Quantum-Size-Effect Tuning Enables Narrowband IR Photodetection with Low Sunlight Interference

Abstract

Infrared photodetection enables depth imaging techniques such as structured light and time-of-flight. Traditional photodetectors rely on silicon (Si); however, the bandgap of Si limits photodetection to wavelengths shorter than 1100 nm. Photodetector operation centered at 1370 nm benefits from lower sunlight interference due to atmospheric absorption. Here, we report 1370 nm-operating colloidal quantum dot (CQD) photodetectors and evaluate their outdoor performance. We develop a surface-ligand engineering strategy to tune the electronic properties of each CQD layer and fabricate photodetectors in an inverted (PIN) architecture. The strategy enables photodetectors with an external quantum efficiency of 75% and a low dark current (1 μA/cm 2 ). Outdoor testing demonstrates that CQD-based photodetectors combined with a 10 nm-line width bandpass filter centered at 1370 nm achieve over 2 orders of magnitude (140× at incident intensity 1 μW/cm 2 ) higher signal-to-background ratio than do Si-based photodetectors that use an analogous bandpass filter centered at 905 nm.

Control over Charge Carrier Mobility in the Hole Transport Layer Enables Fast Colloidal Quantum Dot Infrared Photodetectors

“…19−22 Solution processed (sol−gel) NiOx HTL has been used with PbS CQD active layers in the past to achieve an EQE of 24% at 1 V reverse bias. 23 The reported valence band position of the sol− gel NiOx (5.4 eV) is deep and close to the valence band energy reported for the PbS CQD based absorber layer (5.2−5.5 eV 2,3 ). This band alignment mismatch obstructs efficient charge extraction, leading to low EQE values.…”

“…To investigate the temporal response of PbS CQD photodetectors, we fabricated p-i-n devices operating at 1370 nm based on prior approaches. 2,3 The structure of this device is shown in Figure 1a PbS CQDs were utilized in this work, one having an excitonic peak at 1350 nm and the other at 930 nm. Smaller CQDs were used for HTL and HBL deposition, while larger dots were used for the absorber layer.…”

“…For the absorber layer (bandgap ∼0.9 eV), a mixed halide exchange is used. 2 For the HBL, PbS CQDs (1.3 eV bandgap) exchanged with trans-4-(trifluoromethyl) cinnamic acid (TFCA) ligands are chosen, since these provide n-type behavior and increase the work function of the HBL, facilitating electron transport to the electrode. 3 The devices exhibit 50% EQE, 3 × 10 −3 mA cm −2 dark current at 1 V reverse bias, and ∼10 3 rectification ratio (Figure S1).…”

Electron‐Transport Layers Employing Strongly Bound Ligands Enhance Stability in Colloidal Quantum Dot Infrared Photodetectors

“…To fabricate the CQD ETLs, we select two different n-type ligands, TBAI as a representative inorganic atomic ligand, and TFCA as an organic ligand (see Figure 1a for their chemical structures). We used TBAI-known to result in n-type behavior of CQD solids and increase their conductivity, [14][15][16] and recently used in photodetectors [17] -as control; these provided a basis of comparison with the new class of ETLs developed herein based on the organic carboxylate TFCA. Both classes of ligand contain halide: in the case of TBAI, the iodine atoms attach directly to the CQD surface; while the fluorine atoms in TFCA do not (Figure 1c).…”

Organic and quantum dot hybrid photodetectors: towards full-band and fast detection

“…Sargent's group has contributed a lot to developing short-wave infrared QPDs with high response speed. 49,50,52 They put forward a resurfacing strategy for developing the enhanced coupling QDs with high hole mobility, which can enable a superior EQE of B70% and a specific detectivity over 10 12 Jones at 1550 nm with a response time of 7 ns. 50 Such fast response speed may be attributed to the low exciton binding energy, high carrier mobility and favorable device structure, which can enable fast exciton dissociation, carrier transport and extraction for photodetectors even without bias.…”