Figure 3 (a) JV characteristics, (b) EQE responses, (c) J phV eff, (d) J scP light, (e) TPC, and (f) TPV measurements of the optimized OSCs based on PM6:Tz-H and PM6:Tz-Cl .
To further understand the charge recombination and extraction processes, transient photocurrent (TPC) and transient photovoltage (TPV) measurements were carried out. As presented in Figure 3e, the charge sweep-out times under the short-circuit condition were roughly estimated to be 0.97 and 0.84 μs, while the charge carrier lifetimes obtained from the decay traces of TPV measurements (Figure 3f) were 1.59 and 1.83 μs for Tz-H - and Tz-Cl -based devices, respectively. The shorter charge extraction time can be attributed to the higher electron mobility, and the relatively longer lifetime of free carriers at open-circuit voltage may indicate less recombination in the Tz-Cl -based device.
Film morphology
To evaluate the miscibility between the two NFREAs and PM6, Flory-Huggins interaction parameters (χ ) were estimated by using contact angle measurements. The contact angles of two liquids (deionized water and ethylene glycol) on the neat PM6, Tz-H , andTz-Cl films were investigated (Figure 4a). The surface tensions (γ ) of PM6, Tz-H , and Tz-Cl were calculated to be 19.75, 26.02, and 23.90 mN m−1, respectively (Table S4). According to the empirical equation\(\chi\ =\ K(\sqrt{\gamma_{D}}-\sqrt{\gamma_{A}})^{2}\), whereK is a constant, the χ PM6:Tz-H and χ PM6:Tz-Cl were 0.43 and 0.19K , respectively, indicating a better D/A miscibility for the PM6:Tz-Cl blend film.