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Spiro Ometad Synthesis Essay

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Unbound MEDLINE: Enhancing the hole-conductivity of spiro-OMeTAD without oxygen or lithium salts by using spiro(TFSI)₂ in perovskite and dye-sensiti

Enhancing the hole-conductivity of spiro-OMeTAD without oxygen or lithium salts by using spiro(TFSI)₂ in perovskite and dye-sensitized solar cells. Abstract

2,2',7,7'-Tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD), the prevalent organic hole transport material used in solid-state dye-sensitized solar cells and perovskite-absorber solar cells, relies on an uncontrolled oxidative process to reach appreciable conductivity. This work presents the use of a dicationic salt of spiro-OMeTAD, named spiro(TFSI)2, as a facile means of controllably increasing the conductivity of spiro-OMeTAD up to 10(-3) S cm(-1) without relying on oxidation in air. Spiro(TFSI)2 enables the first demonstration of solid-state dye-sensitized solar cells fabricated and operated with the complete exclusion of oxygen after deposition of the sensitizer with higher and more reproducible device performance. Perovskite-absorber solar cells fabricated with spiro(TFSI)2 show improved operating stability in an inert atmosphere. Gaining control of the conductivity of the HTM in both dye-sensitized and perovskite-absorber solar cells in an inert atmosphere using spiro(TFSI)2 is an important step toward the commercialization of these technologies.

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Facile synthesis of fluorene-based hole transport materials for highly efficient perovskite solar cells and solid-state dye-sensitized solar cells
  • Yong Hua a,1
  • Jinbao Zhang b,1
  • Bo Xu a
  • Peng Liu c
  • Ming Cheng a
  • Lars Kloo c
  • Erik M.J. Johansson b
  • Kári Sveinbjörnsson b
  • Kerttu Aitola b
  • Gerrit Boschloo b,.
  • Licheng Sun a,d,.
  • a Organic Chemistry, Center of Molecular Devices, Department of Chemistry, Chemical Science and Engineering, KTH Royal Institute of Technology, 10044 Stockholm, Sweden
  • b Physical Chemistry, Centre of Molecular Devices, Department of Chemistry–Ångström Laboratory, Uppsala University, 75120 Uppsala, Sweden
  • c Applied Physical Chemistry, School of Chemical Science and Engineering, Department of Chemistry, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden
  • d State Key Laboratory of Fine Chemicals, DUT-KTH Joint Research Centre on Molecular Devices, Dalian University of Technology (DUT), 116024 Dalian, China

Received 13 March 2016. Revised 30 April 2016. Accepted 3 May 2016. Available online 9 May 2016.

Highlights

Fluorene-based hole transport materials (HTMs) have been designed and applied in perovskite solar cells (PSCs) and solid-state dye-sensitized solar cell (ssDSCs).

The new HTMs were prepared through a facile two-step reaction in a total yield higher than 90%.

Devices with HT2 as HTM showed high PCEs of 18.04% in PSCs and 6.35% in ssDSCs under 100 mW cm −2 AM1.5 G solar illumination.

More extended three-dimensional structure and higher molecular weight of HTMs enable better photovoltaic performance.

Abstract

Two novel low-cost fluorene-based hole transport materials (HTMs) HT1 and HT2 as alternatives to the expensive HTM Spiro-OMeTAD have been designed and synthesized for the application in perovskite solar cells (PSCs) and solid-state dye-sensitized solar cell (ssDSCs). The two HTMs were prepared through a facile two-step reaction from cheap starting material and with a total yield higher than 90%. These HTMs exhibit good solubility and charge-transport ability. PSCs based on HT2 achieved power conversion efficiency (PCE) of 18.04% under air conditions, which is comparable to that of the cell employing the commonly used Spiro-OMeTAD (18.27%), while HT1 -based cell showed a slightly worse performance with a PCE of 17.18%. For ssDSCs, the HT2 -based device yielded a PCE of 6.35%, which is also comparable to that of a cell fabricated based on Spiro-OMeTAD (6.36%). We found that the larger dimensional structure and molecular weight of HT2 enable better photovoltaic performance than that of the smaller one HT1. These results show that easily synthesized fluorene-based HTMs have great potential to replace the expensive Spiro-OMeTAD for both PSCs and ssDSCs.

Graphical abstract

Keywords
  • Fluorene
  • Hole-transport material
  • Perovskite solar cells
  • Solid-state dye sensitized solar cell

Scheme 1. Fig. 1. Fig. 2.

Table 1. Fig. 3. Fig. 4.

Vitae

Yong Hua received his Ph.D degree in 2014 from Hong Kong Baptist University. Since then, he is a post-doc researcher with Prof. Licheng Sun in KTH Royal Institute of Technology, Sweden. His research interests are synthesis of new organic photovoltaic materials for solar cells application.

Jinbao Zhang is currently a Ph.D student in Physical Chemistry at Uppsala University, Sweden. His research is focus on the synthesis and characterization of conducting polymer and small-molecule based hole transporting materials for solid-state dye sensitized solar cells and perovskite solar cells. He studied physical electrochemistry at Central South University (2006–2010) for a bachelor degree; and studied applied electrochemistry in the field of lithium ion batteries (2010–2012) for a master degree.

Bo Xu obtained his Ph.D degree under the supervision of Prof. Licheng Sun at the Center of Molecular Devices, Organic Chemistry, KTH Royal Institute of Technology, Sweden, in 2015. He is currently a postdoctoral in KTH Royal Institute of Technology. His research mainly focuses on the development of organic hole transport materials (HTMs) and p-type dopants for solid-state dye-sensitized solar cells (ssDSCs) and perovskite solar cells (PSCs).

Peng Liu is currently a Ph.D. student in Applied Physical Chemistry at the Royal Institute of Technology in Sweden. His research is focusing on fundamental study on efficient solid-state dye sensitized solar cells and perovskite solar cells. Recently he is mainly working on the characterization of organic dye molecules and hole transport materials for efficient solid state photovoltaic. His research interests also embrace fundamental aspect of photo-catalysis and computational material science.

Ming Cheng received his Ph.D. in 2014 from Dalian University of Technology (DUT). He is now working as a post-doc in KTH Royal Institute of Technology with Prof. Dr Licheng Sun. His research interest focuses on developing novel materials for new generation of solar cells including dye sensitized solar cells, organic solar cells and perovskite solar cells.

Kári Sveinbjörnsson received his M.Sc. degree in Physical Chemistry from Uppsala University in Sweden (2013). Prior to that, he received his B.Sc. degree in Chemistry, with specialization in physical and analytical chemistry, from the University of Iceland (2011). He joined Professor Anders Hagfeldt's and Professor Gerrit Boschloo's group in Uppsala University (2013) and is currently, under the supervision of Assistant Professor Erik M. J. Johansson, working towards a doctoral degree in physical chemistry. His main research focus is on perovskite solar cells.

Kerttu Aitola obtained her Ph.D in Aalto University, Finland, in 2012, under the supervision of Professor Peter Lund. She then moved to work as a postdoctoral researcher in KTH – Royal Institute of Technology, Sweden, with Professor Lars Kloo (2012) and later Uppsala University, Sweden, with Professor Anders Hagfeldt and Professor Gerrit Boschloo (2013). Her research interests involve perovskite solar cells and dye solar cells and their alternative materials and manufacturing methods.

Erik Johansson received his Ph.D degree in Physics at Uppsala University in 2006. After postdoctoral work at Lund University he was assistant professor at Uppsala University. He is currently associate professor in Physical Chemistry at Uppsala University. His research field is nanostructured solar cells including perovskite, dye-sensitized and quantum dot solar cells. His research is spanning from understanding the fundamental processes and structure in these solar cells to the function of the full devices.

Gerrit Boschloo received his Ph.D degree in 1996 at Delft University of Technology, the Netherlands. He is currently associate professor in physical chemistry at Uppsala University, Sweden. His research is focused on fundamental research on dye-sensitized solar cells and perovskite solar cells. He has authored and coauthored over 160 peer-reviewed articles in leading journals.

Lars Kloo is since 1998 full professor in Inorganic Chemistry at Applied Physical Chemistry, KTH Royal Institute of Technology. His research has involved both experimental and theoretical studies of coordination chemistry, clusters, low-dimensional materials and ionic liquids. Since about 15 years the main research activities are devoted to liquid and solid state dye-sensitized solar cells and hybrid solar cells.

Licheng Sun received his Ph.D in 1990 from Dalian University of Technology (DUT). After a postdoc stay at Max-Planck-Institut für Strahlenchemie with Dr Helmut Görner, and as Alexander von Humboldt fellow at Freie Universität Berlin with Prof. Dr Harry Kurreck, he moved to KTH Royal Institute of Technology, Stockholm in 1995 and became assistant professor in 1997, associate professor in 1999 (Stockholm University) and full professor in 2004 (KTH). He is presently also a distinguished professor in DUT. He has published over 400 papers with >20000 citations in the fields of artificial photosynthesis, dye sensitized and perovskite solar cells.

Corresponding author at: Organic Chemistry, Center of Molecular Devices, Department of Chemistry, Chemical Science and Engineering, KTH Royal Institute of Technology, 10044 Stockholm, Sweden.

© 2016 Elsevier Ltd. All rights reserved.

Citing articles ( )

Comparing spiro-OMeTAD and P3HT hole conductors in efficient solid state dye-sensitized solar cells

Physical Chemistry Chemical Physics 2012-01-14

Comparing spiro-OMeTAD and P3HT hole conductors in efficient solid state dye-sensitized solar cells.

Lei Yang, Ute B Cappel, Eva L Unger, Martin Karlsson, Karl Martin Karlsson, Erik Gabrielsson, Licheng Sun, Gerrit Boschloo, Anders Hagfeldt, Erik M J Johansson

Abstract

Two hole conductor materials, spiro-OMeTAD and P3HT, were compared in solid-state dye-sensitized solar cells. Two organic dyes containing one anchor unit (D35) or two anchor units (M3) were used in the comparison. Absorbed photon to current conversion efficiency close to unity was obtained for the devices with spiro-OMeTAD. Energy conversion efficiencies of 4.7% and 4.9% were measured for the devices with spiro-OMeTAD and the dyes D35 and M3, respectively. For the devices using the P3HT hole conductor the results were rather different comparing the two dye molecules, with energy conversion efficiencies of 3.2% and 0.5% for D35 and M3, respectively. Photo-induced absorption measurements suggest that the regeneration of the dyes, and the polymer infiltration, is not complete using P3HT, while spiro-OMeTAD regenerates the dyes efficiently. However, the TiO(2)/D35/P3HT system shows rather high energy conversion efficiency and electrochemical oxidation of the dyes on TiO(2) indicates that D35 have a more efficient dye to dye hole conduction than M3, which thereby might explain the higher performance. The dye hole conduction may therefore be of significant importance for optimizing the energy conversion in such hybrid TiO(2)/dye/polymer systems.

Related Materials

Spiro ometad synthesis essay

Special Issue "Synthetic Metals"

Deadline for manuscript submissions: closed (29 February 2016)

Special Issue Editor

Guest Editor
Dr. Bruno Schmaltz
Laboratoire de Physico-Chimie des Matériaux et des Electrolytes pour l'Energie (PCM2E), EA 6699, UFR Sciences et Techniques, Parc de Grandmont, 37200 TOURS, France
Interests: organic semiconductors; polymer synthesis; synthetic organic chemistry; molecular designing; electronic materials; hybrid solar cells; thermoelectricity; electrochromic material; supercapacitors

Special Issue Information

Dear Colleages, In present-day society, how could we live without our cellphone, tablet, or TV set? The discovery of doped polyacetylene in 1976, and the Nobel Prize awarded to A. Heeger, A. Mc Diarmid, and H. Shirakawa in 2000 showed the wide possibilities of the use of these semiconductors. These molecules or macromolecules, which have chemical structures of alternating single and double bonds, can be considered as synthetic metals. Their specific properties, such as charge carrier mobility or thermal or electrical conductivity, are now used in a wide range of applications. One of the most interesting families of applications is “plastic electronics”, which is the gathering together of new technologies dealing with light, flexible, and cheap electronics. Even if organic semiconductors, small molecules, or polymers, are already part of commercially available technologies, such as organic light emitting diodes, organic thin film transistors, or organic photovoltaic devices, there are still challenges that need to be faced. The development of these synthetic metals as active material, include their design, their synthesis, their deposition techniques, their nanoscale organization in order to fine-tune electronic, thermal, or mechanical properties, and their performances in devices. The aim of this Special Issue is to provide the most recent advances in the fundamental chemistry and the development of new organic semiconductors for “plastic electronic” applications. Papers and review articles dealing with organic pi-conjugated materials are invited for this Special Issue on “synthetic metals”. Dr. Bruno SchmaltzGuest Editor

Keywords

organic semiconductors pi-conjugated materials electronic devices energy conversion energy storage charge transport morphology nanomaterials functional materials hybrid materials charge transfer nanocomposites

Published Papers (6 papers)

Advanced Energy Materials - Wiley Online Library

Advanced Energy Materials

Phase Separation of Li2 S/S at Nanoscale during Electrochemical Lithiation of the Solid-State Lithium–Sulfur Battery Using In Situ TEM

Zhenzhong Yang, Zhiyong Zhu, Jie Ma, Dongdong Xiao, Xian Kui, Yuan Yao, Richeng Yu, Xiao Wei, Lin Gu, Yong-Sheng Hu, Hong Li and Xixiang Zhang

Version of Record online: 26 JUL 2016 | DOI: 10.1002/aenm.201600806

S/Li2 S phase separation at nanoscale is observed for the first time in the solid-state Li–S battery by using in situ transmission electron microscopy. This nanophase separation not only reduces the diffusion distance but also provides the S/Li2 S interfaces network, which is favorable for electron and Li + ion transportation during the lithiation process.

Somayeh Gholipour, Juan-Pablo Correa-Baena, Konrad Domanski, Taisuke Matsui, Ludmilla Steier, Fabrizio Giordano, Fariba Tajabadi, Wolfgang Tress, Michael Saliba, Antonio Abate, Abdollah Morteza Ali, Nima Taghavinia, Michael Grätzel and Anders Hagfeldt

Version of Record online: 26 JUL 2016 | DOI: 10.1002/aenm.201601116

A low-cost carbon cloth is applied in perovskite solar cells (PSC) as a collector composite and degradation inhibitor. This study incorporates carbon fibers as a back contact in perovskite solar cells, which results in enhancement in all photovoltaic parameters. This material is suitable for large-scale fabrication of PSCs as it has shown an improved long-term stability when compared to the gold counterpart under elevated temperatures.

Xiaoyan Zhang, Lili Hou, Artur Ciesielski and Paolo Samorì

Version of Record online: 25 JUL 2016 | DOI: 10.1002/aenm.201600671

Graphene analogues (GAs) with remarkable electrochemical properties show great potential in energy-related applications. Here, an overview of current research and important advances on the development of 2D materials beyond graphene for supercapacitors and batteries is provided. The major challenges to be tackled, and more generally the future directions in the field, are also highlighted.

Zhonghong Xia, Li An, Peikai Chen and Dingguo Xia

Version of Record online: 25 JUL 2016 | DOI: 10.1002/aenm.201600458

Recent progress on oxygen reduction reaction (ORR) electrocatalysts used in proton-exchange-membrane fuel cells (PEMFCs) is presented, including monometallic catalysts, bimetallic or multimetallic catalysts, transition metal oxides, chalcogenides, nitrides, oxynitrides and carbides, heteroatom-doped carbon materials with and without transition metals, and metal–organic frameworks (MOFs)-derived catalysts. Key factors are demonstrated to improve ORR catalytic activities.

Yao Liu, Lawrence A. Renna, Zachariah A. Page, Hilary B. Thompson, Paul Y. Kim, Michael D. Barnes, Todd Emrick, Dhandapani Venkataraman and Thomas P. Russell

Version of Record online: 25 JUL 2016 | DOI: 10.1002/aenm.201600664

Poly(Phenylene vinylene) anionic polyelectrolyte (PVBT-SO3 ) was found to be an efficient hole extraction layer for inverted perovskite solar cells. It can be cast from an aqueous solution and does not require thermal annealing for improved device performance. The devices show maximum solar cell efficiency of 15.9% and exhibit improved stability under ambient conditions and enhanced charge extraction.

Modular design of SPIRO-OMeTAD analogues as hole transport materials in solar cells - Chemical Communications (RSC Publishing) DOI

Modular design of SPIRO-OMeTAD analogues as hole transport materials in solar cells†

Alexander T. Murray‡. Jarvist M. Frost‡. Christopher H. Hendon‡. Christopher D. Molloy. David R. Carbery and Aron Walsh *
Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK. E-mail: a.walsh@bath.ac.uk

Received 12th March 2015. Accepted 23rd April 2015

First published on the web 23rd April 2015

We predict the ionisation potentials of the hole-conducting material SPIRO-OMeTAD and twelve methoxy isomers and polymethoxy derivatives. Based on electronic and economic factors, we identify the optimal compounds for application as p-type hole-selective contacts in hybrid halide perovskite solar cells.

Considerable scientific effort has been focused on the challenge of converting sunlight to electricity. Recently, solution-processed hybrid perovskite based solar cells have reached power conversion efficiencies of 20.1%, values competitive with the mature silicon technologies. 1–10 A critical component of any solar cell (or optoelectronic device) is the electrical contact, which needs to efficiently and selectively extract electrons or holes from the active layer. In order to maximise the photovoltage and photocurrent, the energy levels of the contacts should be well-matched to the active layer of the device. 11 As new hybrid perovskites and alternative absorber layers are being developed for solar cells, beyond the widely employed CH3 NH3 PbI3 . the ability to modulate the energy levels of the selective contacts to match those of the absorber 12 will be essential in order to maximise power conversion efficiency.

Most high-efficiency hybrid perovskite solar cells use the hole conductor N 2. N 2. N 2 ′, N 2 ′, N 7. N 7. N 7 ′, N 7 ′-octakis(4-methoxyphenyl)-9,9′-spirobi[9 H -fluorene]-2,2′,7,7′-tetramine (SPIRO-OMeTAD, Fig. 1a ). 14,15 SPIRO-OMeTAD is widely used in solution processed solar cells with an ionisation potential well matched to a number of active (light absorbing) layers. The material forms an amorphous glass, rather than a partially crystalline phase, enabling smooth films to be formed. 16

Fig. 1 Calculated p. p -SPIRO-OMeTAD highest-occupied molecular orbital (HOMO) (a) and the associated one electron oxidised spin density (c) and p. m -SPIRO-OMeTAD HOMO (b) and the associated one electron oxidised spin density (d). The plots were made with a HOMO isovalue = 0.03 e Å −3 and spin-density isovalue = 0.01 e Å −3 in the code VESTA. 13

Electronic energy level alignment is important for solar cells, but is commonly used in post-rationalisation of successful architectures rather than as a design principle a priori. One compelling example was recently presented by Seok and co-workers, where the energy levels of SPIRO-OMeTAD were tuned by altering the connectivity of the methoxy ethers on the amino phenyl motifs. 17 Similarly, other groups are interested in the computational design of contacts for more mature photovoltaic technologies.

From the study of Seok, it was concluded that the geminal ortho -methoxyphenyl, para -methoxyphenyl arrangement produced a cell with +2% boost in conversion efficiency relative the typical SPIRO-OMeTAD (geminal para -methoxyphenyl, para -methoxyphenyl). They also found that the geminal meta -methoxyphenyl, para -methoxyphenyl isomer was detrimental to hole conduction. This increase in efficiency was correlated with an increase in oxidation potential as estimated from cyclic voltammetry, which has limited accuracy. Careful measurements using techniques such as differential pulse voltammetry (which allows for low concentration voltammetry measurements, avoiding aggregation) would allow more accurate and informative measurements with the broadly the same experimental setup. 18 Variation in device-to-device performance, and issues such as implicit doping 19 from various syntheses of hybrid or organic electronic materials, means that it requires extremely large study to provide the definitive answer of which material is optimal.

In solar cells, SPIRO-OMeTAD can be used in the neutral, one and two electron oxidised forms. Chemical doping with lithium salts is typically performed to increase conductivity. 20 Fig. 1 shows the Kohn–Sham highest occupied molecular orbital (HOMO) of the neutral, and the singly-occupied molecular orbital (SOMO) of the cationic radical state of the most common SPIRO-OMeTAD isomer ( p. p -SPIRO-OMeTAD), as well as the p. m isomer previously found to be detrimental. These frontier orbitals provide a qualitative interpretation of the chemical bonding. Both the HOMO and SOMO show similar electronic structure: the electron density is centred on the extended π network, primarily on the carbons.

The oxidised doublet state can be viewed as the removal of an electron from this π system; the associated spin density is centred again on the carbon system, but there is significant spin stabilisation from the heteroatoms ( i.e. N). Additionally, the amino phenyl carbons, as defined by the position of the methoxy ether motifs, do not appear to affect the contribution to the delocalised radical. This effect is notable as the amino phenyl motifs are not part of the extended π system due to the violation of Hückel planarity. 21

Due to the lack of π planarity, we would not expect organic modifications to affect the ionisation potential to the extent we observe for typical planar conjugated systems. 22 This suggests that isomer modifications should allow for energy level modulation, within a narrow range, through repositioning of the methoxy ether motifs. 23,24

To investigate the possible synthetic scope in modifying the side chains, we have predicted the energy level alignment of p. p -SPIRO-OMeTAD and 12 structurally related isomers (Fig. 3 ). These calculations are by hybrid density functional theory (DFT) with atom-centered numerical basis functions (see ESI† for full details). We report both the Kohn–Sham energy gap (from B3LYP), and more reliable ionisation potentials were calculated with the delta self-consistent field (ΔSCF) method. All calculations were of a single molecule in the gas phase, as we were looking for relative variations in the ionisation potential, rather than an absolute value for the solid state, which may be influenced by molecular packing. We do not consider these values to be definitive. More accurate model chemistries might achieve more precise gas phase values, but the variation caused by solid state packing in the real system would have more of an effect on device performance and the overall accuracy of such predictions.

As detailed in Fig. 2. we defined the two aminoaryl rings as r1 and r2 . and used o. m. and p to refer to regiochemistry relative to the amine (or bromide). These correspond to the 2-, 3- and 4-positions, respectively. The predicted electronic modulation is modest, but important in the context of efficient hole extraction. Two important conclusions can be made: (i) meta -methoxy substitutions result in generally increased ionisation potentials, as the contribution of the oxygen donation is reduced with reduced structural symmetry (lowering the energy of the π system); (ii) para - and ortho -substituted derivatives result in decreased ionisation potentials due to the increased energy of the π system. In the cases of poly-OMe substitutions, the decreased ionisation potential is also realised by the repulsive interaction between neighbouring rings.

Fig. 3 The calculated single-particle Kohn–Sham energy gaps ( E g ) and ΔSCF ionisational potentials (IP) for a range of SPIRO-OMeTAD derivatives (as defined in Fig. 2 ). The black dashed horizontal line refers to the IP of p. p -SPIRO-OMeTAD.

The Kohn–Sham energy gap ( E g . written in colour in Fig. 3 ) is relatively constant for all isomers. Here, the HOMO eigenvalue deviates from our ΔSCF ionisation potential, suggesting that Koopman's approximation is insufficient for predicting even qualitative trends. However, our ΔSCF calculations are in close agreement with the experimentally determined ionisation potential for the p. p -analogue, 25 and with the p. m -analogue, 17 though we contradict experiment and predict that the p. o -analogue 17 should see an enhancement.

An especially interesting molecule is the case in which r1 = r2 = o. o. This derivative has a notably smaller ionisation potential than other analogues, which is likely due to both the electron donating contribution of the ortho -positions and ‘through-space’ conjugation to the amine motif. 26

Tuning the energy levels in a contact material is only a partial fulfilment of the requirements – we also need to transport the holes efficiently, and so avoid surface recombination. Calculating charge carrier transport for a novel organic material is extremely difficult, as a full model of packing and an understanding of the dielectric environment is required before microscopic charge transfer integrals can be calculated and a macroscopic mobility predicted. 27 One expects that adding bulky side chains would decrease the molecular packing density and coordination number, and so reduce the electronic overlap and thus microscopic mobility.

A barrier to the large-scale production of novel solar cells is the cost of SPIRO-OMeTAD. This can be partially attributed to the recent fluctuations in supply and demand, but is also due to the cost of the starting materials. A typical synthesis of SPIRO-OMeTAD begins with the Pd-catalysed coupling of anisidine ( para -methoxyaniline) and para -methoxybromobenzene to form a secondary aniline. Four equivalents of the aniline are then resubjected to similar coupling conditions with the brominated spiro core; 2,2′,7,7′-tetrabromo-9,9′-spirobi[9 H -fluorene], Fig. 2. forming p. p -SPIRO-OMeTAD. 17 In principle, any commercially available aniline and aryl bromide could be used to construct a diverse library of electronically dissimilar SPIRO-OMeTAD derivatives. Assuming isomer transferable reaction conditions ( i.e. the use of the same catalysts, purification methods and yields) we have included a rudimentary cost break down associated with the reagents required for our library (see ESI† for a full cost analysis).

Beyond the cases considered here, greater electronic variability should be achievable through substitution about the fluorene core (direct conjugation modulation). However, given the current lack of commercial availability of alternate core materials, this could be a more synthetically challenging endeavour. Recent advances in aryl C–H activation chemistry could find a useful application in the functionalisation of these molecules. 28–31

In conclusion, we have calculated the ionisation potentials of a variety of analogues of the hole conducting material SPIRO-OMeTAD, varying the HOMO energy through alterations to the positioning of methoxy groups on the pendant aryl rings of the molecule. Our method is computationally efficient, has been shown to offer good agreement with experimental measures from solution voltammetry. We predict that these synthetic variants offer flexibility in work function matching for solar cell design and optimisation, and that the majority of analogues could be candidates for large-scale development and application.

We thank K. Tobias Butler for lyrical insights. We acknowledge membership of the U.K.'s HPC Materials Chemistry Consortium, which is funded by EPSRC Grant EP/L000202. Additional support has been received from EPSRC Grants EP/K016288/1 and EP/J017361/1, the Royal Society, and the ERC (Grant no. 277757).

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Footnotes

† Electronic supplementary information (ESI) available: Full cost analysis and computational methods. See DOI: 10.1039/c5cc02129d

Spiro ometad synthesis essay

Spiro-OMeTAD (also called Spiro-MeOTAD) Key References

[1] Interface engineering of highly efficient perovskite solar cells . Huanping Zhou et al., Science, V 34, p.546 (2014).

Key details: High efficiency perovskite solar cells with >19% efficiency. Doping regime specified via reference [2].

[2] Sequential deposition as a route to high-performance perovskite-sensitized solar cells . Julian Burschka et al., Nature, V499 p.316 (2013).

Key details: Spin coated spiro-MeOTAD in chlorobenzene doped with the below compounds (doping ratio's specified in reference [3]:

[3] Nanostructured TiO2 /CH3 NH3 PbI3 heterojunction solar cells employing spiro-OMeTAD/Co-complex as hole-transporting material . Jun Hong Noh et al., J. Mater. Chem. A, 1, 11842-11847, DOI: 10.1039/C3TA12681A (2013)

Key details: Doped with the below concentrations

  • 50 mM spiro-OMeTAD in chlorobenzene
  • Co( III )-complex (FK209) first dissolved into an acetonitrile stock solution prepared with concentrations in the range 4 to 33 mM before being added to the Spiro/chlorobenzene solution.
  • FK209 stock solution mixed with Spiro/chlorobenzene solution to give overall 7.7 mol% FK209 to Spiro.
  • Also doped with a stock solution of Li-bis(trifluoromethanesulfonyl)imide (Li-TFSI) at 170 mg and TBP at 46.6% by volume in acetonitrile.
  • Spin-coated at 3000 rpm for 30s.

To the best of our knowledge the technical information provided here is accurate. However, Ossila assume no liability for the accuracy of this information. The values provided here are typical at the time of manufacture and may vary over time and from batch to batch.

New iridium complex as additive to the spiro-OMeTAD in perovskite solar cells with enhanced stability

Abstract

A new iridium complex, IrCp*Cl(PyPyz)[TFSI], has been synthesized and used as additive for the hole transporter material, spiro-OMeTAD, in perovskite solar cells. The cells prepared with this Ir additive present higher efficiency than reference cells, and similar to cells prepared with Co additive. We have determined that the presence of metal complexes as additives decreases the recombination rate, as it has been observed by impedance spectroscopy. Very interestingly, while the efficiency after 3 months decreases by 22% and 70% for reference cell and cell with Co additive, respectively, the efficiency of devices containing the Ir additive is only decreased by a 4%.

© 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

The work was supported by MINECO of Spain under project MAT2013-47192-C3-1-R, Universitat Jaume I project 12I361.01/1. E.M.-M. thanks the Ramón y Cajal program. R.S.S. thanks the FP7 European project ALLOXIDE (309018).

Abstract

A new iridium complex, IrCp*Cl(PyPyz)[TFSI], has been synthesized and used as additive for the hole transporter material, spiro-OMeTAD, in perovskite solar cells. The cells prepared with this Ir additive present higher efficiency than reference cells, and similar to cells prepared with Co additive. We have determined that the presence of metal complexes as additives decreases the recombination rate, as it has been observed by impedance spectroscopy. Very interestingly, while the efficiency after 3 months decreases by 22% and 70% for reference cell and cell with Co additive, respectively, the efficiency of devices containing the Ir additive is only decreased by a 4%.

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New iridium complex as additive to the spiro-OMeTAD in perovskite solar cells with enhanced stability