Colloidal quantum dots (CQDs) are freestanding, confinement-based energy-band-tunable materials that enable the formation of thin-film device structures for various optoelectronic applications. Group III−V CQDs (InP, InAs, and InSb) without toxic elements such as Cd, Pb, and Hg are currently being extensively explored, as the covalent crystal nature in bonding can provide robustness toward external stresses. Despite successful implementation in specific areas, such as CQD-based light downconversion optoelectronics, most state-of-the-art group III−V CQD-based devices still suffer from low efficiency compared to other CQD-based devices. In this Focus Review, we address the challenges specific to efficient group III−V CQD-based optoelectronics design and fabrication and highlight recent approaches for overcoming these challenges, in view of synthesis, surface modification, and effective carrier modulation. Finally, we discuss the perspectives and outlook for achieving efficient group III−V CQD optoelectronics.

The past decade has seen a dramatic surge in the power conversion efficiency (PCE) of next‐generation solution‐processed thin‐film solar cells rapidly closing the gap in PCE of commercially‐available photovoltaic (PV) cells. Yet the operational stability of such new PVs leaves a lot to be desired. Specifically, chemical reaction with absorbers via high‐energy photons transmitted through the typically‐adapted metal oxide electron transporting layers (ETLs), and photocatalytic degradation at interfaces are considered detrimental to the device performance. Herein, the authors introduce a device architecture using the narrow‐gap, Indium Arsenide colloidal quantum dots (CQDs) with discrete electronic states as an ETL in high‐efficiency solution‐processed PVs. High‐performing PM6:Y6 organic PVs (OPVs) achieve a PCE of 15.1%. More importantly, as the operating stability of the device is significantly improved, retaining above 80% of the original PCE over 1000 min under continuous illumination, a Newport‐certified PCE of 13.1% is reported for nonencapsulated OPVs measured under ambient air. Based on operando studies as well as optical simulations, it suggested that the InAs CQD ETLs with discrete energy states effectively cut‐off high‐energy photons while selectively collecting electrons from the absorber. The findings of this works enable high‐efficiency solution‐processed PVs with enhanced durability under operating conditions.

performance has gradually improved reaching a photoconversion efficiency of over 18%, [6] photo-active materials typically contain the toxic element Pb as in PbS or CsPbI 3 CQDs. [6][7][8][9][10] There have been endeavors to find suitable candidates having a band gap for efficient solar photoconversion replacing the current Pb-containing materials. [11][12][13][14][15][16] Based on the high absorptivity in the solar spectral range and high dielectric constant, AgBiS 2 CQD materials show great potential for nextgeneration thin-film photovoltaics. [11,[17][18] So far, the solar cells using AgBiS 2 CQDs present the highest power conversion efficiency (PCE) of 9.2%, while the PCEs using other lead-free CQD materials are still less than 5%. [19] Nevertheless, there is still room for further improvement in terms of efficiency and stability which will make it competitive.In particular, the conventional AgBiS 2 CQD solar cells have a problem in that their charge extraction is poor despite their excellent light absorption. For example, the carrier transport problem becomes more severe in a higher charge carrier density under light illumination. [11,20] Typical deviations from the ideal current density result from the low mobility of carriers or charge imbalance in the structure due to interfacial recombination. [21,22] Until recently, most efforts have focused on improving the structural or size homogeneity of AgBiS 2 CQDs during their synthesis, [19,23] or controlling the surface trapping of the synthesized CQDs by developing surface modification processes. [20,24] The increase in material property has led to an increase in the PCE to some extent, but the problem of recombination at the interface has not been investigated so far.Here, we introduce a hybrid mixture of a charge acceptor and donor at the interface to promote carrier extraction in AgBiS 2 CQD solar cells. [25][26][27] Specifically, we use a quantum dot polymer bulk heterojunction (QPB) film composed of a blend of AgBiS 2 CQD and PTB7 (Poly [[4,8-bis[(2-ethylhexyl)oxy] benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophenediyl]]) polymers at the hole collecting interface and present an efficient, robust AgBiS 2 CQD solar cells. The PCE of the QPB-AgBiS 2 solar cell is increased by up to 6.78% compared to cells without QPB Remarkable progress over the past decade in photovoltaics using solutionprocessed nanomaterials as light absorbers has placed colloidal quantum dot (CQD)-based devices on the map. As such, AgBiS 2 CQDs have garnered significant attention as materials exhibiting a high absorptivity with environmentally benign alternatives to Pb-chalcogenide or Pb halide perovskite-CQDs. Yet, AgBiS 2 CQD-based solar cells have gravely underperformed compared to Pb-containing devices, particularly in the metrics of charge carrier extraction from the AgBiS 2 absorber, hence its relative mediocrity. To specifically address the extraction efficiency, a bulk heterostructure (QPB) interlayer at the CQD/polymer interface i...

The tunable band edge position of colloidal quantum dot (CQD) films is a key part of efficient optoelectronic device design of various forms such as photovoltaics, light-emitting diodes, and photodetectors. An accurate estimation of shifts in the band edge position of CQD layers is still considered challenging, especially when the CQD films are nonconductive. Here, we investigate the effect of nonconductive CQD films on photoelectron spectroscopy (PES) and photoelectron yield spectroscopy (PYS). We demonstrate control of systematic band edge positions by fractional ligand replacement of nonconductive CQD film characterized with photoelectron yield spectroscopy and density functional theory calculations. As-synthesized CQDs with insulating oleate ligands were fractionally replaced with trans-3,5-difluorocinnamic acid molecules in a nonpolar solution. The fractionally replaced surface-bound ligands are quantitatively analyzed using 1H and 19F nuclear magnetic resonance (NMR) spectroscopy. We found that the energy levels of nonconducting CQD films shift linearly as a function of the number of bound trans-3,5-difluorocinnamates with specific dipole moments while retaining hydrophobic wettability.

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