Query: Strongly emissive perovskite nanocrystal inks for high-voltage solar cells

Candidate papers:

abstract: Lead halide perovskite semiconductors have recently gained wide interest following their successful embodiment in solid state photovoltaic devices with impressive power conversion efficiencies, while offering a relatively simple and low cost processability. Although the primary optoelectronic properties of these materials have already met the requirement for high efficiency optoelectronic technologies, industrial scale up requires more robust processing methods, as well as solvents that are less toxic than the ones that have been commonly used so successfully on the lab scale. Here we report a fast, room temperature synthesis of inks based on CsPbBr3 perovskite nanocrystals using short, low boiling point ligands and environmentally friendly solvents. Requiring no lengthy post synthesis treatments, the inks are directly used to fabricate films of high optoelectronic quality, exhibiting photoluminescence quantum yields higher than 30% and an amplified spontaneous emission threshold as low as 1.5 mJ cm 2. Finally, we demonstrate the fabrication of perovskite nanocrystal based solar cells, with open circuit voltages as high as 1.5 V. Despite their impressive performance, more efforts are required to develop industrially scalable perovskite solar cells from less toxic solvents. Towards that aim, this study presents the use of colloidal nanoparticle inks for room temperature fabrication of CsPbBr3 solar cells.
author_names: Quinten A Akkerman

Marina Gandini

Francesco Di Stasio

Prachi Rastogi

Francisco Palazon

Giovanni Bertoni

James M Ball

Mirko Prato

Annamaria Petrozza

Liberato Manna
title: Strongly emissive perovskite nanocrystal inks for high voltage solar cells
year: 2017

abstract: The morphology of hybrid perovskite thin films depends strongly on the processing parameters due to its complex crystallization kinetics from a solution to solid perovskite halide phase. It is also profoundly sensitive to the device area of the deposited thin film, and hence reproducible photoconversion efficiency (PCE) remained a bottleneck for the fabrication of efficient photovoltaic devices having large active area. The present work focuses on the investigations of the relationship between perovskite ink concentration dependent quality of the perovskite overlayer and PCE of the perovskite solar cells (PSC) while scaling up process. The field emission scanning electron microscopy images revealed that the surface coverage of perovskite overlayer depends on the concentration of perovskite solution and device area. The active area dependent current density (J) voltage (V) and external quantum efficiency measurements identify morphology dependent variation in charge transport/recombination pathways. We confirmed that among different precursor concentrations, 40 wt% perovskite ink is suitable to produce uniform perovskite overlayer over 1 cm2. As a result, highly reproducible PCE 13% has been achieved for the PSC having an active area of 1 cm2. Overall, our findings significantly provide new insights into the active area dependent PCE of PSC.
author_names: Arif D Sheikh

Akhilesh P Patil

Sawanta S Mali

Chang Kook Hong

Pramod S Patil
title: New insights into active area dependent performance of hybrid perovskite solar cells
venue: Journal of Materials Science
year: 2019

abstract: Author(s) Sarang, Som Advisor(s) Ghosh, Sayantani Abstract: In just over a decade, perovskite semiconductors have shown immense promise as candidates for next generation opto electronic technologies, attributed to broad absorption spectra, long recombination lifetimes, ambipolar charge carrier conductivity and impressive electron mobility. Perovskite photovoltaics(PV) with power conversion efficiencies g 23% is challenging existing solar cell technologies and have revolutionized the field of solution processed solar cells. However, several drawbacks arising from perovskite stability and scalability have prevented them from achieving their full potential. The scope of this dissertation is to address some of these concerns, while also shedding light into the atypical physical properties of Perovskite semiconductors. The first part of the thesis deals with developing a rapid thoroughput and scalable fabrication route for perovskite thin film solar cells, utilizing an electro hydrodynamic spraying route inspired from 'Marangoni flow' seen in nature. The fabricated perovskite solar cells had superior current voltage characteristics and displayed an efficiency of g 16% which at the time (2015) was one of the highest reported power conversion efficiencies. Additionally, the developed fabrication method requires lower amounts of precursor solvents compared to other scalable approaches, thus reducing Lead wastage and mitigating environmental issues often associated with perovskite solar cells. Following this project, a range of low temperature, ultrafast optical spectroscopy techniques were used to probe the partial phase transitions in Perovskite thin films. This revealed charge migration pathways in perovskite thin films at low temperatures that prove detrimental for their device performance. In parallel, our experiments showed that the phase transition is associated with a crossover from excitonic to free charge carrier recombination in perovskite thin films.The above results encouraged us to investigate nanocrystals of perovskite semiconductors, aiming to achieve better crystal phase stability at low temperatures. We successfully quenched partial crystal phase transitions at low temperatures in perovskite quantum dots utilizing ligand based surface modification techniques. These findings highlighted aspects of perovskite phase stability linked to nanoscale morphology, paving way for improved perovskite devices operating at low temperatures.Lastly, the potential of perovskite quantum dots in spintronics applications were explored. We demonstrated optical spin polarization in perovskite quantum dots and measured their spin lifetimes using Hanle effect. In addition, Manganese ion dopants in Ruddlesden Popper perovskite quantum dots exhibited polarized photoluminescence emission attributed to strong exchange interactions In conclusion, we successfully developed high performing perovskite PV devices and demonstrated their plausible application in other opto electronic technologies, while also shedding light into its interesting physical properties.
author_names: Som Sarang
title: Perovskite semiconductors: From high performance devices to optical characterization
year: 2019

abstract: The slowdown of carrier cooling in lead halide perovskites (LHP) may allow the realization of efficient hot carrier solar cells. Much of the current effort focuses on the understanding of the mechanisms that retard the carrier relaxation, while proof of principle demonstrations of hot carrier harvesting have started to emerge. Less attention has been placed on the impact that the energy and momentum relaxation slowdown imparts on the spontaneous and stimulated light emission process. LHP nanocrystals (NCs) provide an ideal testing ground for such studies as they exhibit bright emission and high optical gain, while the carrier cooling bottleneck is further pronounced compared to their bulk analogues due to confinement. Herein, the luminescent properties of CsPbBr3, FAPbBr3, and FAPbI3 NCs in the strong photoexcitation regime are investigated. In the former two NC systems, amplified spontaneous emission is found to dominate over the radiative recombination at average carrier occupancy per nanocrystal larger than 5 10. On the other hand, under the same photoexcitation conditions in the FAPbI3 NCs, a longer lived population of hot carriers results in a competition between hot luminescence, stimulated emission, and defect recombination. The dynamic interplay between the aforementioned three emissive channels appears to be influenced by various experimental and material parameters that include temperature, material purity, film morphology, and excitation pulse width and wavelength.
author_names: Paris Papagiorgis

Andreas Manoli

Sozos Michael

Caterina Bernasconi

Maryna I Bodnarchuk

Maksym V Kovalenko

Andreas Othonos

Grigorios Itskos
title: Unraveling the Radiative Pathways of Hot Carriers upon Intense Photoexcitation of Lead Halide Perovskite Nanocrystals.
venue: ACS nano
year: 2019

abstract: Abstract Organolead halide perovskite with excellent optoelectronic properties, which endows its potential applications in versatile optoelectronic device including solar cells and photodetectors. In spite of great efforts made on the perovskite photodetectors, novel device configurations based on perovskite films have to be explored to further improve the performance. Here, we present perovskite photodetectors enabled by a novel metal (Al) oxide semiconductor (perovskite) (MOS) structure. The unique photodetector can work on a wide voltage range and exhibits extreme characteristics with a pA scale dark current, and a high detectivity >1014 Jones) Both ultralow dark and light currents enable the small power consumption output ~nW under 2 mW cm 2 at 2 V. The C V data analysis proves that the charge carriers are accumulated at the oxide/perovskite interface, which leads to the reduction of the conduct band offset. At a low voltage the current transport behaviors for the MOS structure photodetectors are dominated by the Ohm's Law, while at a high voltage, the main mechanism is Schottky emission which is demonstrated by temperature dependence I V measurements. Our results strongly propose the use of perovskite based photodetectors with a unique MOS structure in the application of optoelectronic devices.
author_names: Yuming Zhang

Kai Sun

Ziyang Hu

Yuejin Zhu

Renxu Jia
title: Organolead halide perovskite based metal oxide semiconductor structure photodetectors achieving ultrahigh detectivity
venue: Solar Energy
year: 2019

abstract: We present a cation exchange approach for tunable A site alloys of cesium (Cs+ and formamidinium (FA+ lead triiodide perovskite nanocrystals that enables the formation of compositions spanning the complete range of Cs1 xFA xPbI3, unlike thin film alloys or the direct synthesis of alloyed perovskite nanocrystals. These materials show bright and finely tunable emission in the red and near infrared range between 650 and 800 nm. The activation energy for the miscibility between Cs+ and FA+ is measured ~0.65 eV) and is shown to be higher than reported for X site exchange in lead halide perovskites. We use these alloyed colloidal perovskite quantum dots to fabricate photovoltaic devices. In addition to the expanded compositional range for Cs1 xFA xPbI3 materials, the quantum dot solar cells exhibit high open circuit voltage VOC) with a lower loss than the thin film perovskite devices of similar compositions.
author_names: Abhijit Hazarika

Qian Zhao

E Ashley Gaulding

Jeffrey A Christians

Benjia Dou

Ashley R Marshall

Taylor Moot

Joseph J Berry

Justin C Johnson

Joseph M Luther
title: Perovskite Quantum Dot Photovoltaic Materials beyond the Reach of Thin Films: Full Range Tuning of A Site Cation Composition.
venue: ACS nano
year: 2018

abstract: Metal halide perovskites (MHPs) are of great interest for optoelectronics because of their high quantum efficiency in solar cells and light emitting devices. However, exploring an effective strategy to further improve their optical activities remains a considerable challenge. Here, we report that nanocrystals (NCs) of the initially nonfluorescent zero dimensional (0D) cesium lead halide perovskite Cs4PbBr6 exhibit a distinct emission under a high pressure of 3.01 GPa. Subsequently, the emission intensity of Cs4PbBr6 NCs experiences a significant increase upon further compression. Joint experimental and theoretical analyses indicate that such pressure induced emission (PIE) may be ascribed to the enhanced optical activity and the increased binding energy of self trapped excitons upon compression. This phenomenon is a result of the large distortion of [PbBr6]4 octahedral motifs resulting from a structural phase transition. Our findings demonstrate that high pressure can be a robust tool to boost the photoluminescence efficiency and provide insights into the relationship between the structure and optical properties of 0D MHPs under extreme conditions.The potential optoelectronic applications of metal halide perovskites make exploration and tuning of their optical properties of great interest. Here the authors show that non emitting zero dimensional cesium lead halide perovskites become strongly fluorescent under high pressure, due to distortion induced effects.
author_names: Zhiwei Ma

Zhun Liu

Siyu Lu

Lei Wang

Xiaolei Feng

Dongwen Yang

Kai Wang

Guanjun Xiao

Lijun Zhang

Simon A T Redfern

Bo Zou
title: Pressure induced emission of cesium lead halide perovskite nanocrystals
venue: Nature Communications
year: 2018

abstract: Perovskite nanocrystals have shown themselves to be useful for both absorption and emission based applications, including solar cells, photodetectors, and LEDs. Here we present a new class of size composition and shape tunable nanocrystals made from Tl3PbX5 (X= Cl, Br, I) These can be synthesized via colloidal methods to produce faceted spheroidal nanocrystals, and perovskite TlPbI3 nanowires. Crystal structures for the orthorhombic and tetragonal phase materials, for both pure and mixed halide species, are compared to the literature and also calculated from first principles in VASP. We show the ability to tune the band gap by halide substitution to create materials that can absorb strongly between 250 and 450 nm. In addition, we show evidence of the confinement effect in pure halide Tl3PbBr5 nanocrystals suggesting size tuning is possible as well. By tuning the band gap we can create materials with specific absorption spectra suitable for photodetection that display conduction and photoresponse pro.
author_names: Parth Vashishtha

Dani Z Metin

Matthew E Cryer

Kai Chen

Justin M Hodgkiss

Nicola Gaston

Jonathan E Halpert
title: Shape Size and Composition Controlled Thallium Lead Halide Perovskite Nanowires and Nanocrystals with Tunable Band Gaps
year: 2018

abstract: Colloidal semiconductor nanocrystals (NCs) also known as colloidal quantum dots (QDs) have played an indispensable role in the development of modern nanoscience and nanotechnology because of their unique optical and electronic properties, and they are still being intensively investigated for various potential applications. Semiconductor NCs offer significant advantages over conventional organic fluorescent dyes, including the tunability of emission color by their size and composition, excellent color purity, ease of preparation and controllable surface chemistry enabling their dispersion in various solvents for solution processability. As a consequence, the past two decades have witnessed tremendous progress in the shape controlled synthesis, self assembly, surface functionalization and optoelectronic device applications of II VI and III V semiconductor QDs. Recently, metal halide perovskites have emerged as a new class of semiconductor material with extraordinary optical and electronic properties. Perovskite materials of the form APbX3 (with A as the inorganic or organic cation, and X Cl, Br, or I) have been well known since the late 1970s from the work by Weber. They became popular after the first report on halide perovskite solar cells in 2009 by Kojima et al. Since then, halide perovskites have created large excitement in the photovoltaic research community that was stimulated by a meteoric rise in the power conversion efficiency of perovskite solar cells from 3.8% to over 22% in a short development time. In addition, the outstanding optical properties of perovskites have made them excellent light sources for applications in LEDs, photodetectors, photo transistors and lasers. The early studies on perovskites were focused on the optimization of bulk films for device applications. Despite the rapid progress in perovskite materials in photovoltaics and optoelectronics, the properties that make them so special, like their tolerance to defects, are yet to be fully understood. From the II VI and III V semiconductor materials, we know that colloidal nanocrystals offer several advantages over their bulk counterparts, including solution processability, enhanced photoluminescence efficiency and tunable emission through quantum confinement effects. The first solution phase colloidal synthesis of organic inorganic hybrid perovskite NCs was published in 2014 by Perez Prieto et al. A year later, Kovalenko et al. reported the colloidal synthesis of all inorganic perovskite NCs. Since then, metal halide perovskite NCs have received significant research interest due to their extraordinary optical properties as well as their appeal as emitters in efficient light sources. The unique feature of perovskite NCs is that they exhibit near unity photoluminescence quantum yield (PLQY) without the need of a core shell architecture, unlike the conventional QDs (e.g. CdSe/CdS/ZnS and CdSe/ZnSe/ZnS core multi shell NCs) The emission color of perovskite NCs is easily tunable across the visible spectrum by the halide composition and by confinement effects. Like in conventional colloidal systems, ligands play a crucial role in the shape and size control of perovskite NCs, and also in the passivation of surface defects, which is decisive for high PLQY. In the last few years, we have witnessed extremely rapid progress in the synthesis of perovskite NCs of a wide range of morphologies and shapes, such as quantum dots, nanocubes, nanowires, nanorods, nanoplatelets, and nanosheets. In fact, it is possible to control the dimensions of NCs with monolayer precision, which leads to strong tunability of the band gap in nanowires, nanoplatelets and nanosheets. Introducing organic molecules as spacer layers in between the octahedral planes enabled the fabrication of layered perovskites with a large band gap and emission at a wavelength of around 400 nm, which can be tuned Chair for Photonics and Optoelectronics, NanoInstitute Munich, Department of Physics, LudwigMaximilians Universitat (LMU) Koniginstr. 10, 80539 Munich, Germany. E mail: l.polavarapu@lmu.de Institute of Functional Nano and Soft Materials (FUNSOM) Jiangsu Key Laboratory for Carbon Based Functional Materials and Devices, Soochow University, China. E mail: qiaozhang@suda.edu.cn Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy. E mail: Roman.Krahne@iit.it
author_names: Lakshminarayana Polavarapu

Qiao Zhang

Roman Krahne
title: Nanoscale Nanoscale Advances joint themed collection on halide perovskite nanocrystals.
venue: Nanoscale
year: 2019

abstract: A rational design and construction of white light emitting components based on semiconductor materials are extremely important in lighting and display technologies.[1 4] In general, there are two reasonable approaches developed to realize the white light source. They are the synthesis of semiconductor alloy nanostructures with widely tunable band gaps,[5 7] and the construction of a white lighting emitter with various single band gap semiconductors that have monochromatic luminescence with high quantum efficiency.[8 10] However, white light generated from red green blue emitters based on semiconductor nanostructures has been known as the major challenge in the solid state lighting community.[1,2,8,9] For example, a suitable mix for white light radiation with favorable wavelengths and intensity ratios, proper color rendering index, and high stability is still lacking.[11,12] Recently, perovskite materials have brought a variety of new opportunities for the advancement of nanophotonics and optoelectronics.[13 23] In particular, inorganic metal halide perovskites, such as cesium lead halide perovskites, have drawn enormous attention because they show great promises for various photoelectric applications, such as the natural highquality whispering gallery mode (WGM) or Fabry Perot (F P) resonators,[16,17,24 26] laser cooling,[18] solar cells,[27 30] and light emitting diodes.[31 33] Moreover, they also exhibit a broad band gap tunability for multifunctional devices and circuits covering the entire visible spectrum.[19,20] Therefore, these unusual semiconductor materials may offer the opportunity to design novel white light emitting devices in future full color displays. Currently, solution based synthesis methods have been commonly used to realize the band gap tunable cesium lead halide perovskite (CsPbX3, X Cl, Br, I) quantum dots.[34 37] Protesescu et al. reported a new avenue for the growth of CsPbX3 perovskite nanocrystals by the solution phase method, which shows bright emissions with a wide color gamut.[38] In comparison, chemical vapor deposition (CVD) is another attractive approach for the synthesis of diverse Wavelength tunable nano/microlasers are essential components for various highly integrated and multifunctional photonic devices. Based on the different band gap/composition of inorganic cesium lead halide perovskite materials, broad band light absorption and emission devices can be achieved. Herein, a vapor liquid solid route for growing cesium lead halide perovskite (CsPbX3, X Cl, Br, I) microcrystal structures is demonstrated. These square shaped microstructures exhibit strong blue, green, and red photoluminescence, indicating that their band gaps can be engineered to cover the entire visible range. Optically pumped red green blue whispering gallery mode lasers based on the controlled composition of these microcrystals are successfully realized at room temperature. Moreover, rationally designed white light emitting chips with high brightness are fabricated utilizing these metal halide perovskite microstructures grown on sapphire. All these results evidently suggest a feasible route to the design of red green blue lasers and white light emitters for potential applications in full color displays as well as photonic devices. Perovskite Microlasers
author_names: Pengfei Guo

Mohammad Kamal Hossain

Xia Shen

Haibin Sun

Wenchao Yang

Chao Liu

Chun Yuen Ho

Cheuk Kai Gary Kwok

Sai-Wing Tsang

Yongsong Luo

Johnny C Ho

Kin Man Yu
title: Room Temperature Red Green Blue Whispering Gallery Mode Lasing and White Light Emission from Cesium Lead Halide Perovskite (CsPbX3, X Cl, Br, I) Microstructures
year: 2018