Full text loading...
Molecular structures of polymers synthesized (a) P1 (y = 0) and P1a (x = 2/3, y = 1/3) and (b) P2a (x = 2/3, y = 1/3). The subunits of the terpolymers are statistically distributed. (c) Absorption of the synthesized terpolymers compared to copolymers. Copolymer P2 spectrum is taken from Ref 10.
Transient absorption of P2a:PCBM blend showing hole transfer from the chromophore unit to the triarylamine after electron transfer to PCBM. Panel (a) shows the data surface, while panel (b) shows spectra at selected times and (c) shows kinetic traces at selected wavelength ranges. The absorption bleach of the chromophore reduces as holes are transferred to the hole transport unit.
Panel (a) compares the time evolution of the normalized absorption bleach between 550 and 560 nm of P1 and P1a after a 510 nm excitation pulse. While the bleach of P1 stays roughly constant (slight increase and decrease due to spectral diffusion followed by recombination), the bleach of P1a decreases to 4/9 of its initial value within 500 ps as all the holes generated on chromophores neighboring a hole transport unit (HTU) transfer. Panel (b) illustrates that the probability of an excited chromophore having at least one directly adjacent HTU is 5/9.
Normalized decay of the photoinduced charge absorption after 1, 5, and 10 μJ/cm2, 532 nm excitation, respectively (black, red, and blue lines) for (a) P1, (b) P1a, and (c) P2a. In P1, the rate of charge recombination is density dependent, indicating that free charges were generated. In P1a and P2a, the charge recombination rate does not depend on density. In conjunction with pulsed LED transient current measurements, this indicates that most likely trap-assisted recombination is dominant in the terpolymers.
Performance of organic solar cells with co- and terpolymers as donor materials mixed with PCBM in a 1:2 ratio (3:7 for P2). Data for copolymer P2 are taken from the literature. See Ref. 10.
Article metrics loading...