Donor group influence on dye-sensitized solar cell device performances: Balancing dye loading and donor size

Abstract

Four high photocurrent near-infrared (NIR)-absorbing metal-free organic sensitizers (ND1, ND2, ND3, and AP25) with varying nitrogen-based donor groups are examined for use in dye-sensitized solar cell (DSC) devices. One of the highest photocurrent generating organic dyes based on a triarylamine donor reported in the literature (AP25 at 19 mA/cm2) is compared to dyes varying the donor group with constant intramolecular charge transfer π-bridge-acceptor systems. Specific popular donor groups include the bulky Hagfeldt donor (ND1), a carbazole donor (ND2), and an indoline donor (ND3) which varies a large range of sizes (maximum width varies between 8 Å and 26 Å). Computational analysis, dye energetics, absorption profiles (in solution and on TiO2), device incident photon-to-current conversion efficiencies (IPCEs), electrochemical impedance spectroscopy, small modulated photovoltage transient spectroscopy, and device current-voltage curves are used to probe dye behavior based on donor group selection. Balancing donor size and dye loadings was found to be critical for higher performances with the DSC dyes accessing low energy photons near 900 nm.