I07-Surface & interface diffraction
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Elena J.
Cassella
,
Emma L. K.
Spooner
,
Joel A.
Smith
,
Timothy
Thornber
,
Mary E.
O'Kane
,
Robert D. J.
Oliver
,
Thomas E.
Catley
,
Saqlain
Choudhary
,
Christopher J.
Wood
,
Deborah B.
Hammond
,
Henry J.
Snaith
,
David G.
Lidzey
Diamond Proposal Number(s):
[30612]
Open Access
Abstract: High temperature post-deposition annealing of hybrid lead halide perovskite thin films—typically lasting at least 10 min—dramatically limits the maximum roll-to-roll coating speed, which determines solar module manufacturing costs. While several approaches for “annealing-free” perovskite solar cells (PSCs) have been demonstrated, many are of limited feasibility for scalable fabrication. Here, this work has solvent-engineered a high vapor pressure solvent mixture of 2-methoxy ethanol and tetrahydrofuran to deposit highly crystalline perovskite thin-films at room temperature using gas-quenching to remove the volatile solvents. Using this approach, this work demonstrates p-i-n devices with an annealing-free MAPbI3 perovskite layer achieving stabilized power conversion efficiencies (PCEs) of up to 18.0%, compared to 18.4% for devices containing an annealed perovskite layer. This work then explores the deposition of self-assembled molecules as the hole-transporting layer without annealing. This work finally combines the methods to create fully annealing-free devices having stabilized PCEs of up to 17.1%. This represents the state-of-the-art for annealing-free fabrication of PSCs with a process fully compatible with roll-to-roll manufacture.
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Feb 2023
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I07-Surface & interface diffraction
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Margherita
Taddei
,
Joel A.
Smith
,
Benjamin M.
Gallant
,
Suer
Zhou
,
Robert J. E.
Westbrook
,
Yangwei
Shi
,
Jian
Wang
,
James N.
Drysdale
,
Declan P.
Mccarthy
,
Stephen
Barlow
,
Seth R.
Marder
,
Henry J.
Snaith
,
David S.
Ginger
Diamond Proposal Number(s):
[30612]
Abstract: We show that adding ethylenediamine (EDA) to perovskite precursor solutions improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA1–xCsxPb(I1–yBry)3, which are currently of interest for perovskite-on-Si tandem solar cells. Using spectroscopy and hyperspectral microscopy, we show that the additive improves film homogeneity and suppresses the phase instability that is ubiquitous in high-Br perovskite formulations, producing films that remain stable for over 100 days in ambient conditions. With the addition of 1 mol % EDA, we demonstrate 1.69 eV-gap perovskite single-junction p-i-n devices with a VOC of 1.22 V and a champion maximum-power-point-tracked power conversion efficiency of 18.8%, comparable to the best reported methylammonium-free perovskites. Using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction techniques, we show that EDA reacts with FA+ in solution, rapidly and quantitatively forming imidazolinium cations. It is the presence of imidazolinium during crystallization which drives the improved perovskite thin-film properties.
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Nov 2022
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B23-Circular Dichroism
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Jessica
Wade
,
Francesco
Salerno
,
Rachel C.
Kilbride
,
Dong Kuk
Kim
,
Julia A.
Schmidt
,
Joel A.
Smith
,
Luc M.
Leblanc
,
Emma H.
Wolpert
,
Adebayo A.
Adeleke
,
Erin R.
Johnston
,
Jenny
Nelson
,
Tadashi
Mori
,
Kim E.
Jelfs
,
Sandrine
Heutz
,
Matthew J.
Fuchter
Diamond Proposal Number(s):
[29151]
Abstract: Chiral π-conjugated molecules bring new functionality to technological applications and represent an exciting, rapidly expanding area of research. Their functional properties, such as the absorption and emission of circularly polarized light or the transport of spin-polarized electrons, are highly anisotropic. As a result, the orientation of chiral molecules critically determines the functionality and efficiency of chiral devices. Here we present a strategy to control the orientation of a small chiral molecule (2,2′-dicyano[6]helicene) by the use of organic and inorganic templating layers. Such templating layers can either force 2,2′-dicyano[6]helicene to adopt a face-on orientation and self-assemble into upright supramolecular columns oriented with their helical axis perpendicular to the substrate, or an edge-on orientation with parallel-lying supramolecular columns. Through such control, we show that low- and high-energy chiroptical responses can be independently ‘turned on’ or ‘turned off’. The templating methodologies described here provide a simple way to engineer orientational control and, by association, anisotropic functional properties of chiral molecular systems for a range of emerging technologies.
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Oct 2022
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[18563]
Open Access
Abstract: The addition of alkali metal halides to hybrid perovskite materials can significantly impact their crystallisation and hence their performance when used in solar cell devices. Previous work on the use of potassium iodide (KI) in active layers to passivate defects in triple-cation mixed-halide perovskites has been shown to enhance their luminescence efficiency and reduce current–voltage hysteresis. However, the operational stability of KI passivated perovskite solar cells under ambient conditions remains largely unexplored. By investigating perovskite solar cell performance with SnO2 or TiO2 electron transport layers (ETL), we propose that defect passivation using KI is highly sensitive to the composition of the perovskite–ETL interface. We reconfirm findings from previous reports that KI preferentially interacts with bromide ions in mixed-halide perovskites, and – at concentrations >5 mol% in the precursor solution – modifies the primary absorber composition as well as leading to the phase segregation of an undesirable secondary non-perovskite phase (KBr) at high KI concentration. Importantly, by studying both material and device stability under continuous illumination and bias under ambient/high-humidity conditions, we show that this secondary phase becomes a favourable degradation product, and that devices incorporating KI have reduced stability.
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Nov 2020
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[18563]
Abstract: Solvent vapour annealing (SVA) is a common post-processing technique used to increase the average grain size of lead halide perovskite films and thus enhance device performance. The prevailing wisdom is that large grain perovskite films lead to enhanced stability, however, we observed the reverse in CH3NH3PbI3 (MAPbI3) with dimethylformamide vapour treatment compared to non-SVA controls. Using a range of microstructural characterisation techniques, we reveal that SVA is not a chemically benign grain-growth process, but leads to substantial stoichiometric changes in the perovskite films. Intrinsic material degradation is investigated under external loading with in situ X-ray scattering, and combined with lifetime testing on full devices. We show that the operational stability of SVA devices greatly depends on the initial stoichiometry of the MAPbI3 with PbI2-excess compositions being least stable. However, the incorporation of excess organic-halides in the precursor solution helps to mitigate the deleterious effects of SVA on device stability. This work critically re-evaluates current thinking around grain structure and stoichiometry in achieving long-term stability for perovskite solar cells.
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Jun 2020
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I07-Surface & interface diffraction
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Donghui
Li
,
Xiaolong
Chen
,
Jinglong
Cai
,
Wei
Li
,
Mengxue
Chen
,
Yuchao
Mao
,
Baocai
Du
,
Joel A.
Smith
,
Rachel C.
Kilbride
,
Mary E.
O'Kane
,
Xue
Zhang
,
Yuan
Zhuang
,
Pang
Wang
,
Hui
Wang
,
Dan
Liu
,
Richard A. L.
Jones
,
David G.
Lidzey
,
Tao
Wang
Diamond Proposal Number(s):
[22651]
Abstract: Optimizing the components and morphology within the photoactive layer of organic solar cells (OSCs) can significantly enhance their power conversion efficiency (PCE). A new A-D-A type non-fullerene acceptor IDMIC-4F is designed and synthesized in this work, and is employed as the third component to prepare high performance ternary solar cells. IDMIC-4F can form fibrils after solution casting, and the presence of this fibrillar structure in the PBDB-T-2F:BTP-4F host confines the growth of donors and acceptors into fine domains, as well as acting as transport channels to enhance electron mobility. Single junction ternary devices incorporating 10 wt% IDMIC-4F exhibit enhanced light absorption and balanced carrier mobility, and achieve a maximum PCE of 16.6% compared to 15.7% for the binary device, which is a remarkable efficiency for OSCs reported in literature. This non-fullerene acceptor fibril network strategy is a promising method to improve the photovoltaic performance of ternary OSCs.
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Feb 2020
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I07-Surface & interface diffraction
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Wei
Li
,
Zuo
Xiao
,
Joel As.
Smith
,
Jinlong
Cai
,
Donghui
Li
,
Rachel C.
Kilbride
,
Emma L. K.
Spooner
,
Onkar S.
Game
,
Xianyi
Meng
,
Dan
Liu
,
Richard A. L.
Jones
,
David G.
Lidzey
,
Liming
Ding
,
Tao
Wang
Diamond Proposal Number(s):
[20419]
Abstract: Traditional single-junction binary organic solar cells suffer from narrow absorption windows, limiting their ability to harvest photons. One promising approach to avoid this issue is through the construction of a ternary system to enhance the spectral response and efficiency. However, the complex morphology and photophysical processes within ternary blends leave the criteria of an effective third component unclear, and so they remain a challenge. In this work, we report on the fabrication of PTB7-Th:COi8DFIC-based ternary solar cells with enhanced efficiency by employing either a polymer donor or a nonfullerene acceptor as the third component. We demonstrate that the third component is highly associated with the condensed state of the host acceptor and is the primary factor in determining efficiency improvement. The π-π stacking molecular packing of COi8DFIC helps to maintain the optimal phase separation within the ternary blends and improves both the hole and electron charge mobilities, resulting in enhanced power conversion efficiency of over 14%, compared to 13.1% in binary devices. We also found an excessive amount of polymer donor or nonfullerene acceptor increases the phase separation and encourages lamellar crystallization with the host acceptor domain, resulting in reduced light-harvesting and external quantum efficiencies at long wavelengths. Our results provide a rational guide to selecting the third component to fabricate high-performance nonfullerene-based ternary solar cells.
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Dec 2019
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I07-Surface & interface diffraction
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Baocai
Du
,
Renyong
Geng
,
Wei
Li
,
Donghui
Li
,
Yuchao
Mao
,
Mengxue
Chen
,
Xue
Zhang
,
Joel A.
Smith
,
Rachel C.
Kilbride
,
Mary E.
O'Kane
,
Dan
Liu
,
David G.
Lidzey
,
Weihua
Tang
,
Tao
Wang
Diamond Proposal Number(s):
[22651]
Abstract: The insufficient phase separation between polymer donors and non-fullerene acceptors (NFAs) featuring with low-structural orders disrupts efficient charge transport and increases charge recombination, consequently limits the maximum achievable power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, an NFA IT-M has been added as the third component into the PBDB-T:m-INPOIC OSCs, and is shown to effectively tune the phase separation between donor and acceptor molecules, although all components in the ternary system exhibit low degrees of structural orders. The incorporation of 10 wt% IT-M into a PBDB-T:m-INPOIC binary host blend appreciably increases the length scale of phase separation, creating continuous pathways which increase and balance charge transport. This leads to an enhanced photovoltaic performance from 12.8% in the binary cell to 13.9% for the ternary cell with simultaneously improved open-circuit voltage, short-circuit current and fill factor. This work highlights the beneficial role of ternary components in controlling the morphology of the active layer for high performance OSCs.
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Sep 2019
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I07-Surface & interface diffraction
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Wei
Li
,
Zuo
Xiao
,
Jinlong
Cai
,
Joel A.
Smith
,
Emma L. K.
Spooner
,
Rachel C.
Kilbride
,
Onkar S.
Game
,
Xianyi
Meng
,
Donghui
Li
,
Huijun
Zhang
,
Mengxue
Chen
,
Robert S.
Gurney
,
Dan
Liu
,
Richard A. L.
Jones
,
David
Lidzey
,
Liming
Ding
,
Tao
Wang
Diamond Proposal Number(s):
[120419]
Abstract: The chemical structure of non-fullerene acceptors (NFAs) affects their light-harvesting capabilities, energy levels and molecular orders, all of which play a crucial role in determining the efficiency of organic solar cells (OSCs). In this work, we have systematically investigated a series of ladder-type NFAs having different carbon-oxygen-bridged electron-donating cores, and revealed the effects of core structures and film casting conditions on molecular ordering and performance of OSCs. We found that NFAs containing the thieno [3,2-b]thiophene centered, 6 or 8 fused rings (i.e. COi6DFIC, COi8DFIC) exhibit narrower optical band gaps than NFAs containing the benzene centered, 5 or 7 fused rings (i.e. COi5DFIC, COi7DFIC). NFAs containing less fused rings in the carbon-oxygen-bridged core (i.e. COi5DFIC and COi6DFIC) exhibit edge-on molecular orientation in the blends with face-on oriented PTB7-Th donor, and result in low device efficiency. Although NFAs containing more fused rings (i.e. COi7DFIC and COi8DFIC) possess a pronounced flat-on lamellar crystalline structure in the pure state, the crystallization can be reduced when blending with PTB7-Th and under hot-substrate casting, while the lamella in COi8DFIC can be effectively suppressed to form face-on H- and J-type aggregates, leading to enhanced efficiency.
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Jul 2019
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