Lead-Free Perovskite Semiconductors Based on Germanium-Tin Solid Solutions:Structural and Optoelectronic Properties

Solar cells and optoelectronics based on lead halide perovskites are generating considerable interest but face challenges with the use of toxic lead. In this study, we fabricate and characterize lead-free perovskites based on germanium and tin solid solutions, CH₃NH₃Sn_{(1–<i>x</i>)}Ge_<i>x</i>I₃ (0 ≤ <i>x</i> ≤ 1). We show that these perovskite compounds possess band gaps from 1.3 to 2.0 eV, which are suitable for a range of optoelectronic applications, from single junction devices and top cells for tandems to light-emitting layers. Their thermodynamic stability and electronic properties are calculated for all compositions and agree well with our experimental measurements. Our findings demonstrate an attractive family of lead-free perovskite semiconductors with a favorable band-gap range for efficient single-junction solar cells

Solution-processed Cd-substituted CZTS nanocrystals for sensitized liquid junction solar cells

The Earth-abundant kesterite Cu2ZnSnS4 (CZTS) exhibits outstanding structural, optical, and electronic properties for a wide range of optoelectronic applications. However, the efficiency of CZTS thin-film solar cells is limited due to range of factors, including electronic disorder, secondary phases, and the presence of anti-site defects, which is key factor limiting the Voc. The complete substitution of Zn lattice sites in CZTS nanocrystals (NCs) with Cd atoms offers a promising approach to overcome several of these intrinsic limitations. Herein, we investigate the effects of substitution of Cd2+ into Zn2+ lattice sites in CZTS NCs through a facile solution-based method. The structural, morphological, optoelectronic, and power conversion efficiencies (PCEs) of the NCs synthesized have been systematically characterized using various experimental techniques, and the results are corroborated by first-principles density functional theory (DFT) calculations. The successful substitution of Zn by Cd is demonstrated to induce a structural transformation from the kesterite phase to the stannite phase, which results in the bandgap reducing from 1.51 eV (kesterite) to 1.1 eV (stannite), which is closer to the optimum bandgap value for outdoor photovoltaic applications. Furthermore, the PCE of the novel Cd-substituted liquid junction solar cell underwent a four-fold increase, reaching 1.1%. These results highlight the importance of substitutional doping strategies in optimizing existing CZTS-based materials to achieve improved device characteristics

State of the Art and Prospects for Halide Perovskite Nanocrystals

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research. © 2021 American Chemical Society

High performance inverted bulk heterojunction solar cells by incorporation of dense, thin ZnO layers made using atmospheric atomic layer deposition

AbstractA thin ZnO (<200nm) film grown by Atmospheric Atomic Layer Deposition (AALD) in a matter of minutes was studied as a hole-blocking layer in poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-buyric acid methyl ester (P3HT:PCBM) based inverted solar cells. These AALD ZnO layers were compact, had a high electron mobility of 3.4+0.1cm2/Vs, had up to 100% transmittance to visible light, and a good wettability for the blend. Despite the very rapid, open atmosphere growth method, the cell performance was comparable with some of the best inverted bulk heterojunction P3HT:PCBM cells in the literature. The performance was also maintained after 200 days of storage in air in the dark

The ferro-pyro-phototronic effect for high-performance self-powered photodetectors

Self-powered photodetectors are advantageous over conventional photodetectors because they can have outstanding performance in the absence of an external power source, which is important for a range of applications, including in the Internet of Things. Current research has demonstrated different types of self-powered photodetectors utilizing the photovoltaic effect, pyroelectric effect, piezoelectric effect, and synergic effects, such as the piezo-phototronic and pyro-phototronic effects. Such effects have been demonstrated in standard semiconductors, in hybrid inorganic-organic halide perovskites and in all inorganic perovskites. Very recently, a novel type of self-powered photodetector exploring the coupling between the photovoltaic, the pyroelectric and the ferroelectric effects (i.e., ferro-pyro-phototronic effect) has attracted great interest, owing to the excellent photo current response achieved with this triple coupling. The ferro-pyro-phototronic effect can therefore be an important route towards improving the performance of self-powered photodetectors. Since ferroelectricity has the potential to bring revolutionary changes in many contemporary technologies, including non-volatile memory, solar cells, field effect transistors, energy storage, and energy harvesters, it is worthwhile exploring in more detail how the ferroelectric effect enhances the triple coupling. Thus, this focus review covers the research conducted so far on the ferro-pyro-phototronic effect, discussing recent progress on the development of self-powered photodetectors based on this effect, and also highlighting current challenges and potential solutions for using these devices in real-world applications.This work was supported by: (i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contracts UIDB/04650/2020, (ii) exploratory project 2022.01740. PDTC and (iii) the project M-ERA-NET3/0003/2021 - NanOx4EStor grant agreement No 958174 (https://doi.org/10.54499/M-ERA-NET3/0003/2021). J. P. B. S. also thanks FCT for the contract under the Institutional Call to Scientific Employment Stimulus – 2021 Call (CEECINST/00018/2021). JLM-D. and R.L.Z.H. thank EPSRC CAM-IES grant EP/P007767/. R.L.Z.H. also acknowledges support from the Royal Academy of Engineering under the Research Fellowships scheme (No.: RF\201718\1701). J.L.M-D. acknowledges support from the Royal Academy of Engineering Chair in Emerging Technologies scheme (No.: CIET1819_24) and the ERC Advanced Grant, ERC-ADG #882929 EROS. K. G. acknowledges support from the National Science Centre in Poland Grant No. 2023/07/X/ST7/00073

Wide-Bandgap Perovskite-Inspired Materials: Defect-Driven Challenges for High-Performance Optoelectronics

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Resolving electron and hole transport properties in semiconductor materials by constant light-induced magneto transport

The knowledge of minority and majority charge carrier properties enables controlling the performance of solar cells, transistors, detectors, sensors, and LEDs. Here, we developed the constant light induced magneto transport method which resolves electron and hole mobility, lifetime, diffusion coefficient and length, and quasi-Fermi level splitting. We demonstrate the implication of the constant light induced magneto transport for silicon and metal halide perovskite films. We resolve the transport properties of electrons and holes predicting the material’s effectiveness for solar cell application without making the full device. The accessibility of fourteen material parameters paves the way for in-depth exploration of causal mechanisms limiting the efficiency and functionality of material structures. To demonstrate broad applicability, we further characterized twelve materials with drift mobilities spanning from 10⁻³ to 10³ cm²V⁻¹s⁻¹ and lifetimes varying between 10⁻⁹ and 10⁻³ seconds. The universality of our method its potential to advance optoelectronic devices in various technological fields.ISSN:2041-172

Strong performance enhancement in lead-halide perovskite solar cells through rapid, atmospheric deposition of n-type buffer layer oxides

International audienceThin (approximately 10 nm) oxide buffer layers grown over lead-halide perovskite device stacks are critical for protecting the perovskite against mechanical and environmental damage. However, the limited perovskite stability restricts the processing methods and temperatures (≤110 °C) that can be used to deposit the oxide overlayers, with the latter limiting the electronic properties of the oxides achievable. In this work, we demonstrate an alternative to existing methods that can grow pinhole-free TiOx (x ~ 2) films with the requisite thickness in &lt;1 min without vacuum. This technique is atmospheric pressure chemical vapor deposition (AP-CVD). The rapid but soft deposition enables growth temperatures of ≥180 °C to be used to coat perovskites with or without a protective layer of PC61BM. This is ≥ 70 °C higher than achievable by current methods and results in more conductive TiOx films, boosting solar cell efficiencies by &gt;2%. Likewise, when AP-CVD SnOx (x ~ 2) is grown directly on the perovskite, there is also minimal structural damage to the underlying perovskite layer. The SnOx layer is pinhole-free and conformal. When used to cover perovskite devices with a PC61BM electron transport layer, shunting due to the pinholes in the spin-coated PC61BM is reduced, resulting in increases in the steady-state efficiency from 16.5% (no SnOx) to 19.4% (60 nm SnOx), with fill factors reaching 84%. This work shows AP-CVD to be a versatile technique for growing oxides on thermally-sensitive materials

Solution-processed Cd-substituted CZTS nanocrystals for sensitized liquid junction solar cells

The Earth-abundant kesterite Cu2ZnSnS4 (CZTS) exhibits outstanding structural, optical, and electronic properties for a wide range of optoelectronic applications. However, the efficiency of CZTS thin-film solar cells is limited due to a range of factors, including electronic disorder, secondary phases, and the presence of anti-site defects, which is a key factor limiting the Voc. The complete substitution of Zn lattice sites in CZTS nanocrystals (NCs) with Cd atoms offers a promising approach to overcome several of these intrinsic limitations. Herein, we investigate the effects of substituting Cd2+ into Zn2+ lattice sites in CZTS NCs through a facile solution-based method. The structural, morphological, optoelectronic, and power conversion efficiencies (PCEs) of the NCs synthesized have been systematically characterized using various experimental techniques, and the results are corroborated by first-principles density functional theory (DFT) calculations. The successful substitution of Zn by Cd is demonstrated to induce a structural transformation from the kesterite phase to the stannite phase, which results in the bandgap reduction from 1.51 eV (kesterite) to 1.1 eV (stannite), which is closer to the optimum bandgap value for outdoor photovoltaic applications. Furthermore, the PCE of the novel Cd-substituted liquid junction solar cell underwent a four-fold increase, reaching 1.1%. These results highlight the importance of substitutional doping strategies in optimizing existing CZTS-based materials to achieve improved device characteristics