cells Fabricated Using Liquid-Phase Ligand Exchange Methods

“…This was chiefly due to increasing QD coupling, caused by a necking phenomenon, as confirmed by the broadening of the exciton band (Figure 2a). Similar annealing temperature dependency has been reported for PbS QD films prepared using a solid-phase ligand exchange method [29,30]. However, the temperature at which the absorption band began widening was lower in the liquid-phase ligand exchange films.…”

“…The energy level alignment of the QD layers using different ligand treatments was demonstrated as being useful for elongating carrier diffusion lengths, thereby increasing short circuit current density [27]. In addition, post-annealing CQD layers have been reported to help enhance PCE [28][29][30].…”

Precise Control of the Oxidation State of PbS Quantum Dots Using Rapid Thermal Annealing for Infrared Photodetectors

“…The effects of annealing on QD devices using a furnace or hot plate have been well investigated because QDs have been studied for device applications. The representative effect of thermal annealing is the enhancement of carrier transport in QD devices . Conventional annealing methods using furnaces have some drawbacks from the long annealing times, an inevitable result owing to their slow ramp-up rate.…”

“…Furthermore, it is significant to note that the RTA process can anneal the QD films at higher temperatures than the conventional annealing process. Annealing in air for long periods may increase gain but decrease the frequency response, and, therefore, a high D * is difficult to achieve at high frequencies. It is well-known that there is a fundamental trade-off between R and BW in PbS QD-based photoconductors. , When the gain is high due to prolonged carrier lifetime, the frequency response is low for the same reason.…”

“…The representative effect of thermal annealing is the enhancement of carrier transport in QD devices. 14 Conventional annealing methods using furnaces have some drawbacks from the long annealing times, an inevitable result owing to their slow ramp-up rate. These relatively long annealing periods induce diffusion processes such as necking or fusing of nanocrystals, which results in a weakening of the quantum confinement.…”