The Hagfeldt Donor and Use of Next‐Generation Bulky Donor Designs in Dye‐Sensitized Solar Cells

Abstract

“The Hagfeldt donor” is a bulky triarylamine building block with four alkyl chains in a 3‐dimensional arrangement that is used with organic dyes in dye‐sensitized solar cells (DSCs) in over 140 publications. Many of the highest performing DSC devices in literature make use of this group due to exceptional TiO2 surface protection properties, which slows recombination of electrons in TiO2 with the electrolyte. Importantly, record‐setting cobalt and copper redox shuttle‐based DSCs require exceptional surface protection to slow a facile recombination of electrons to these positively charged redox shuttles. Several syntheses have emerged for the Hagfeldt donor due to the need for iterative aryl–halide cross‐ coupling reactions complicating a straightforward route. Six synthetic strategies found in literature are described along with the challenges of each route. A recent method that has been put forward in the literature as a scalable, regioisomerically pure route is highlighted.

Synthetic Efforts to Investigate the Effect of Planarizing the Triarylamine Geometry in Dyes for Dye-Sensitized Solar Cells

“…This suggests that this geometry in fact produces a superior surface passivation compared to the triarylamine dyes. As the triarylamine class of dyes has gained much of its success from being superb blockers of electron recombination, 21 the improved blocking ability of 10 H -PTZ-Fu is an impressive feature of this dye. The surface passivation properties of the 3,7-phenothiazine dye were also comparable to that of the triarylamine dyes.…”

“… 3 , 5 , 17 − 20 The triarylamine scaffold holds a three-dimensional propeller shape that provides an umbrella effect for the surface of TiO 2 , where it prevents the electrolyte from approaching the semiconductor and recombining with the electrons there. 21 …”

Toward Sustainable, Colorless, and Transparent Photovoltaics: State of the Art and Perspectives for the Development of Selective Near‐Infrared Dye‐Sensitized Solar Cells

“…One approach consists of adding the bulky triarylamine building block with four alkyl chains known as "The Hagfeldt donor." [38] There is a great variety of NIR dyes that have been synthesized for DSSC. [39] Nevertheless, to reach selective NIR-DSSC, the dye requires an absorption close to zero in the whole spectral region covered by the human cones.…”

Indoor light-harvesting dye-sensitized solar cells surpassing 30% efficiency without co-sensitizers

“…In general, metal-free organic dyes adopt <> bridgeacceptor $*<>< % design enabling superior charge separation, higher molar extinction coefficient, ease of bandgap engineering and better photostability. [38][39][40][41] Diphenylamines, triarylamines, carbazoles, porphyrins and indoles were used as potential organic sensitizers, of which carbazoles occupy a prominent position due to its high electron-donating capability and improved photo and thermal stability. 29,35,[48][49][50][51][52][53]36,39,[42][43][44][45][46][47] DSCs fabricated with one of the well-studied commercial and efficient carbazole dye MK 2, having regioregular n-hexyl substituted quater-thiophene and cyanoacrylic acid resulted in 8.3% power conversion efficiency under 1 sun condition.…”