Bulky 3D Structures of Dithienopyrrol Dye with Copper(II/I) Redox Mediator Enabling Efficient Solar Cells with an Open-Circuit Voltage of 1.13 V

Abstract

Efficiently suppressing on interface recombination of dye-sensitized solar cells (DSCs) enables high open-circuit photovoltage (Voc) through exploiting photosensitizers. Herein, a dithienopyrrol derivative photosensitizer C260A featuring a bulky auxiliary donor N-(2′,4′-bis(hexyloxy)-[1,1′-biphenyl]-4-yl)-2′,4′-bis(hexyloxy)-N-methyl-[1,1′-biphenyl]-4-amine (BP-DPA) and a traditional electron-acceptor cyanoacrylic acid (CA) was reported. Dye C260A with a bulky auxiliary donor moiety in the DSC outperforms the reference dye C260 with the state-of-the-art donor bis(4-(hexyloxy)phenyl)amine (DPA). Although the substitution of bulky auxiliary donor hardly alters the optical energy gap, C260A possesses prolonged equilibrium excited-state lifetimes in both dye-diluted solution and dye-grafted alumina film than the C260-based counterpart. These two photosensitizers are used to make coadsorbate-free, high-photovoltage-output DSCs in combination with a Cu(II/I) redox mediator. Electric and photophysical measurements show that the C260A-based DSC endows a higher charge collection efficiency and a lower charge recombination rate with the copper electrolyte than the C260-based counterpart. DSC with the bulky auxiliary donor-based photosensitizer C260A achieves a high open-circuit photovoltage of 1.13 V, yielding a good power conversion efficiency (PCE) of 10.3% at 100 mW cm–2, simulated AM1.5G conditions. The cosensitization of C260A with the perylene dye C272 obtains an efficient DSC with an impressive PCE of 11.0%.