Panchromatic NIR-Absorbing Sensitizers with a Thienopyrazine Auxiliary Acceptor for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) are a cost-effective and highly tunable technology for harvesting solar energy. Current research is focused on the design of near-infrared (NIR, >700 nm) absorbing organic sensitizers to efficiently harvest low-energy photons to increase the efficiency of DSCs. Herein, two NIR sensitizers containing a proaromatic thienopyrazine (TPZ) auxiliary acceptor are synthesized. The optical, electrochemical, and device properties of the sensitizers were studied. The two dyes probe the placement of the TPZ auxiliary acceptor (A′) either between the π-bridge and the acceptor (WM1, D−π–A′−A) or between the donor and the π-bridge (WM2, D–A′−π–A). WM1 and WM2 exhibit absorption maxima at 631 and 604 nm in dichloromethane (DCM), respectively. Both dyes also have higher energy absorption features, which contributes to panchromatic absorption into the NIR region. Optimized devices were sequentially sensitized with Y123 to control the surface conformation of the TPZ dyes, yielding high photocurrent values of 20.3 and 14.4 mA/cm2 for WM1 and WM2, respectively. WM1 exhibits a low-energy NIR incident photon-to-current efficiency (IPCE) onset at ∼900 nm.