Doping Control Via Molecularly Engineered Surface Ligand Coordination

Heo J.H., Im S.H., Noh J.H., Mandal T.N., Lim C., Chang J.A., Lee Y.H., Kim H., Sarkar A., Nazeeruddin M.K., Grätzel M., Seok S.I.

Inorganic‐organic hybrid structures have become innovative alternatives for next-generation dye-sensitized solar cells, because they combine the advantages of both systems. Here, we introduce a layered sandwich-type architecture, the core of which comprises a bicontinuous three-dimensional nanocomposite of mesoporous (mp)-TiO2 ,w ith CH 3NH3PbI3 perovskite as light harvester, as well as a polymeric hole conductor. This platform creates new opportunities for the development of low-cost, solution-processed, high-efficiency solar cells. The use of a polymeric hole conductor, especially poly-triarylamine, substantially improves the open-circuit voltage V oc and fill factor of the cells. Solar cells based on these inorganic‐organic hybrids exhibit a short-circuit current density Jsc of 16.5 mA cm 22 , Voc of 0.997 V and fill factor of 0.727, yielding a power conversion efficiency of 12.0% under standard AM 1.5 conditions.

Ball J.M., Lee M.M., Hey A., Snaith H.J.

We have reduced the processing temperature of the bulk absorber layer in CH3NH3PbI3−xClx perovskite solar cells from 500 to

Oh S.J., Berry N.E., Choi J., Gaulding E.A., Paik T., Hong S., Murray C.B., Kagan C.R.

We investigate the effects of stoichiometric imbalance on the electronic properties of lead chalcogenide nanocrystal films by introducing excess lead (Pb) or selenium (Se) through thermal evaporation. Hall-effect and capacitance-voltage measurements show that the carrier type, concentration, and Fermi level in nanocrystal solids may be precisely controlled through their stoichiometry. By manipulating only the stoichiometry of the nanocrystal solids, we engineer the characteristics of electronic and optoelectronic devices. Lead chalcogenide nanocrystal field-effect transistors (FETs) are fabricated at room temperature to form ambipolar, unipolar n-type, and unipolar p-type semiconducting channels as-prepared and with excess Pb and Se, respectively. Introducing excess Pb forms nanocrystal FETs with electron mobilities of 10 cm(2)/(V s), which is an order of magnitude higher than previously reported in lead chalcogenide nanocrystal devices. Adding excess Se to semiconductor nanocrystal solids in PbSe Schottky solar cells enhances the power conversion efficiency.

Ning Z., Zhitomirsky D., Adinolfi V., Sutherland B., Xu J., Voznyy O., Maraghechi P., Lan X., Hoogland S., Ren Y., Sargent E.H.

A novel approach to improving all-inorganic colloidal quantum dot (CQD) homojunction solar cells by engineering the doping spatial profile to produce a doping gradient within the n-type absorber is presented. The doping gradient greatly improves carrier collection and enhances the voltages attainable by the device, leading to a 1 power point power conversion efficiency (PCE) improvement over previous inorganic CQD solar cells.

Peruzzo A., Shadbolt P., Brunner N., Popescu S., O’Brien J.L.

Delaying Quantum Choice Photons can display wavelike or particle-like behavior, depending on the experimental technique used to measure them. Understanding this duality lies at the heart of quantum mechanics. In two reports, Peruzzo et al. (p. 634 ) and Kaiser et al. (p. 637 ; see the Perspective on both papers by Lloyd ) perform an entangled version of John Wheeler's delayed-choice gedanken experiment, in which the choice of detection can be changed after a photon passes through a double-slit to avoid the measurement process affecting the state of the photon. The original proposal allowed the wave and particle nature of light to be interchanged after the light had entered the interferometer. By contrast in this study, entanglement allowed the wave and particle nature to be interchanged after the light was detected and revealed the quantum nature of the photon, for example, it displays wave- and particle-like behavior simultaneously.

Etgar L., Gao P., Xue Z., Peng Q., Chandiran A.K., Liu B., Nazeeruddin M.K., Grätzel M.

We report for the first time on a hole conductor-free mesoscopic methylammonium lead iodide (CH(3)NH(3)PbI(3)) perovskite/TiO(2) heterojunction solar cell, produced by deposition of perovskite nanoparticles from a solution of CH(3)NH(3)I and PbI(2) in γ-butyrolactone on a 400 nm thick film of TiO(2) (anatase) nanosheets exposing (001) facets. A gold film was evaporated on top of the CH(3)NH(3)PbI(3) as a back contact. Importantly, the CH(3)NH(3)PbI(3) nanoparticles assume here simultaneously the roles of both light harvester and hole conductor, rendering superfluous the use of an additional hole transporting material. The simple mesoscopic CH(3)NH(3)PbI(3)/TiO(2) heterojunction solar cell shows impressive photovoltaic performance, with short-circuit photocurrent J(sc)= 16.1 mA/cm(2), open-circuit photovoltage V(oc) = 0.631 V, and a fill factor FF = 0.57, corresponding to a light to electric power conversion efficiency (PCE) of 5.5% under standard AM 1.5 solar light of 1000 W/m(2) intensity. At a lower light intensity of 100W/m(2), a PCE of 7.3% was measured. The advent of such simple solution-processed mesoscopic heterojunction solar cells paves the way to realize low-cost, high-efficiency solar cells.

Zhitomirsky D., Furukawa M., Tang J., Stadler P., Hoogland S., Voznyy O., Liu H., Sargent E.H.

N-type PbS colloidal-quantum-dot (CQD) films are fabricated using a controlled halide chemical treatment, applied in an inert processing ambient environment. The new materials exhibit a mobility of 0.1 cm2 V−1 s−1. The halogen ions serve both as a passivating agent and n-dope the films via substitution at surface chalcogen sites. The majority electron concentration across the range 1016 to 1018 cm−3 is varied systematically.

Voznyy O., Zhitomirsky D., Stadler P., Ning Z., Hoogland S., Sargent E.H.

We present a framework--validated using both modeling and experiment--to predict doping in CQD films. In the ionic semiconductors widely deployed in CQD films, the framework reduces to a simple accounting of the contributions of the oxidation state of each constituent, including both inorganic species and organic ligands. We use density functional theory simulations to confirm that the type of doping can be reliably predicted based on the overall stoichiometry of the CQDs, largely independent of microscopic geometrical bonding configurations. Studies employing field-effect transistors constructed from CQDs that have undergone various chemical treatments, coupled with Rutherford backscattering and X-ray photoelectron spectroscopy to provide compositional analysis, allow us to test and confirm the proposed model in an experimental framework. We investigate both p- and n-type electronic doping spanning a wide range of carrier concentrations from 10(16) cm(-3) to over 10(18) cm(-3), and demonstrate reversible switching between p- and n-type doping by changing the CQD stoichiometry. We show that the summation of the contributions from all cations and anions within the film can be used to predict accurately the majority carrier type. The findings enable predictable control over majority carrier concentration via tuning of the overall stoichiometry.

Todorov T.K., Tang J., Bag S., Gunawan O., Gokmen T., Zhu Y., Mitzi D.B.

Tang J., Liu H., Zhitomirsky D., Hoogland S., Wang X., Furukawa M., Levina L., Sargent E.H.

Colloidal quantum dot solids combine convenient solution-processing with quantum size effect tuning, offering avenues to high-efficiency multijunction cells based on a single materials synthesis and processing platform. The highest-performing colloidal quantum dot rectifying devices reported to date have relied on a junction between a quantum-tuned absorber and a bulk material (e.g., TiO2); however, quantum tuning of the absorber then requires complete redesign of the bulk acceptor, compromising the benefits of facile quantum tuning. Here we report rectifying junctions constructed entirely using inherently band-aligned quantum-tuned materials. Realizing these quantum junction diodes relied upon the creation of an n-type quantum dot solid having a clean bandgap. We combine stable, chemically compatible, high-performance n-type and p-type materials to create the first quantum junction solar cells. We present a family of photovoltaic devices having widely tuned bandgaps of 0.6–1.6 eV that excel where conventional quantum-to-bulk devices fail to perform. Devices having optimal single-junction bandgaps exhibit certified AM1.5 solar power conversion efficiencies of 5.4%. Control over doping in quantum solids, and the successful integration of these materials to form stable quantum junctions, offers a powerful new degree of freedom to colloidal quantum dot optoelectronics.

Graetzel M., Janssen R.A., Mitzi D.B., Sargent E.H.

Advances in solar photovoltaics are urgently needed to increase the performance and reduce the cost of harvesting solar power. Solution-processed photovoltaics are cost-effective to manufacture and offer the potential for physical flexibility. Rapid progress in their development has increased their solar-power conversion efficiencies. The nanometre (electron) and micrometre (photon) scale interfaces between the crystalline domains that make up solution-processed solar cells are crucial for efficient charge transport. These interfaces include large surface area junctions between photoelectron donors and acceptors, the intralayer grain boundaries within the absorber, and the interfaces between photoactive layers and the top and bottom contacts. Controlling the collection and minimizing the trapping of charge carriers at these boundaries is crucial to efficiency.

Nag A., Chung D.S., Dolzhnikov D.S., Dimitrijevic N.M., Chattopadhyay S., Shibata T., Talapin D.V.

Colloidal semiconductor nanocrystals (NCs) provide convenient "building blocks" for solution-processed solar cells, light-emitting devices, photocatalytic systems, etc. The use of inorganic ligands for colloidal NCs dramatically improved inter-NC charge transport, enabling fast progress in NC-based devices. Typical inorganic ligands (e.g., Sn(2)S(6)(4-), S(2-)) are represented by negatively charged ions that bind covalently to electrophilic metal surface sites. The binding of inorganic charged species to the NC surface provides electrostatic stabilization of NC colloids in polar solvents without introducing insulating barriers between NCs. In this work we show that cationic species needed for electrostatic balance of NC surface charges can also be employed for engineering almost every property of all-inorganic NCs and NC solids, including photoluminescence efficiency, electron mobility, doping, magnetic susceptibility, and electrocatalytic performance. We used a suite of experimental techniques to elucidate the impact of various metal ions on the characteristics of all-inorganic NCs and developed strategies for engineering and optimizing NC-based materials.

Engel J.H., Surendranath Y., Alivisatos A.P.

Semiconductor nanocrystal solids are attractive materials for active layers in next-generation optoelectronic devices; however, their efficient implementation has been impeded by the lack of precise control over dopant concentrations. Herein we demonstrate a chemical strategy for the controlled doping of nanocrystal solids under equilibrium conditions. Exposing lead selenide nanocrystal thin films to solutions containing varying proportions of decamethylferrocene and decamethylferrocenium incrementally and reversibly increased the carrier concentration in the solid by 2 orders of magnitude from their native values. This application of redox buffers for controlled doping provides a new method for the precise control of the majority carrier concentration in porous semiconductor thin films.

Ip A.H., Thon S.M., Hoogland S., Voznyy O., Zhitomirsky D., Debnath R., Levina L., Rollny L.R., Carey G.H., Fischer A., Kemp K.W., Kramer I.J., Ning Z., Labelle A.J., Chou K.W., et. al.

Colloidal quantum dot (CQD) films allow large-area solution processing and bandgap tuning through the quantum size effect. However, the high ratio of surface area to volume makes CQD films prone to high trap state densities if surfaces are imperfectly passivated, promoting recombination of charge carriers that is detrimental to device performance. Recent advances have replaced the long insulating ligands that enable colloidal stability following synthesis with shorter organic linkers or halide anions, leading to improved passivation and higher packing densities. Although this substitution has been performed using solid-state ligand exchange, a solution-based approach is preferable because it enables increased control over the balance of charges on the surface of the quantum dot, which is essential for eliminating midgap trap states. Furthermore, the solution-based approach leverages recent progress in metal:chalcogen chemistry in the liquid phase. Here, we quantify the density of midgap trap states in CQD solids and show that the performance of CQD-based photovoltaics is now limited by electron-hole recombination due to these states. Next, using density functional theory and optoelectronic device modelling, we show that to improve this performance it is essential to bind a suitable ligand to each potential trap site on the surface of the quantum dot. We then develop a robust hybrid passivation scheme that involves introducing halide anions during the end stages of the synthesis process, which can passivate trap sites that are inaccessible to much larger organic ligands. An organic crosslinking strategy is then used to form the film. Finally, we use our hybrid passivated CQD solid to fabricate a solar cell with a certified efficiency of 7.0%, which is a record for a CQD photovoltaic device.

Rath A.K., Bernechea M., Martinez L., de Arquer F.P., Osmond J., Konstantatos G.

In the last decade, solution-processed quantum dot/nanocrystal solar cells have emerged as a very promising technology for third-generation thin-film photovoltaics because of their low cost and high energy-harnessing potential. Quantum dot solar cell architectures developed to date have relied on the use of bulk-like thin films of colloidal quantum dots. Here, we introduce the bulk nano-heterojunction concept for inorganic solution-processed semiconductors. This platform can be readily implemented by mixing different semiconductor nanocrystals in solution and allows for the development of optoelectronic nanocomposite materials with tailored optoelectronic properties. We present bulk nano-heterojunction solar cells based on n-type Bi2S3 nanocrystals and p-type PbS quantum dots, which demonstrate a more than a threefold improvement in device performance compared to their bilayer analogue, as a result of suppressed recombination. The fabrication of nanoscale p–n junctions from colloidal nanocrystals and quantum dots provides a new architecture for efficient, solution-processed solar cells.

Ponomarenko Vladimir P., Popov Victor, Shuklov Ivan, Ivanov Victor V., Razumov Vladimir F.

Photosensing based on colloidal quantum dots (CQDs) is a rapidly developing area of infrared photoelectronics. The use of colloidal quantum dots markedly simplifies the manufacture, decreases the restrictions to the pixel pitch of the photosensitive elements, and reduces the production cost, which facilitates the wide use of IR sensors in various technological systems. This paper is the first exhaustive overeview of the architectures, methods of manufacturing and basic properties of photonic sensors based on colloidal quantum dots of compounds of Group II, IV and VI elements. Characteristic features of the synthesis and roles of the ligands and CQD morphology in the design of photosensors are considered in detail. The structures of photoresistive, photodiode and phototransistor elements based on HgTe, HgSe, PbS and PbSe CQDs, which are sensitive in various spectral ranges, are described. The main parameters of the most advanced optoelectronic devices based on colloidal quantum dot structures are presented. The key trends in the development of this area are analyzed.The bibliography includes 361 references.

Ahmed T., Kuo H., Lien D.

Colloidal quantum dots (CQDs) are nanocrystals synthesized in solution, boasting remarkable optical properties and notable electronic characteristics, such as size‐tunable bandgaps and high photoluminescence quantum yield. These features, coupled with solution processability, position CQDs as potential candidates for cost‐effective and high‐performance optoelectronic devices. However, several technological challenges hinder the full exploitation of CQDs in optoelectronics. Among these is the need for long insulating organic ligands in liquid‐phase synthesis, which restrict efficient charge injection and transport in quantum dot (QD) films. Furthermore, the high surface‐to‐volume ratios and core–shell structures prompt complexities in terms of doping and modifying electronic properties. The colloidal nature of quantum dots (QDs) also raises challenges regarding controlled deposition and patterning, which are critical for device fabrication. In this review, the imperative is outlined to tailor CQDs for optoelectronic applications, the limitations that obstruct the implementation of desired modifications are elaborated on, and the specific hurdles confronting electronic coupling, targeted doping, and precision patterning of CQDs are focused on. Additionally, herein, a summary of the solutions proposed to date is offered, insights are shared on the discussed topics, and areas warranting future investigation are highlighted.

Yu L., Tian P., Tang L., Hao Q., Teng K.S., Zhong H., Zuo W., Ji Y., Li H., Li Z., Ma Q., Yang M., Yu L.

Choi J., Si M., Kim S., Maniyamgama N., Kim D., Jee S., Kim Y.H., Jeong H., Kim B., Kim C., Lee J., Baek S.

Blending multiple functional nanoparticles (NPs) into one solvent and forming a stable hetero-ink is a promising technology to realize efficient solution-processed heterogeneous structures for next-generation energy conversion. However, differences in the surface nature of NPs hinder the formation of stable hybrid ink, causing unfavorable morphologies in film formation. In this work, we demonstrate a stable hybrid ink using colloidal quantum dots (CQDs) and metal-oxide NPs. The modified synthesis route of ZnO NPs enables modulation of their surfaces, resulting in ink that is fully miscible in alkyl amine solvents with CQDs. This hybrid ink allows the formation of conformal heterogeneous thin-films via a single step spin-casting. Based on this result, we devise an efficient planar-mixed heterojunction solar cell, which exhibits a 12.8% power conversion efficiency (PCE), one of the highest performances among prior CQD:metal-oxide hetero-structured hybrid solar cells.

Mamiyev Z., Balayeva N.O.

The primary motivation behind efforts to understand the properties of lead sulfide (PbS) is its technological importance as the foundation of modern semiconductor optoelectronics. PbS nanocrystals (NCs) show remarkable versatility and promise for application in both conventional optical devices and the new generation of nano-electronics and nano-optoelectronics because of their particular structure and size-related properties. Although PbS NCs have been the subject of intense fundamental and applied studies, no comprehensive evaluation of the published data has been documented so far. Undoubtedly, providing an overview of the published research will help further development in PbS-related research and will certainly make it a step forward in the application. Therefore, this review paper discusses the preparation, structural, electronic and optical properties of PbS NCs in light of recent progress in nanotechnology. We first survey the fundamental properties of PbS NCs and then mainly focus on size-dependent properties. In this regard, the recent breakthrough in tuning the properties of PbS NCs employing doping, ligands, capping and hybridizing with different materials, and interaction with embedded media has been particularly discussed. The review concludes with the enhanced performance of the PbS NCs towards future optoelectronic devices and biological and chemical applications.

Meng L., Wang X.

Colloidal semiconductor nanocrystals have generated tremendous interest because of their solution processability and robust tunability. Among such nanocrystals, the colloidal quantum dot (CQD) draws the most attention for its well-known quantum size effects. In the last decade, applications of CQDs have been booming in electronics and optoelectronics, especially in photovoltaics. Electronically doped semiconductors are critical in the fabrication of solar cells, because carefully designed band structures are able to promote efficient charge extraction. Unlike conventional semiconductors, diffusion and ion implantation technologies are not suitable for doping CQDs. Therefore, researchers have creatively developed alternative doping methods for CQD materials and devices. In order to provide a state-of-the-art summary and comprehensive understanding to this research community, we focused on various doping techniques and their applications for photovoltaics and demystify them from different perspectives. By analyzing two classes of CQDs, lead chalcogenide CQDs and perovskite CQDs, we compared different working scenarios of each technique, summarized the development in this field, and raised our own future perspectives.

Zhou R., Xu J., Luo P., Hu L., Pan X., Xu J., Jiang Y., Wang L.

Semiconductor quantum dots (QDs) are nanocrystals whose excitons are bound in 3D space. Owning to their remarkable quantum confinement effect, QDs exhibit a discontinuous electronic energy level structure similar to that of atoms, leading to novel physical, optical, and electrical properties for various optoelectronic device applications including solar cells. Near-infrared photoactive narrow bandgap (NBG) QDs can maximize the use of solar energy through the quantum size effect, offering a good opportunity for designing highly efficient wide-spectrum responsive solar cells. This review analyzes the recent research progress of NBG QDs as light absorbing materials in solar cells. The critical elaboration of the latest achievements both in material design and device optimization for NBG QD-based solar cells (QDSCs), including QD synthesis and film fabrication, design of device configuration, classification of NBG QDs and their photovoltaic performance, strategies for performance improvements is focused upon. The current challenges and perspectives for the further advance of NBG QDSCs are also discussed.

Bellani S., Bartolotta A., Agresti A., Calogero G., Grancini G., Di Carlo A., Kymakis E., Bonaccorso F.

In the ever-increasing energy demand scenario, the development of novel photovoltaic (PV) technologies is considered to be one of the key solutions to fulfil the energy request. In this context, graphene and related two-dimensional (2D) materials (GRMs), including nonlayered 2D materials and 2D perovskites, as well as their hybrid systems, are emerging as promising candidates to drive innovation in PV technologies. The mechanical, thermal, and optoelectronic properties of GRMs can be exploited in different active components of solar cells to design next-generation devices. These components include front (transparent) and back conductive electrodes, charge transporting layers, and interconnecting/recombination layers, as well as photoactive layers. The production and processing of GRMs in the liquid phase, coupled with the ability to “on-demand” tune their optoelectronic properties exploiting wet-chemical functionalization, enable their effective integration in advanced PV devices through scalable, reliable, and inexpensive printing/coating processes. Herein, we review the progresses in the use of solution-processed 2D materials in organic solar cells, dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic–inorganic hybrid solar cells, as well as in tandem systems. We first provide a brief introduction on the properties of 2D materials and their production methods by solution-processing routes. Then, we discuss the functionality of 2D materials for electrodes, photoactive layer components/additives, charge transporting layers, and interconnecting layers through figures of merit, which allow the performance of solar cells to be determined and compared with the state-of-the-art values. We finally outline the roadmap for the further exploitation of solution-processed 2D materials to boost the performance of PV devices.

Liu J., Xian K., Ye L., Zhou Z.

Lead chalcogenide colloidal quantum dot solar cells (CQDSCs) have received considerable attention due to their broad and tunable absorption and high stability. Presently, lead chalcogenide CQDSC has achieved a power conversion efficiency of ≈14%. However, the state-of-the-art lead chalcogenide CQDSC still has an open-circuit voltage (Voc) loss of ≈0.45 V, which is significantly higher than those of c-Si and perovskite solar cells. Such high Voc loss severely limits the performance improvement and commercialization of lead chalcogenide CQDSCs. In this review, the Voc loss is first analyzed via detailed balance theory and the origin of Voc loss from both solar absorber and interface is summarized. Subsequently, various strategies for improving the Voc from the solar absorber, including the passivation strategies during the synthesis and ligand exchange are overviewed. The great impact of the ligand exchange process on CQD passivation is highlighted and the corresponding strategies to further reduce the Voc loss are summarized. Finally, various strategies are discussed to reduce interface Voc loss from charge transport layers. More importantly, the great potential of achieving performance breakthroughs via various organic hole transport layers is highlighted and the existing challenges toward commercialization are discussed.

Kim T., Lim S., Yun S., Jeong S., Park T., Choi J.

Quantum dots (QDs) are emerging photovoltaic materials that display exclusive characteristics that can be adjusted through modification of their size and surface chemistry. However, designing a QD-based optoelectronic device requires specialized approaches compared with designing conventional bulk-based solar cells. In this paper, design considerations for QD thin-film solar cells are introduced from two different viewpoints: optics and electrics. The confined energy level of QDs contributes to the adjustment of their band alignment, enabling their absorption characteristics to be adapted to a specific device purpose. However, the materials selected for this energy adjustment can increase the light loss induced by interface reflection. Thus, management of the light path is important for optical QD solar cell design, whereas surface modification is a crucial issue for the electrical design of QD solar cells. QD thin-film solar cell architectures are fabricated as a heterojunction today, and ligand exchange provides suitable doping states and enhanced carrier transfer for the junction. Lastly, the stability issues and methods on QD thin-film solar cells are surveyed. Through these strategies, a QD solar cell study can provide valuable insights for future-oriented solar cell technology.

Lee S., Choi M., Sharma G., Biondi M., Chen B., Baek S., Najarian A.M., Vafaie M., Wicks J., Sagar L.K., Hoogland S., de Arquer F.P., Voznyy O., Sargent E.H.

Surface ligands enable control over the dispersibility of colloidal quantum dots (CQDs) via steric and electrostatic stabilization. Today’s device-grade CQD inks have consistently relied on highly polar solvents: this enables facile single-step deposition of multi-hundred-nanometer-thick CQD films; but it prevents the realization of CQD film stacks made up of CQDs having different compositions, since polar solvents redisperse underlying films. Here we introduce aromatic ligands to achieve process-orthogonal CQD inks, and enable thereby multifunctional multilayer CQD solids. We explore the effect of the anchoring group of the aromatic ligand on the solubility of CQD inks in weakly-polar solvents, and find that a judicious selection of the anchoring group induces a dipole that provides additional CQD-solvent interactions. This enables colloidal stability without relying on bulky insulating ligands. We showcase the benefit of this ink as the hole transport layer in CQD optoelectronics, achieving an external quantum efficiency of 84% at 1210 nm. The realisation of film made up of different compositions using colloidal QD inks remains a challenge because of redispersing of underlying films by polar solvents. Here, the authors introduce aromatic ligands to achieve QD inks in weakly-polar solvents that enable fabrication of multi-compositional films.

Kim H.I., Lee J., Choi M., Ryu S.U., Choi K., Lee S., Hoogland S., Arquer F.P., Sargent E.H., Park T.

Kirmani A.R., Walters G., Kim T., Sargent E.H., Amassian A.

Progress in chalcogenide and perovskite CQD optoelectronics has relied to a significant extent on solid-state ligand exchanges (SSEs): the replacement of initial insulating ligands with shorter con...

Liu Y., Zhao X., Yang Z., Li Q., Wei W., Hu B., Chen W.

Perovskite solar cells (PSCs) have developed rapidly in the past 10 years. However, they are faced with a huge challenge for stability improvement because of the volatile organic components in the ...

Yang X., Yang J., Khan J., Deng H., Yuan S., Zhang J., Xia Y., Deng F., Zhou X., Umar F., Jin Z., Song H., Cheng C., Sabry M., Tang J.

The recent emerging progress of quantum dot ink (QD-ink) has overcome the complexity of multiple-step colloidal QD (CQD) film preparation and pronouncedly promoted the device performance. However, the detrimental hydroxyl (OH) ligands induced from synthesis procedure have not been completely removed. Here, a halide ligand additive strategy was devised to optimize QD-ink process. It simultaneously reduced sub-bandgap states and converted them into iodide-passivated surface, which increase carrier mobility of the QDs films and achieve thicker absorber with improved performances. The corresponding power conversion efficiency of this optimized device reached 10.78%. (The control device was 9.56%.) Therefore, this stratege can support as a candidate strategy to solve the QD original limitation caused by hydroxyl ligands, which is also compatible with other CQD-based optoelectronic devices.