Efficiency of the quantum dots based solar cells relies on charge transfer at the interface and hence on the relative alignment of the energy levels between materials. Despite a high demand to obtain size specific band offsets, very few studies exist where meticulous methods like photoelectron spectroscopy are used. However, semiconductor charging during measurements could result in indirect and possibly inaccurate measurements due to shift in valence and conduction band position. Here, in this report, we devise a novel method to study the band offsets by associating an atomic like state with the conduction band and hence obtaining an internal standard. This is achieved by doping copper in semiconductor nanocrystals, leading to the development of a characteristic intragap Cu-related emission feature assigned to the transition from the conduction band to the atomic-like Cu d state. Using this transition we determine the relative band alignment of II-VI semiconductor nanocrystals as a function of size in the below 10 nm size regime. The results are in excellent agreement with the available photoelectron spectroscopy data as well as the theoretical data. We further use this technique to study the excitonic band edge variation as a function of temperature in CdSe nanocrystals. Additionally, surface electronic structure of CdSe nanocrystals have been studied using quantitative measurements of absolute quantum yield and PL decay studies of the Cu related emission and the excitonic emission. The role of TOP and oleic acid as surface passivating ligand molecules has been studied for the first time.

Lead‐free perovskite‐inspired materials (PIMs) are gaining attention in optoelectronics due to their low toxicity and inherent air stability. Their wide bandgaps (≈2 eV) make them ideal for indoor light harvesting. However, the investigation of PIMs for indoor photovoltaics (IPVs) is still in its infancy. Herein, the IPV potential of a quaternary PIM, Cu2AgBiI6 (CABI), is demonstrated upon controlling the film crystallization dynamics via additive engineering. The addition of 1.5 vol% hydroiodic acid (HI) leads to films with improved surface coverage and large crystalline domains. The morphologically‐enhanced CABI+HI absorber leads to photovoltaic cells with a power conversion efficiency of 1.3% under 1 sun illumination—the highest efficiency ever reported for CABI cells and of 4.7% under indoor white light‐emitting diode lighting—that is, within the same range of commercial IPVs. This work highlights the great potential of CABI for IPVs and paves the way for future performance improvements through effective passivation strategies.

In this Letter, we report the study of the effect of ligands on the surface electronic structure of the nanocrystal by exploiting the mechanism of the Cu-related optical transition, obtained by coupling the nanocrystal conduction band to the Cu ion state in Cu-doped II-VI semiconductor nanocrystals. Systematic study of steady-state luminescence and lifetime decay dynamics of this Cu-related emission in cadmium-based chalcogenides shows that the role of oleic acid in surface passivation is unexpectedly quite different for various chalcogenides. Further, using these leads in Cu-doped CdS nanocrystals, we develop near-infrared-emitting phosphor materials that have tunable, high quantum yield (∼35%) emission with a single-exponential lifetime decay. Surprisingly, unlike the emission from other Cu-doped II-VI nanocrystals, emission from Cu doping in CdS nanocrystals is found to exhibit high thermal stability, being essentially unchanged up to 100 °C, making them more viable for use in various practical applications.

Double perovskites are a promising family of lead-free materials that not only replace lead but also enable new optoelectronic applications beyond photovoltaics. Recently, a titanium (Ti)-based vacancy-ordered double perovskite, Cs2TiBr6, has been reported as an example of truly sustainable and earth-abundant perovskite with controversial results in terms of photoluminescence and environmental stability. Our work looks at this material from a new perspective, i.e., at the nanoscale. We demonstrate the first colloidal synthesis of Cs2TiX6 nanocrystals (X = Br, Cl) and observe tunable morphology and size of the nanocrystals according to the set reaction temperature. The Cs2TiBr6 nanocrystals synthesized at 185 °C show a bandgap of 1.9 eV and are relatively stable up to 8 weeks in suspensions. However, they do not display notable photoluminescence. The centrosymmetric crystal structure of Cs2TiBr6 suggests that this material could enable third-harmonic generation (THG) responses. Indeed, we provide a clear evidence of THG signals detected by the THG microscopy technique. As only a few THG-active halide perovskite materials are known to date and they are all lead-based, our findings promote future research on Cs2TiBr6 as well as on other lead-free double perovskites, with stronger focus on currently unexplored nonlinear optical applications.

Cesium copper halides (CCHs) show promise for optoelectronic applications, and their syntheses usually involve high-temperatures and hazard solvents. Herein, the synthesis of highly luminescent and phase-pure Cs 3 Cu 2 X 5 (X = Cl, Br, and I) and CsCu 2 I 3 via a solvent-free mechanochemical approach through manual grinding is demonstrated. This costeffective approach can produce CCHs on a scale of tens to hundreds of grams. Rietveld refinement analysis of the X-ray diffraction patterns of the as-synthesized CCHs reveals their structural details. Notably, the emission characteristics of green-emitting, chloride-based CCHs remain stable even at elevated temperaturesmaintaining 80% of initial PL efficiency at 150 °C. Lastly, a postsynthetic reversible transformation between zero-and one-dimensional CCH materials is demonstrated, indicating the labile nature of their crystal structure. The proposed study suggests that mechanochemistry can be an alternative and promising synthetic tool for fabricating high-quality lead-free metal halides.

FETs), light-emitting diodes (LED), solar cells, water splitting, and water purification owing to their exceptional electronic and optical properties such as extreme absorption coefficient, robust photoluminescence, extended carrier diffusion length, ambipolar charge transport, defect tolerant nature, and similar effective mass value. [1-9] Mitzi et al. reported tin-based perovskites as a new family of semiconductors in 1994. [10] However, real attention was captured only in 2009, when Kojima et al. successfully used them in solar cells as a sensitizer in a dye-sensitized solar cell (DSSC) with the power conversion efficiency (PCE) of 3.8%. [11] Recently, other groups demonstrated halide perovskites as solid-state PSCs with 10% efficiency, which provided considerable impetus for the field, together with the recent spectacular rise in PCE (25.2% certified). [12,13] Apart from solar cells, perovskite halides have been successfully implemented in optoelectronic devices such as FETs and LEDs. [14-17] However, the structural features of perovskites experience swift degradation under different stress conditions such as moisture, UV light, oxygen, and high temperature, which limits their practical applications. [18] This drawback can be tackled by stabilizing halide perovskites by various approaches such as integration of multiple capping agents/stabilizers and encapsulation into various porous materials like polymer matrices, polymethyl Metal halide perovskites (MHPs) have excellent optoelectronic and photovoltaic applications because of their cost-effectiveness, tunable emission, high photoluminescence quantum yields, and excellent charge carrier properties. However, the potential applications of the entire MHP family are facing a major challenge arising from its weak resistance to moisture, polar solvents, temperature, and light exposure. A viable strategy to enhance the stability of MHPs could lie in their incorporation into a porous template. Metal-organic frameworks (MOFs) have outstanding properties, with a unique network of ordered/functional pores, which render them promising for functioning as such a template, accommodating a wide range of MHPs to the nanosized region, alongside minimizing particle aggregation and enhancing the stability of the entrapped species. This review highlights recent advances in design strategies, synthesis, characterization, and properties of various hybrids of MOFs with MHPs. Particular attention is paid to a critical review of the emergence of MHP@MOF for comprehensive studies of next-generation materials for various technological applications including sensors, photocatalysis, encryption/decryption, light-emitting diodes, and solar cells. Finally, by summarizing the state-of-the-art, some promising future applications of reported hybrids are proposed. Considering the inherent correlation and synergic functionalities of MHPs and MOFs, further advancement; new functional materials; and applications can be achieved through designing MHP@MOF hybrids.

The role of ligands in passivating quantum dots has been studied in this work using Cu doping as internal sensors. This has been elucidated using the example of dodecanethiol, 3-mercaptopropionic acid, trioctylphosphine, trioctylphosphine oxide, and primary amines for the passivation of CdSe quantum dots by exchanging the original ligands. Steady state and time dependent photoluminescence spectra of the Cu emission have provided the basis for determining the role of ligands. The surface of the quantum dots with ligand exchange has been monitored using nuclear magnetic resonance spectroscopy. The results suggest that the presence of trioctylphosphine, trioctylphosphine oxide, and oleylamine ligands on CdSe quantum dot surface lead to better photoluminescence efficiency. Further, increase in the chain length of the primary amines increases the effectiveness of passivation on the CdSe quantum dot surface. We have also extended this method to the study of oleylamine capping in CdS quantum dots.

Antimony‐based perovskite‐inspired materials (PIMs) are solution‐processable halide absorbers with interesting optoelectronic properties, low toxicity, and good intrinsic stability. Their bandgaps around 2 eV make them particularly suited for indoor photovoltaics (IPVs). Yet, so far only the fully inorganic Cs3Sb2ClxI9−x composition has been employed as a light‐harvesting layer in IPVs. Herein, the first triple‐cation Sb‐based PIM (CsMAFA‐Sb) in which the A‐site of the A3Sb2X9 structure consists of inorganic cesium alloyed with organic methylammonium (MA) and formamidinium (FA) cations is introduced. Simultaneously, the X‐site is tuned to guarantee a 2D structure while keeping the bandgap nearly unchanged. The presence of three A‐site cations is essential to reduce the trap‐assisted recombination pathways and achieve high performance in both outdoor and indoor photovoltaics. The external quantum efficiency peak of 77% and the indoor power conversion efficiency of 6.4% are the highest values ever reported for pnictohalide‐based photovoltaics. Upon doping of the P3HT hole‐transport layer with F4‐TCNQ, the power conversion efficiency of CsMAFA‐Sb devices is fully retained compared to the initial value after nearly 150 days of storage in dry air. This work provides an effective compositional strategy to inspire new perspectives in the PIM design for IPVs with competitive performance and air stability.