The Performance‐Determining Role of Lewis Bases in Dye‐Sensitized Solar Cells Employing Copper‐Bisphenanthroline Redox Mediators. Issue 37 (2nd September 2020)

• Record Type: Journal Article
• Authors: Fürer, Sebastian O.; Milhuisen, Rebecca A.; Kashif, Muhammad K.; Raga, Sonia R.; Acharya, Shravan S.; Forsyth, Craig; Liu, Maning; Frazer, Laszlo; Duffy, Noel W.; Ohlin, C. André; Funston, Alison M.; Tachibana, Yasuhiro; Bach, Udo
• Is Part Of: Advanced energy materials. Volume 10:Issue 37(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-02
• Subjects: 4‐tert‐butylpyridine -- coordination -- copper electrolyte -- dye‐sensitized solar cells -- Lewis bases; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.202002067
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract: Copper redox mediators have enabled open‐circuit voltages ( V OC ) of over 1.0 V in dye‐sensitized solar cells (DSCs) and have helped to establish DSCs as the most promising solar cell technology in low‐light conditions. The addition of additives such as 4‐ tert ‐butylpyridine (tBP) to these electrolytes has helped in achieving high solar cell performances. However, emerging evidence suggests that tBP coordinates to the Cu(II) species and limits the performance of these electrolytes. To date, the implications of this coordination are poorly understood. Here, the importance of Lewis base additives for the successful implementation of copper complexes as redox mediators in DSCs is demonstrated. Two redox couples, [Cu(dmp)2 ] +/2+ and [Cu(dpp)2 ] +/2+ (with dmp = 2, 9‐dimethyl‐1, 10‐phenanthroline and dpp = 2, 9‐diphenyl‐1, 10‐phenanthroline) in combination with three different Lewis bases, TFMP (4‐(trifluoromethyl)pyridine), tBP, and NMBI (1‐methyl‐benzimidazole), are considered. Through single‐crystal X‐ray diffraction analysis, absorption, and 1 H‐NMR spectroscopies, the coordination of Lewis bases to the Cu(II) centers are studied. This coordination efficiently suppresses recombination losses and is crucial for high performing solar cells. If, however, the coordination involves a ligand exchange, as is the case for [Cu(dpp)2 ] +/2+, the redox mediator regeneration at the counter electrode is significantly retarded and the solar cells show current limitations. Abstract : The addition of Lewis bases to Cu(I/II)‐based electrolytes is crucial to achieve high‐performance dye‐sensitized solar cells. In this article, various Lewis base–electrolyte interactions and their impacts on charge transfer processes are thoroughly investigated. This study highlights Cu(II)‐Lewis base coordination—rather than ligand dissociation—as key consideration for further advancement of Cu(I/II) electrolyte‐based dye‐sensitized solar cells.