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Strategy to Boost the Efficiency of Mixed-Ion Perovskite Solar Cells: Changing Geometry of the Hole Transporting Material.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
KTH Royal Inst Technol, Ctr Mol Devices, Dept Chem Chem Sci & Engn, Organ Chem, SE-10044 Stockholm, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
Ecole Polytech Fed Lausanne, Inst Chem Sci & Engn, Lab Photomol Sci, EPFL FSB ISIC LSPM, Chemin Alambics,Stn 6, CH-1015 Lausanne, Switzerland.
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2016 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 10, no 7, 6816-6825 p.Article in journal (Refereed) Published
Abstract [en]

The hole transporting material (HTM) is an essential component in perovskite solar cells (PSCs) for efficient extraction and collection of the photoinduced charges. Triphenylamine- and carbazole-based derivatives have extensively been explored as alternative and economical HTMs for PSCs. However, the improvement of their power conversion efficiency (PCE), as well as further investigation of the relationship between the chemical structure of the HTMs and the photovoltaic performance, is imperatively needed. In this respect, a simple carbazole-based HTM X25 was designed on the basis of a reference HTM, triphenylamine-based X2, by simply linking two neighboring phenyl groups in a triphenylamine unit through a carbon-carbon single bond. It was found that a lowered highest occupied molecular orbital (HOMO) energy level was obtained for X25 compared to that of X2. Besides, the carbazole moiety in X25 improved the molecular planarity as well as conductivity property in comparison with the triphenylamine unit in X2. Utilizing the HTM X25 in a solar cell with mixed-ion perovskite [HC(NH2)2]0.85(CH3NH3)0.15Pb(I0.85Br0.15)3, a highest reported PCE of 17.4% at 1 sun (18.9% under 0.46 sun) for carbazole-based HTM in PSCs was achieved, in comparison of a PCE of 14.7% for triphenylamine-based HTM X2. From the steady-state photoluminescence and transient photocurrent/photovoltage measurements, we conclude that (1) the lowered HOMO level for X25 compared to X2 favored a higher open-circuit voltage (Voc) in PSCs; (2) a more uniform formation of X25 capping layer than X2 on the surface of perovskite resulted in more efficient hole transport and charge extraction in the devices. In addition, the long-term stability of PSCs with X25 is significantly enhanced compared to X2 due to its good uniformity of HTM layer and thus complete coverage on the perovskite. The results provide important information to further develop simple and efficient small molecular HTMs applied in solar cells.

Place, publisher, year, edition, pages
2016. Vol. 10, no 7, 6816-6825 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-300728DOI: 10.1021/acsnano.6b02442ISI: 000380576600046PubMedID: 27304078OAI: oai:DiVA.org:uu-300728DiVA: diva2:952234
Funder
Swedish Energy AgencyStandUpSwedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Research Council Formas
Available from: 2016-08-12 Created: 2016-08-11 Last updated: 2016-09-14Bibliographically approved
In thesis
1. Organic Hole Transport Materials for Solid-State Dye-Sensitized and Perovskite Solar Cells
Open this publication in new window or tab >>Organic Hole Transport Materials for Solid-State Dye-Sensitized and Perovskite Solar Cells
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solid-state dye-sensitized solar cells (ssDSSCs) and recently developed perovskite solar cells (PSCs) have attracted a great attention in the scientific field of photovoltaics due to their low cost, absence of solvent, simple fabrication and promising power conversion efficiency (PCE). In these types of solar cell, the dye molecule or the perovskite can harvest the light on the basis of electron excitation. Afterwards, the electron and hole are collected at the charge transport materials.

Photoelectrochemical polymerization (PEP) is employed in this thesis to synthesize conducting polymer hole transport materials (HTMs) for ssDSSCs. We have for the first time developed aqueous PEP in comparison with the conventional organic PEP with acetonitrile as solvent. This water-based PEP could potentially provide a low-cost, environmental-friendly method for efficient deposition of polymer HTM for ssDSSCs. In addition, new and simple precursors have been tested with PEP method. The effects of dye molecules on the PEP were also systematically studied, and we found that (a) the bulky structure of dye is of key importance for blocking the interfacial charge recombination; and (b) the matching of the energy levels between the dye and the precursor plays a key role in determining the kinetics of the PEP process.

In PSCs, the HTM layer is crucial for efficient charge collection and its long term stability. We have studied different series of new molecular HTMs in order to understand fundamentally the influence of alkyl chains, molecular energy levels, and molecular geometry of the HTM on the photovoltaic performance. We have identified several important factors of the HTMs for efficient PSCs, including high uniformity of the HTM capping layer, perovskite-HTM energy level matching, good HTM solubility, and high conductivity. These factors affect interfacial hole injection, hole transport, and charge recombination in PSCs. By systematical optimization, a promising PCE of 19.8% has been achieved by employing a new HTM H11. We believe that this work could provide important guidance for the future development of new and efficient HTMs for PSCs.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 83 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1408
Keyword
photoelectrochemical polymerization, PEDOT, dye, hole transport material, small molecule, perovskite solar cell
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-300802 (URN)978-91-554-9659-3 (ISBN)
Public defence
2016-10-07, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Available from: 2016-09-15 Created: 2016-08-14 Last updated: 2016-09-22

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