Co(III) Complexes as p‑Dopants in Solid-State Dye-Sensitized Solar Cells

Following our recent work on the use of Co­(III) complexes as p-type dopants for triarylamine-based organic hole-conductors, we herein report on two new Co­(III) complexes for doping applications. With the aim of ameliorating the dopant’s suitability for its use in solid-state dye-sensitized solar cells, we show how the properties of the dopant can be easily adjusted by a slight modification of the molecular structure. We prove the eligibility of the two new dopants by characterizing their optical and electrochemical properties and give evidence that both of them can be used to oxidize the molecular hole-transporter spiro-MeOTAD. Finally, we fabricate high-performance solid-state dye-sensitized solar cells using a state-of-the-art metal-free organic sensitizer in order to elucidate the influence of the type of dopant on device performance

Molecular Engineering of Organic Dyes for Improved Recombination Lifetime in Solid-State Dye-Sensitized Solar Cells

A major limitation of solid-state dye-sensitized solar cells is a short electron diffusion length, which is due to fast recombination between electrons in the TiO₂ electron-transporting layer and holes in the 2,2′,7,7′-tetrakis­(<i>N</i>,<i>N</i>-di-<i>p</i>-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) hole-transporting layer. In this report, the sensitizing dye that separates the TiO₂ from the Spiro-OMeTAD was engineered to slow recombination and increase device performance. Through the synthesis and characterization of three new organic D-π-A sensitizing dyes (WN1, WN3, and WN3.1), the quantity and placement of alkyl chains on the sensitizing dye were found to play a significant role in the suppression of recombination. In solid-state devices using Spiro-OMeTAD as the hole-transport material, these dyes achieved the following efficiencies: 4.9% for WN1, 5.9% for WN3, and 6.3% for WN3.1, compared to 6.6% achieved with Y123 as a reference dye. Of the dyes investigated in this study, WN3.1 is shown to be the most effective at suppressing recombination in solid-state dye-sensitized solar cells, using transient photovoltage and photocurrent measurements

Tris(2-(1<i>H</i>-pyrazol-1-yl)pyridine)cobalt(III) as p-Type Dopant for Organic Semiconductors and Its Application in Highly Efficient Solid-State Dye-Sensitized Solar Cells

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