27 research outputs found
Lead-free perovskite-inspired semiconductors for indoor light-harvesting - the present and the future
G. K. G. thanks Tampere Institute for Advanced Study for the postdoctoral funding. P. V. and V. S. acknowledge the financial support of Jane and Aatos Erkko foundation (SOL-TECH project) and Academy of Finland (Decision No. 347772). B.A-A. thanks Vilho, Yrjö and Kalle Väisälä Fund of the Finnish Academy of Science and Letters for the financial support. This work is part of the Academy of Finland Flagship Programme, Photonics Research and Innovation (PREIN), Decision No. 320165.Are lead-free perovskite-inspired materials (PIMs) the wise choice for efficient yet sustainable indoor light harvesting? This feature article outlines how wide-bandgap PIMs can provide a positive answer to this compelling question. The wide band gaps can hinder sunlight absorption, in turn limiting the solar cell performance. However, PIMs based on group VA of the periodic table can theoretically lead to an outstanding indoor power conversion efficiency up to 60% when their band gap is ∼2 eV. Yet, the research on PIM-based indoor photovoltaics (IPVs) is still in an early stage with highest indoor device efficiencies up to 10%. This article reviews the recent advancements on PIMs for IPVs and identifies the main limiting factors of device performance, thus suggesting effective strategies to address them. We emphasize the poor operational stability of the IPV devices of PIMs being the key bottleneck for the vast adoption of this technology. We believe that this report can provide a solid scaffolding for further researching this fascinating class of materials, ultimately supporting our vision that, upon extensive advancement of the stability and efficiency, PIMs with wide bandgap will become a contender for the next-generation absorbers for sustainable indoor light harvesting.Publisher PDFPeer reviewe
Role of Self-Trapped Excitons in the Broadband Emission of Lead-Free Perovskite-Inspired Cu2AgBiI6
publishedVersionPeer reviewe
Enhancing the Microstructure of Perovskite-Inspired Cu-Ag-Bi-I Absorber for Efficient Indoor Photovoltaics
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.</p
Surface and optical properties of phase-pure silver iodobismuthate nanocrystals
The study of surface defects is one of the forefronts of halide perovskite research. In the nanoscale regime, where the surface-to-volume ratio is high, the surface plays a key role in determining the electronic properties of perovskites. Perovskite-inspired silver iodobismuthates are promising photovoltaic absorbers. Herein, we demonstrate the colloidal synthesis of phase pure and highly crystalline AgBiI4 nanocrystals (NCs). Surface-sensitive spectroscopic techniques reveal the rich surface features of the NCs that enable their impressive long-term environmental and thermal stabilities. Notably, the surface termination and its passivation effects on the electronic properties of AgBiI4 are investigated. Our atomistic simulations suggest that a bismuth iodide-rich surface, as in the case of AgBiI4 NCs, does not introduce surface trap states within the band gap region of AgBiI4, unlike a silver iodide-rich surface. These findings may encourage the investigation of surfaces of other lead-free perovskite-inspired materials.publishedVersionPeer reviewe
Antimony-Bismuth Alloying : The Key to a Major Boost in the Efficiency of Lead-Free Perovskite-Inspired Photovoltaics
The perovskite-inspired Cu2AgBiI6 (CABI) material has been gaining increasing momentum as photovoltaic (PV) absorber due to its low toxicity, intrinsic air stability, direct bandgap, and a high absorption coefficient in the range of 105 cm−1. However, the power conversion efficiency (PCE) of existing CABI-based PVs is still seriously constrained by the presence of both intrinsic and surface defects. Herein, antimony (III) (Sb3+) is introduced into the octahedral lattice sites of the CABI structure, leading to CABI-Sb with larger crystalline domains than CABI. The alloying of Sb3+ with bismuth (III) (Bi3+) induces changes in the local structural symmetry that dramatically increase the formation energy of intrinsic defects. Light-intensity dependence and electron impedance spectroscopic studies show reduced trap-assisted recombination in the CABI-Sb PV devices. CABI-Sb solar cells feature a nearly 40% PCE enhancement (from 1.31% to 1.82%) with respect to the CABI devices mainly due to improvement in short-circuit current density. This work will promote future compositional design studies to enhance the intrinsic defect tolerance of next-generation wide-bandgap absorbers for high-performance and stable PVs.Peer reviewe
Tunable Infrared Phosphors Using Cu Doping in Semiconductor Nanocrystals: Surface Electronic Structure Evaluation
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
Demystifying Complex Quantum Dot Heterostructures Using Photogenerated Charge Carriers
The
success of heterostructure quantum dots in optoelectronic and
photovoltaic applications is based on our understanding of photogenerated
charge carrier localization. However, often the actual location of
charge carriers in heterostructure semiconductors is quite different
from their predicted positions leading to suboptimal results. In this
work, photoluminescence of Cu doped heterostructures has been used
to study the charge localization of alloys, inverse type I, type II,
and quasi type II core/shell structures and graded alloys. Specifically,
the adeptness of this method has been assessed over a range of widely
studied heterostructures like CdSe/CdS, CdS/CdSe, CdSe/CdTe, Zn<sub>1–<i>x</i></sub>Cd<sub><i>x</i></sub>Se
and Zn<sub>1–<i>x</i></sub>Cd<sub><i>x</i></sub>S quantum dots systems by doping them with a small percentage
of Cu. The electron and hole localization obtained from this method
concurs with the pre-existing understanding in cases that have been
explored before, while the internal structure of previously unknown
heterostructures have been predicted
Copper Doping in II–VI Semiconductor Nanocrystals: Single-Particle Fluorescence Study
Copper doping in II–VI semiconductor nanocrystals (NCs) has sparked enormous debate regarding the oxidation state of Cu ions and their hugely differing consequences in optoelectronic applications. The identity of a magnetically active Cu ion or a magnetically inactive d Cu ion has generally been probed using optical techniques, and confusion arises from the spatial clutter that is part of the technique. One major probe that could declutter the data obtained from ensemble emission is single-particle fluorescence spectroscopy. In this work, using this very technique along with X-ray absorption spectroscopy probing the local environment of dopant ions, we study Cu-doped II–VI semiconductor NCs to find conclusive evidence on the oxidation state of Cu dopants and hence the mechanism of their emission. Detailed analysis of blinking properties has been used to study the single-particle nature of the NCs
Study of the Interface and Radial Dopant Position in Semiconductor Heterostructures Using X‑ray Absorption Spectroscopy
Two questions that remain a challenge
in the field of
colloidal
doped core/shell nanomaterials of different morphologies are the nature
of the interface and the radial location of the dopant ion due to
the diffusion within the lattice. Using a model system of Cu-doped
CdSe/CdS quantum dots, we develop an in-depth understanding of the
extended X-ray absorption fine structure (EXAFS) spectra of the dopant
and host atoms to address both issues. Our findings suggest that the
interface is not sharp, in agreement with the nonstructural studies
in the literature. Local structure analysis around the Cu dopant ion
confirms that Cu drifts out from the core toward the outer region
in the absence of the shell but stays mostly in the core after the
formation of a sufficiently thick interfacial barrier (∼2 monolayers).
This study highlights the significance of EXAFS spectroscopy in understanding
the nature of the interface in nanomaterials
Study of the Interface and Radial Dopant Position in Semiconductor Heterostructures Using X‑ray Absorption Spectroscopy
Two questions that remain a challenge
in the field of
colloidal
doped core/shell nanomaterials of different morphologies are the nature
of the interface and the radial location of the dopant ion due to
the diffusion within the lattice. Using a model system of Cu-doped
CdSe/CdS quantum dots, we develop an in-depth understanding of the
extended X-ray absorption fine structure (EXAFS) spectra of the dopant
and host atoms to address both issues. Our findings suggest that the
interface is not sharp, in agreement with the nonstructural studies
in the literature. Local structure analysis around the Cu dopant ion
confirms that Cu drifts out from the core toward the outer region
in the absence of the shell but stays mostly in the core after the
formation of a sufficiently thick interfacial barrier (∼2 monolayers).
This study highlights the significance of EXAFS spectroscopy in understanding
the nature of the interface in nanomaterials