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.