Planar Perovskite Solar Cells with High Open-Circuit Voltage Containing a Supramolecular Iron Complex as Hole Transport Material Dopant

Yasemin Saygili; Silver-Hamill Turren-Cruz; Selina Olthof; Bartholomeus Wilhelmus Henricus Saes; Ilknur Bayrak Pehlivan; Michael Saliba; Klaus Meerholz; Tomas Edvinsson; Shaik M Zakeeruddin; Michael Grätzel; Juan-Pablo Correa-Baena; Anders Hagfeldt; Marina Freitag; Wolfgang Tress

doi:10.1002/cphc.201800032

Planar Perovskite Solar Cells with High Open-Circuit Voltage Containing a Supramolecular Iron Complex as Hole Transport Material Dopant

Chemphyschem. 2018 Jun 5;19(11):1363-1370. doi: 10.1002/cphc.201800032. Epub 2018 Apr 26.

Authors

Yasemin Saygili¹, Silver-Hamill Turren-Cruz^{1

2}, Selina Olthof³, Bartholomeus Wilhelmus Henricus Saes⁴, Ilknur Bayrak Pehlivan⁵, Michael Saliba⁴, Klaus Meerholz³, Tomas Edvinsson⁵, Shaik M Zakeeruddin^{1

4}, Michael Grätzel⁴, Juan-Pablo Correa-Baena^{1

6}, Anders Hagfeldt¹, Marina Freitag⁷, Wolfgang Tress¹

Affiliations

¹ Laboratory of Photomolecular Science, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, 1015, Lausanne, Switzerland.
² Benemérita Universidad Autónoma de Puebla., CIDS, Av. San Claudio y 18 Sur, Col. San Manuel, Ciudad Universitaria, CP 72570, P.O. Box 1067, Puebla, Pue., 7200, México.
³ Department of Chemistry, University of Cologne, Luxemburger Straße 116, 50939, Cologne, Germany.
⁴ Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, 1015, Lausanne, Switzerland.
⁵ Department of Engineering Sciences, Solid State Physics, Uppsala University, Box 534, SE, 751 21, Uppsala, Sweden.
⁶ Current Address: Massachusetts Institute of Technology, Cambridge, MA, USA, 02139.
⁷ Department of Chemistry- Ångström Laboratory, Uppsala University, 751 20, Uppsala, Sweden.

PMID: 29697180
DOI: 10.1002/cphc.201800032

Abstract

In perovskite solar cells (PSCs), the most commonly used hole transport material (HTM) is spiro-OMeTAD, which is typically doped by metalorganic complexes, for example, based on Co, to improve charge transport properties and thereby enhance the photovoltaic performance of the device. In this study, we report a new hemicage-structured iron complex, 1,3,5-tris(5'-methyl-2,2'-bipyridin-5-yl)ethylbenzene Fe(III)-tris(bis(trifluoromethylsulfonyl)imide), as a p-type dopant for spiro-OMeTAD. The formal redox potential of this compound was measured as 1.29 V vs. the standard hydrogen electrode, which is slightly (20 mV) more positive than that of the commercial cobalt dopant FK209. Photoelectron spectroscopy measurements confirm that the iron complex acts as an efficient p-dopant, as evidenced in an increase of the spiro-OMeTAD work function. When fabricating planar PSCs with the HTM spiro-OMeTAD doped by 5 mol % of the iron complex, a power conversion efficiency of 19.5 % (AM 1.5G, 100 mW cm^-2 ) is achieved, compared to 19.3 % for reference devices with FK209. Open circuit voltages exceeding 1.2 V at 1 sun and reaching 1.27 V at 3 suns indicate that recombination at the perovskite/HTM interface is low when employing this iron complex. This work contributes to recent endeavors to reduce recombination losses in perovskite solar cells.

Keywords: iron complex dopant; p-type HTM doping; perovskite solar cells; solar energy production.