a)The values in the bracket are integrated from EQE spectrum; b)Measured by space charge limited current (SCLC) method.
To further understand the exciton dissociation process of the binary and ternary devices, the photocurrent density (J ph) versus effective applied voltage (V eff) was measured (Figure 2c). J ph is calculated by the formula of J ph =J L-J D, whereJ L and J D are the photocurrent density in the light and in the dark.V eff is calculated by the formula ofV eff = V o-V .V o denotes the voltage when the theJ ph =0, and V denotes the applied voltage. All the devices obtain their saturated photocurrent density (J sat) when the V eff = 2V. The exciton dissociation probability (P diss) and charge collection efficiency (P coll) are calculated from J ph/J satand J maxpower/J sat under the short-circuit condition and maximal power output point, respectively. The specific data are displayed at Table S4. All the devices showed highP diss over 97% and P collover 81%. And the ternary device achieves the highestP diss of 98.2% and P collof 84.4%, indicating the effective exciton dissociation and charge collection processes.
The hole and electron mobilities (μ h andμ e) are measured by the space charge-limited current (SCLC) method for investigating the charge transport of the blend films (Figures 3a and 3b). As a result, theμ h / μ e values of PBDB-T: BZ4F-O-1, PBDB-T: BZO-4Cl and PBDB-T: BZ4F-O-1: BZO-4Cl based devices are 6.9×10-5/6.6×10-5, 9.0×10-5/1.51×10-4 and 3.17×10-4/4.20×10-4cm2V-1s-1, respectively (Table 2 and Table S5). The less balanced charge transport of the PBDB-T: BZO-4Cl blend leads to a poor FF of 0.64. However, the ternary blend achieves both the increased μ h /μ e values and a more balanced charge transport, therefore, the J SC and FF are simultaneously improved.