Chemical doping is an important strategy to alter the charge-transport properties of both molecular and polymeric organic semiconductors that find widespread application in organic electronic devices. We report on the use of a new class of Co(III) complexes as p-type dopants for triarylamine-based hole conductors such as spiro-MeOTAD and their application in solid-state dye-sensitized solar cells (ssDSCs). We show that the proposed compounds fulfill the requirements for this application and that the discussed strategy is promising for tuning the conductivity of spiro-MeOTAD in ssDSCs, without having to rely on the commonly employed photo-doping. By using a recently developed high molar extinction coefficient organic D-π-A sensitizer and p-doped spiro-MeOTAD as hole conductor, we achieved a record power conversion efficiency of 7.2%, measured under standard solar conditions (AM1.5G, 100 mW cm(-2)). We expect these promising new dopants to find widespread applications in organic electronics in general and photovoltaics in particular.

SummaryThe high molar extinction coefficient heteroleptic ruthenium dye, NaRu(4,4 -bis(5-(hexylthio)thiophen-2-yl)-2,2 -bipyridine) (4-carboxylic acid-4 -carboxylate-2,2 -bipyridine) (NCS) 2 , exhibits certified 5% electric power conversion efficiency at AM 1.5 solar irradiation (100 mW cm −2 ) in a solid-state dye-sensitized solar cell using 2,2 ,7,7 -tetrakis-(N,N-dipmethoxyphenylamine)-9,9 -spirobifluorene (spiro-MeOTAD) as the organic hole-transporting material. This demonstration elucidates a class of photovoltaic devices with potential for low-cost power generation. © 2010 Elsevier Ltd. All rights reserved.The dye-sensitized nanocrystalline solar cell (DSC) offers special opportunities in the realm of renewable energy sources primarily stemming from its use of low-cost mate- * Corresponding author. Fax: +86 431852 62953. rials and its lack of stringent conditions required for device manufacturing [1]. In the quest for new sensitizers leading to an enhancement of the photon-to-electron conversion efficiency, the creation of new ruthenium dyes still remains a promising option. Indeed, recent improvements in the design and synthesis of new dyes have made it possible to obtain greater than 11% light-to-energy conversion efficiencies. The majority of these newly developed sensitizers involve polypyridyl-type complexes of ruthenium [2][3][4]. Advantages in terms of improved sealing properties and long-term cell stability can be realized by replacing the liquid electrolytes utilized in DSC by a solid-state 1748-0132/$ -see front matter

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A new amphiphilic polypyridyl ruthenium complex, cis-Ru(dpbpy)(dnbpy)(NCS) 2 (dpbpy ) 4,4′-diphosphonic acid-2,2′-bipyridine; dnbpy ) 4,4′-dinonyl-2,2′-bipyridine), was synthesized and demonstrated as an efficient sensitizer. The sensitizer was characterized by NMR, voltammetry, ATR-FTIR, resonance Raman, as well as electronic absorption and emission spectra. Nanocrystalline dye-sensitized solar cells (DSCs) with this new sensitizer generated g8.0% power conversion efficiencies under illumination with simulated air mass 1.5 sunlight. This is the first time such a high solar-to-electricity power conversion efficiency for DSCs has been reached by a sensitizer bearing non-carboxylic acid anchoring groups. Additionally, the devices exhibited excellent stability under light soaking at 55 to 60°C. Time-resolved nanosecond laser experiments revealed that the dye regeneration rate of this new sensitizer seems to be quite similar but the charge recombination is significantly slower in comparison to the analogues carboxylated sensitizer.

A ruthenium sensitizer (coded C101, NaRu (4,4′‐bis(5‐hexylthiophen‐2‐yl)‐2,2′‐bipyridine) (4‐carboxylic acid‐4′‐caboxylate‐2,2′‐bipyridine) (NCS)2) containing a hexylthiophene‐conjugated bipyridyl group as an ancillary ligand is presented for use in solid‐state dye‐sensitized solar cells (SSDSCs). The high molar‐extinction coefficient of this dye is advantageous compared to the widely used Z907 dye, (NaRu (4‐carboxylic acid‐4′‐carboxylate) (4,4′‐dinonyl‐2,2′‐bipyridine) (NCS)2). In combination with an organic hole‐transporting material (spiro‐MeOTAD, 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine) 9, 9′‐spirobifluorene), the C101 sensitizer exhibits an excellent power‐conversion efficiency of 4.5% under AM 1.5 solar (100 mW cm−2) irradiation in a SSDSC. From electronic‐absorption, transient‐photovoltage‐decay, and impedance measurements it is inferred that extending the π‐conjugation of spectator ligands induces an enhanced light harvesting and retards the charge recombination, thus favoring the photovoltaic performance of a SSDSC.