Air-stable n-type colloidal quantum dot solids

Abstract

Colloidal quantum dots (CQDs) offer promise in flexible electronics, light sensing and energy conversion. These applications rely on rectifying junctions that require the creation of high-quality CQD solids that are controllably n-type (electron-rich) or p-type (hole-rich). Unfortunately, n-type semiconductors made using soft matter are notoriously prone to oxidation within minutes of air exposure. Here we report high-performance, air-stable n-type CQD solids. Using density functional theory we identify inorganic passivants that bind strongly to the CQD surface and repel oxidative attack. A materials processing strategy that wards off strong protic attack by polar solvents enabled the synthesis of an air-stable n-type PbS CQD solid. This material was used to build an air-processed inverted quantum junction device, which shows the highest current density from any CQD solar cell and a solar power conversion efficiency as high as 8%. We also feature the n-type CQD solid in the rapid, sensitive, and specific detection of atmospheric NO2. This work paves the way for new families of electronic devices that leverage air-stable quantum-tuned materials.

Molecular Oxygen Induced in-Gap States in PbS Quantum Dots

“…To engineer IGS-free QDs for optoelectronic applications, we need to first reduce the surface oxygen during the postsynthesis treatment process and ideally also fully passivate the surface with ligands that can block the readsorption of O 2 on QDs. 10,11 …”

The role of surface passivation for efficient and photostable PbS quantum dot solar cells

“…The solution processability, quantum confinement and inorganic nature of colloidal quantum dots (QDs) have made them one of promising materials for low cost, high efficiency, third generation photovoltaic technology [1][2][3][4][5][6] . Since the first reports 1,2 , a dramatic improvement in power conversion efficiency (PCE) has been achieved overpassing 9% with PbS(Se) QDs leading the race as the material of choice 5 .…”

“…Since the first reports 1,2 , a dramatic improvement in power conversion efficiency (PCE) has been achieved overpassing 9% with PbS(Se) QDs leading the race as the material of choice 5 . This progress has been underpinned by the design of new heterostructures [5][6][7][8] , improved surface passivation schemes 3,4 and advanced device architectures for more efficient charge collection and suppressed recombination 9,10 . While improvement in PCE of QD solar cells has been thoroughly sought after over the years, the photostability of this technology still remains an open challenge to further increase its technology readiness level, albeit initial promising results on low-performance PbS QD solar cells 11 .…”

Inorganic-ligand exchanging time effect in PbS quantum dot solar cell

“…Therefore, control of the ligand exchange process which efficiently substitutes the surface from long ligands to short molecules is necessary for CQD-based device applications. 10,11 Enhanced performances of CQD solar cells using the inorganic halide ligands (e.g., Cl À , Br À , I À ) have been recently reported, 12,13 but the detailed characterization of the CQD film during the ligand exchange process has not been well investigated. Those parameters such as packing density or halide ion density on the surface should be considered for an effective way to control the surface status and further improve photovoltaic performance.…”