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Strong optical absorption by a semiconductor is a highly desirable property for many optoelectronic and photovoltaic applications. The optimal thickness of a semiconductor absorber is primarily determined by its absorption coefficient. To date, this parameter has been considered as a fundamental material property, and efforts to realize thinner photovoltaics have relied on light-trapping structures that add complexity and cost. Here we demonstrate that engineering cation disorder in a ternary chalcogenide semiconductor leads to considerable absorption increase due to enhancement of the optical transition matrix elements. We show that cation-disorder-engineered AgBiS2 colloidal nanocrystals offer an absorption coefficient that is higher than other photovoltaic materials, enabling highly efficient extremely thin absorber photovoltaic devices. We report solution-processed, environmentally friendly, 30-nm-thick solar cells with short-circuit current density of 27 mA cm−2, a power conversion efficiency of 9.17% (8.85% certified) and high stability under ambient conditions.

Low-cost, nontoxic, and earth-abundant photovoltaic materials are long-sought targets in the solar cell research community. Perovskite-inspired materials have emerged as promising candidates for this goal, with researchers employing materials design strategies including structural, dimensional, and compositional transformations to avoid the use of rare and toxic elemental constituents, while attempting to maintain high optoelectronic performance. These strategies have recently been invoked to propose Ti-based vacancy-ordered halide perovskites (A

Solution processed semiconductor lasers have achieved much success across the nanomaterial research community, including in organic semiconductors1,2, perovskites3,4 and colloidal semiconductor nanocrystals5,6. The ease of integration with other photonic components, and the potential for upscaling using emerging large area fabrication technologies, such as roll-to-roll7, make these lasers attractive as low-cost photonic light sources that can find use in a variety of applications: integrated photonic circuitry8,9, telecommunications10,11, chemo-/bio-sensing12,13, security14, and lab-on-chip experiments15. However, for fiber-optic or free-space optical (FPO) communications and eye-safe LIDAR applications, room temperature solution-processed lasers have remained elusive. Here we report the first solution processed laser, comprising PbS colloidal quantum dots (CQDs) integrated on a distributed feedback (DFB) cavitiy, with tuneable lasing wavelength from 1.55 μm - 1.65 μm. These lasers operate at room temperature and exhibit linewidths as low as ~0.9 meV.

Low-cost, non-toxic and earth-abundant photovoltaic materials are a long-sought target in the solar cell research community. Perovskite-inspired materials have emerged as promising candidates for this goal, with researchers employing materials design strategies including structural, dimensional and compositional transformations to avoid the use of rare and toxic elemental constituents, while attempting to maintain high optoelectronic performance. These strategies have recently been invoked to propose Ti-based vacancy-ordered halide perovskites (A₂TiX₆; A = CH₃NH₃, Cs, Rb, K; X = I, Br, Cl) for photovoltaic operation, following the initial promise of Cs₂SnX₆ compounds. Theoretical investigations of these materials, however, consistently overestimate their band gaps – a fundamental property for photovoltaic applications. Here, we reveal strong excitonic effects as the origin of this discrepancy between theory and experiment; a consequence of both low structural dimensionality and band localization. These findings have vital implications for the optoelectronic application of these compounds, while also highlighting the importance of frontier-orbital character for chemical substitution in materials design strategies.

Metal selenide nanocrystals have attracted attention as promising materials in photovoltaics and thermoelectrics. However, the expensive and labor-intensive synthesis methods utilized for the produ...

Low cost, multinary colloidal quantum dots (QDs) based on environmentally friendly elements, with bright, narrow-width, tunable near-infrared (NIR) luminescence are promising alternatives to Cd and Pb chalcogenide QDs for in vivo bio-imaging, LED and sensing applications. Herein, we demonstrate Pb/Cd free solution-processed colloidal luminescent Ag2ZnSnS4–ZnS (AZTS–ZnS) core–shell QDs with precise control over the ZnS shell thickness and thereby its optical properties. Unlike indium based multinary (I–III–VI group) core–shell QDs these nanocrystals show a narrow photoluminescence (PL) full width at half maximum (fwhm) of 105–110 meV in the first NIR window. By monitoring the starting AZTS core size, we achieve tunable emission over a small NIR window in these QDs with the best PL quantum yield (PLQY) of 17.4%., Passivation and optimization of luminescent AZTS QDs with ZnS shells gave rise to a ∼30-fold increase in the PLQY results in RoHS compliant low-cost, bright and tunable NIR-luminescent phosphors for bio-imaging and LED applications.

Two major challenges exist before colloidal nanocrystal solar cells can take their place in the market: So far, these devices are based on Pb/Cd-containing nanocrystals, and second, the synthesis of these nanocrystals takes place in an inert atmosphere at elevated temperatures due to the use of air-sensitive chemicals. In this report, a room-temperature, ambient-air synthesis for nontoxic AgBiS2 nanocrystals is presented. As this method utilizes stable precursors, the need for the use of a protective environment is eliminated, enabling the large-scale production of AgBiS2 nanocrystals. The production cost of AgBiS2 NCs at room temperature and under ambient conditions reduces by ∼60% compared to prior reports based on hot injection, and the solar cells made of these nanocrystals yield a promising power conversion efficiency (PCE) of 5.5%, the highest reported to date for a colloidal nanocrystal material free of Pb or Cd synthesized at room temperature and under ambient conditions.

Heavy-metal-free colloidal nanocrystals are gaining due attention as low-cost, semiconducting materials for solution-processed optoelectronic applications. One common limitation of such materials is their limited carrier transport and trap-assisted recombination, which impede the performance of thick photoactive layers. Here we mix small-size and large-size AgBiS

The use of colloidal quantum dots (CQDs) as a gain medium in infrared laser devices has been underpinned by the need for high pumping intensities, very short gain lifetimes, and low gain coefficients. Here, PbS/PbSSe core/alloyed-shell CQDs are employed as an infrared gain medium that results in highly suppressed Auger recombination with a lifetime of 485 ps, lowering the amplified spontaneous emission (ASE) threshold down to 300 µJ cm

Cesium titanium halide perovskites are novel lead-free optoelectronic materials that have attracted attention in the last two years for their application in solar cells with power conversion efficiencies reaching 3.3%. We report here the first colloidal synthesis of pure and mixed bromide–iodide cesium titanium perovskite nanocrystals with a bandgap tunable from 2.3 eV to 1.2 eV.

Broadband infrared photodetectors have profound importance in diverse applications including security, gas sensing, bioimaging, spectroscopy for food quality, and recycling, just to name a few. Yet, these applications can currently be served by expensive epitaxially grown photodetectors, limiting their market potential and social impact. The use of colloidal quantum dots (CQDs) and 2D materials in a hybrid layout is an attractive alternative to design low-cost complementary metal-oxide-semiconductor (CMOS) compatible infrared photodetectors. However, the spectral sensitivity of these conventional hybrid detectors is restricted to 2.1 µm. Herein, a hybrid structure comprising molybdenum disulfide (MoS2) with lead selenide (PbSe) CQDs is presented to extend their sensitivity further toward the mid-wave infrared, up to 3 µm. A room-temperature responsivity of 137.6 A/W and a detectivity of 7.7 × 10^10 Jones are achieved at 2.55 µm owing to highly efficient photoexcited carrier separation at the interface of MoS2 and PbSe in combination with an oxide coating to reduce dark current; the highest value is yet for a PbSe-based hybrid device. These findings strongly support the successful fabrication of hybrid devices, which may pave the pathway for cost-effective, high-performance, next-generation, novel photodetectors. The authors acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research (grant agreement no. 725165) as well as Graphene Flagship under Grant Agreement Nr. 881603 (Core3). The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO), and the “Fondo Europeo de Desarrollo Regional” (FEDER) through grant TEC2017-88655-R, from the Spanish State Research Agency through the “Severo Ochoa” program for Centers of Excellence in R&D (CEX2019-000910-S), from Fundació Cellex, Fundació Mir-Puig, and from Generalitat de Catalunya through the CERCA program.

Kesterite, or Cu2ZnSn(S,Se)4 (CZTS) is promising in developing sustainable PV technology due to its earth-abundant, non-toxic composition. However, issues including instability of interface, high density of defects that fails to allow the short charge-collection length to meet its light absorption needs, use of Cd that fails to comply with the restriction of hazardous substances (RoSH), are promoting the development of alternative, eco-friendly device structure. Here, this study reports an important progress on this subject by adopting the superstrate configuration to kesterite, thus to realize advantageous light management and high defect tolerance in an ultrathin device. By incorporating Ag in kesterite to overcome the detrimental alignment at the pristine interface, a solar cell with PCE of 8.1% has been fabricated with ~ 200 nm absorber and ~ 15 nm TiO2 buffer, representing a PCE improvement of nearly three-fold from the baseline Cu2ZnSn(S,Se)4 device and breaking the 5% PCE limit for superstrate kesterite cells to date. Moreover, this enables the sole use of TiO2 as novel buffer material free of toxic Cd. Further analysis reveals the critical role of Ag in synergistically tailoring band offset and bandgap, along with largely reduced density of defects, leading to this substantial performance improvement.

Solid-state broadband light emitters in the visible have revolutionized today's lighting technology achieving compact footprints, flexible form factors, long lifetimes, and high energy saving, although their counterparts in the infrared are still in the development phase. To date, broadband emitters in the infrared have relied on phosphor-downconverted light emitters based on atomic optical transitions in transition metal or rare earth elements in the phosphor layer resulting in limited spectral bandwidths in the near-infrared and preventing their integration into electrically driven light-emitting diodes (LEDs). Herein, phosphor-converted LEDs based on engineered stacks of multi-bandgap colloidal quantum dots (CQDs) are reported as a novel class of broadband emitters covering a broad short-wave infrared (SWIR) spectrum from 1050–1650 nm with a full-width-half-maximum of 400 nm, delivering 14 mW of optical power with a quantum efficiency of 5.4% and power conversion efficiency of 13%. Leveraging the electrical conductivity of the CQD stacks, further, the first broadband SWIR-active LED is demonstrated, paving the way toward complementary metal–oxide–semiconductor integrated broadband emitters for on-chip spectrometers and low-cost volume manufacturing. SWIR spectroscopy is employed to illustrate the practical relevance of the emitters in food and material identification case studies.

Recent approaches to develop infrared photodetectors characterized by high sensitivities, broadband spectral coverage, easy integration with silicon electronics and low cost have been based on hybrid structures of transition metal dichalcogenides (TMDCs) and PbS colloidal quantum dots (CQDs). However, to date, such photodetectors have been reported with high sensitivity up to 1.5 $\mu$m. Here we extend the spectral coverage of this technology towards 2 $\mu$m demonstrating for the first time compelling performance with responsivities 1400 A/W at 1.8 $\mu$m with 1V bias and detectivities as high as $10^{12}$ Jones at room temperature. To do this we studied two TMDC materials as a carrier transport layer, tungsten disulfide (WS$_2$) and molybdenum disulfide (MoS$_2$) and demonstrate that WS$_2$ based hybrid photodetectors outperform those of MoS$_2$ due to a more adequate band alignment that favors carrier transfer from the CQDs., Comment: 24 pages including Supporting Information

Optical sensing in the mid- and long-wave infrared (MWIR, LWIR) is of paramount importance for a large spectrum of applications including environmental monitoring, gas sensing, hazard detection, food and product manufacturing inspection, and so forth. Yet, such applications to date are served by costly and complex epitaxially grown HgCdTe quantum-well and quantum-dot infrared photodetectors. The possibility of exploiting low-energy intraband transitions make colloidal quantum dots (CQD) an attractive low-cost alternative to expensive low bandgap materials for infrared applications. Unfortunately, fabrication of quantum dots exhibiting intraband absorption is technologically constrained by the requirement of controlled heavy doping, which has limited, so far, MWIR and LWIR CQD detectors to mercury-based materials. Here, we demonstrate intraband absorption and photodetection in heavily doped PbS colloidal quantum dots in the 5-9 µm range, beyond the PbS bulk band gap, with responsivities on the order of 10-4 A/W at 80 K. We have further developed a model based on quantum transport equations to understand the impact of electron population of the conduction band in the performance of intraband photodetectors and offer guidelines toward further performance improvement. I.R. acknowledges support from the Ministerio de Economiá , Industria y Competitividad of Spain via a Juan de la Cierva fellowship. The authors acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the “Fondo Europeo de Desarrollo Regional” (FEDER) through Grant TEC2017- 88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA and from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0522). S.C. acknowledge support from a Marie Curie Standard European Fellowship (“NAROBAND”, H2020-MSCA-IF-2016-750600).

Steady-state access to intraband transitions in colloidal quantum dots (CQDs), via heavy doping, allows exploiting the electromagnetic spectrum at energies below the band gap. CQD intraband optoelectronics opens up a new path to cheap mid- and long-wavelength infrared photodetectors and light-emitting devices, which today employ mostly epitaxial materials. As a recent field of experimental research, thorough studies of the basic properties of intraband transitions in CQDs are still lacking. In this work, we investigate the size and temperature dependence of the intraband transition in heavily n-doped PbS quantum dot (QD) films. We measure the absorption coefficient of the intraband transition to be in the order of $10^4$ cm$^{-1}$, which is comparable to the value of the interband absorption coefficient. Additionally, we determine the size-dependence of the oscillator strength of the intraband transition. We demonstrate a negative dependence of the intraband energy with temperature, in contrast to the positive dependence of the interband transition. We thank Dr. Iacopo Torre for helpful discussions. The authors acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the “Fondo Europeo de Desarrollo Regional” (FEDER) through grant TEC2017-88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA and from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Program for Centres of Excellence

By combining X-ray absorption fine structure and X-ray diffraction measurements with density functional and molecular dynamics simulations, we study the structure of a set of AgxBi1&minus, xS2 nanoparticles, a materials system of considerable current interest for photovoltaics. An apparent contradiction between the evidence provided by X-ray absorption and diffraction measurements is solved by means of the simulations. We find that disorder in the cation sublattice induces strong local distortions, leading to the appearance of short Ag&ndash, S bonds, the overall lattice symmetry remaining close to hexagonal.

The demonstration of the quantum confinement effect in colloidal quantum dots (QDs) has been extensively studied and exploited mainly in Pb and Cd chalcogenide systems. There has been an urgent need recently for the development of non(less)-toxic colloidal QDs to warrant compliance with current safety regulations (Restriction of Hazardous Substances (RoHS) Directive 2002/95/ EC). Herein, we report Pb/Cd-free, solution processed luminescent Ag2ZnSnS4 (AZTS) colloidal QDs. We present a selective and controlled amine and thiol-free synthesis of air stable luminescent AZTS QDs by the hot injection technique. By controlling the reaction conditions we obtain controlled size variation and demonstrate the quantum confinement effect that is in good agreement with the theoretically calculated values. The band gap of the AZTS QDs is size-tunable in the near-infrared from 740 to 850 nm. Finally, we passivate the surface with Zn-oleate, which yields higher quantum yield (QY), longer lifetime, and better colloidal stability

AgBiS2 nanocrystals have recently emerged as a RoHS compliant material for photovoltaics. This heavy-metal-free ternary chalcogenide can be prepared from earth-abundant precursors, is solution-processable and presents a high absorption coefficient as well as a suitable bandgap for solar cell applications. However, the full potential of AgBiS2 nanocrystals is yet to be realised; the highest efficiencies reported so far used very thin (~35 nm) absorbing layers due to the limited carrier transport and trap-assisted recombination that hinder the performance of thicker layers. In this work we implement a synthetic route to obtain larger size colloidal AgBiS2 nanocrystals, which in turn allows to fabricate thin film solar cells with higher mobility and reduced trap-assisted recombination, resulting in a power conversion efficiency of 6.4%, due to a photocurrent increase of 4 mA/cm2 compared to prior reports. We conclude by discussing on the main current challenges underpinning the photovoltaic performance of this material as well as strategies to further reduce the voltage and photocurrent losses.

PbS nanocrystals are an important narrow-gap material for solar cells and photodetectors. Nevertheless, their application may be limited because device performance can be affected by atmospheric conditions. Indeed, the presence of oxygen and/or water can degrade the active layers, possibly leading to device failure. Strategies to address this issue are therefore actively explored. Here we report a solution-processed PbS quantum dot solar cell, consisting of a PbS-silane functionalized reduced graphene oxide (PbS-rGO) layer on top of the PbS absorber film, which enhances device stability, especially when the solar cells are exposed to moisture. Power conversion efficiency (PCE) measurements demonstrate a slower degradation under continuous illumination for solar cells with PbS-rGO. When storing the samples under saturated water vapor, differences are even more remarkable: with PbS-rGO the solar cells essentially maintain their initial PCE, while the PCE of the PbS reference devices is reduced by 50% after 5 days. Scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy reveal the damage to the PbS films and the formation of PbSOx crystals in the PbS reference devices. Such crystals are not observed in the PbS-rGO devices, further supporting the importance of the PbS-rGO barrier layer.

The use of photothermal sensitizers to facilitate the sintering of polymer powders is rapidly becoming a pivotal additive manufacturing technology, impacting multiple sectors of industry. However, conventional carbon-based sensitizers can only produce black or gray objects. To create white or colorful prints with this method, visibly transparent equivalents are needed. Here, we address this problem by designing resonant photothermal sensitizers made of plasmonic nanoparticles that strongly absorb in the near-infrared, while only minimally interacting with visible light. Gold nanorods were coated with silica before being mixed with polyamide powders to create stable colorful nanocomposite powders. At resonance, these composites showed greatly improved light-to-heat conversion compared with equivalent composites using the industry standard carbon black as a sensitizer and could be sintered using low-power light sources. Furthermore, they appear much whiter and can produce brightly colored 3D objects when mixed with dyes. Our results open a new route to utilize plasmonic nanoparticles to produce colorful and functional 3D-printed objects.

Mobility engineering is one of the most important challenges that determine the optoelectronic performance of two-dimensional (2D) materials. So far, charged-impurity scattering and electrical-contact barriers have been suppressed through high-κ dielectrics and seamless contact engineering, giving rise to carrier-mobility improvement in exfoliated 2D semiconducting MoS2. Here we demonstrate a facile and scalable technique to effectively suppress both Coulomb scattering and electron–phonon scattering via the HfO2 overlayer, resulting in a large mobility improvement in CVD-grown monolayer MoS2, in excess of 60 cm2 V−1 s−1. Surface passivation and suppression of Coulomb scattering can partially contribute to the mobility increase. Interestingly, we correlate the mobility increase with phonon quenching through Raman and temperature-dependent mobility measurements. The experimental method is facile, industrially scalable, and renders phonon engineering an additional leverage towards further improvements in 2D semiconductor mobility and device performance.

Pb-chalcogenide colloidal quantum dots (CQDs) are attractive materials to be used as tuneable laser media across the infrared spectrum. However, excessive nonradiative Auger recombination due to the presence of trap states outcompetes light amplification by rapidly annihilating the exciton population, leading to high gain thresholds. Here, a binary blend is employed of CQDs and ZnO nanocrystals in order to passivate the in-gap trap states of PbS-CQD gain medium. Using transient absorption, a fivefold increase is measured in Auger lifetime demonstrating the suppression of trap-assisted Auger recombination. By doing so, a twofold reduction is achieved in amplified spontaneous emission (ASE) threshold. Finally, by integrating the proposed binary blend to a distributed feedback (DFB) resonator, single-mode lasing emission is demonstrated at 1650 nm with a linewidth of 1.23 nm (0.62 meV), operating at a low lasing threshold of ≈385 μJ cm-2 . The Auger suppression in this system has allowed to achieve unprecedented lasing emission stability for a CQD laser with recorded continuous operation of 5 h at room temperature and ambient conditions.

Metal halide perovskite nanocrystals (NCs) possess high photoluminescence (PL) quantum yield (PL) and color tunability. Yet, until now, it has been difficult to maintain the high PL observed in solution in spin-coated films. Here, we report a novel CsPbBr3 NCs room-temperature synthesis based on Cs acetate, which displays near-unity PL in solid-state films upon post-synthetic treatment with lead bromide. The as-synthesized NCs show a PL of 80% in spin-coated films but the post-synthesis treatment further enhances the efficiency >95%. The high PL is further confirmed by the monomolecular decay of the PL (5.8 ns) indicating a nearly complete suppression of non-radiative channels. The obtained films demonstrate high stability in air and require around 3 weeks to decrease to half the initial PL value.

Integrated circuits based on complementary metal-oxide–semiconductors (CMOS) are at the heart of the technological revolution of the past 40 years, enabling compact and low-cost microelectronic circuits and imaging systems. However, the diversification of this platform into applications other than microcircuits and visible-light cameras has been impeded by the difficulty to combine semiconductors other than silicon with CMOS. Here, we report the monolithic integration of a CMOS integrated circuit with graphene, operating as a high-mobility phototransistor. We demonstrate a high-resolution, broadband image sensor and operate it as a digital camera that is sensitive to ultraviolet, visible and infrared light (300–2,000 nm). The demonstrated graphene–CMOS integration is pivotal for incorporating 2D materials into the next-generation microelectronics, sensor arrays, low-power integrated photonics and CMOS imaging systems covering visible, infrared and terahertz frequencies. Graphene–quantum dots on CMOS sensor offers broadband imaging.

Lead sulphide (PbS) nanocrystals (NCs) are promising materials for low-cost, high-performance optoelectronic devices. So far, PbS NCs have to be first synthesized with long-alkyl chain organic surface ligands and then be ligand-exchanged with shorter ligands (two-steps) to enable charge transport. However, the initial synthesis of insulated PbS NCs show no necessity and the ligand-exchange process is tedious and extravagant. Herein, we have developed a direct one-step, scalable synthetic method for iodide capped PbS (PbS-I) NC inks. The estimated cost for PbS-I NC inks is decreased to less than 6 $·g−1, compared with 16 $·g−1 for conventional methods. Furthermore, based on these PbS-I NCs, photodetector devices show a high detectivity of 1.4 × 1011 Jones and solar cells show an air-stable power conversion efficiency (PCE) up to 10%. This scalable and low-cost direct preparation of high-quality PbS-I NC inks may pave a path for the future commercialization of NC based optoelectronics., Providing large-scale iodide capped semi-conductive PbS nanocrystals inks preparation for high-throughput manufacturing remains a challenge. Here, the authors propose a direct one step and scalable synthesis method enabling cost reduction and promoting its commercial viability for solar cells.

Flexible and transparent graphene photodetector technology allows non-invasive monitoring of vital signs., Wearable health and wellness trackers based on optical detection are promising candidates for public health uses due to their noninvasive tracking of vital health signs. However, so far, the use of rigid technologies hindered the ultimate performance and form factor of the wearable. Here, we demonstrate a new class of flexible and transparent wearables based on graphene sensitized with semiconducting quantum dots (GQD). We show several prototype wearable devices that are able to monitor vital health signs noninvasively, including heart rate, arterial oxygen saturation (SpO2), and respiratory rate. Operation with ambient light is demonstrated, offering low-power consumption. Moreover, using heterogeneous integration of a flexible ultraviolet (UV)–sensitive photodetector with a near-field communication circuit board allows wireless communication and power transfer between the photodetectors and a smartphone, offering battery-free operation. This technology paves the way toward seamlessly integrated wearables, and empowers the user through wireless probing of the UV index.

The turn-on voltage of a light-emitting diode (LED) is an important parameter as it determines the power consumption of the LED and influences the effective power conversion efficiency. LEDs based on nanoscale engineering of the blended PbS [mixture of quantum dots (QDs) with two different bandgaps] colloidal QDs have recently shown record performance in the infrared region. One of the most intriguing findings for these blended devices is the substantially lower-than-bandgap turn-on voltage and the achievement of an open circuit voltage ( V

Lead halide perovskite nanocrystals (NCs) are currently emerging as one of the most interesting solution-processed semiconductors because they possess high photoluminescence quantum yield (PLQY) and color tunability through anion exchange reactions or quantum confinement. Here, we show efficient solar cells based on mixed-halide (CsPbBrI2) NCs obtained via anion exchange reactions under ambient conditions. We performed anion exchange reactions in concentrated NC solutions with I–, thus inducing a PL red shift up to 676 nm and obtaining a high PLQY in film (65%). Solar cell devices operating in the wavelength range 350–660 nm were fabricated in air with two different deposition methods. The solar cells display a photoconversion efficiency of 5.3% and open circuit voltage (Voc) up to 1.31 V, among the highest reported for perovskite-based solar cells with band gap below 2 eV, clearly demonstrating the potential of this material.

Colloidal quantum dot (CQD) light-emitting diodes (LEDs) deliver a compelling performance in the visible, yet infrared CQD LEDs underperform their visible-emitting counterparts, largely due to their low photoluminescence quantum efficiency. Here we employ a ternary blend of CQD thin film that comprises a binary host matrix that serves to electronically passivate as well as to cater for an efficient and balanced carrier supply to the emitting quantum dot species. In doing so, we report infrared PbS CQD LEDs with an external quantum efficiency of ~7.9% and a power conversion efficiency of ~9.3%, thanks to their very low density of trap states, on the order of 1014 cm−3, and very high photoluminescence quantum efficiency in electrically conductive quantum dot solids of more than 60%. When these blend devices operate as solar cells they deliver an open circuit voltage that approaches their radiative limit thanks to the synergistic effect of the reduced trap-state density and the density of state modification in the nanocomposite. PbS quantum dot ternary blends enable the realization of high-efficiency colloidal quantum dot infrared light-emitting diodes

Indium tin oxide (ITO) is the most widely used transparent conductor in applications such as light emitting diodes, liquid crystal devices, touch screens, and photovoltaic cells. So far, its use has mainly been limited to the visible range (380 nm–750 nm), as it reflects at longer wavelengths and, consequently, its transmission is low. Here, we introduce a simple technique, based on high temperature annealing, which can reduce reflection in the near-infrared range (750 nm–2400 nm). With an optimized set of parameters, we were able to modulate the ITO properties and achieve a high transmission, greater than 80% including substrate contribution, at telecommunication wavelengths (C-band, 1530 nm–1565 nm) while still maintaining high electrical conductivity (resistivity, We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through Grant No. MAT2017-85232-R (AEI/FEDER, EU) and the Spanish State Research Agency through the “Severo Ochoa” program for Centers of Excellence in R&D (CEX2019-000910-S and CEX2019-000917 S), and project TUNA-SURF (Grant No. PID2019-106892RB-I00), from Fundació Cellex, Fundació Mir-Puig and from Generalitat de Catalunya through the CERCA program through AGAUR Grant Nos. 2017 SGR 1634 and 2017 301 SGR1377. C.G. acknowledges the funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 713729. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 754510. Y.C. acknowledges the China Scholarship Council (Grant No. 201506890029). The authors also acknowledge Vittoria Finazzi for her help and fruitful discussions.