Boron Nitride/Sulfonated Polythiophene Composite Electrocatalyst as the TCO and Pt-Free Counter Electrode for Dye-Sensitized Solar Cells: 21% at Dim Light

Boron nitride (BN) is newly introduced as a nonmetal electro-catalyst for the counter electrode of a dye-sensitized solar cell (DSSC). By applying a conductive binder of sulfonated poly(thiophene-3-[2-(2-methoxyethoxy)ethoxy]-2,5-diyl) (s-PT), the BN/s-PT composite film was successfully wrapped around each carbon fiber (CF) in the flexible carbon cloth (CC) substrate via a low-cost drop-coating method. Each CF in the CC provided a one-dimensional electron transfer core, and the wrapped BN/s-PT composite film functioned as the mesoporous electro-catalytic shell. Compared to pristine BN and pristine s-PT electrodes, the electrochemical and impedance performances of the BN/s-PT composite film were incredibly enhanced because of the synergetic effect of the BN nanoparticle and the s-PT binder; the former offered a large active surface area and a high intrinsic heterogeneous rate constant, and the latter formed fast electron transfer matrices. With a proper BN weight percentage among BN/s-PT solutions, the best DSSC coupling with a BN/s-PT composite counter electrode exhibited a good cell efficiency (η) of 9.21% at 1 sun, showing a great potential to substitute the expensive platinum (8.11%). At the dim light environment (i.e., T5 fluorescent illumination), the DSSC reached attractive η′s of 21.02% (6000 lux), 19.52% (3000 lux), and 17.48% (1000 lux).