π-Conjugation Effects of Oligo(thienylenevinylene) Side Chains in Semiconducting Polymers on Photovoltaic Performance

Abstract

Semiconducting copolymers based on benzo-[1,2-b:4,5-b′]dithiophene and thieno [3,4-c]pyrole-4,6-dione containing oligo(thienylenevinylene) side chains with different lengths were synthesized to examine the effect of the πconjugated side chains on the performance of polymer solar cells (PSCs). Using the copolymers that had π-conjugated side chains as the PSC electron donor resulted in a higher short circuit current and fill factor compared with the reference copolymers, which had no side chain or an analogous side chain with no π-conjugation, resulting in an increase of power conversion efficiency of 10−22%. Measurements of hole mobility by space-charge-limited current and internal quantum efficiency indicated that introducing the π-conjugated side-chain units can facilitate both charge transport and charge separation in the polymer:PC 71 BM blend films.

Synthesis and characterization of highly conjugated side‐group‐substituted benzo[1,2‐b:4,5‐b′]dithiophene‐based copolymer for use in organic solar cells

“…450 nm) was attributed to the conjugated TTV side group in the BDT unit because this peak agreed well with the absorption peak of compound 6 [Fig. (a)] . The absorption band of PBDT‐TTV was slightly broader (approx.…”

“…The hole mobilities of the PBDT‐OR:PC 70 BM (1:1) and PBDT‐TTV:PC 70 BM (1:2) blend films were 2.2 × 10 −5 and 1.0 × 10 −4 cm 2 /V s, respectively, that is, the trend is similar to that in the mobilities of the pure polymer films. The mobility in the PBDT‐TTV film is higher than that in the PBDT‐OR film, which is probably due to the strong interchain interactions among the conjugated TTV side groups …”

“…Given the hole mobilities of the polymers, the PBDT‐TTV devices are expected to exhibit higher J SC values than the PBDT‐OR devices. Note that the incorporation of the conjugated TTV side groups into the BDT units, which increases the strength of the intermolecular interactions, significantly increases the absorption intensity and hole mobility, and thereby enhances the J SC and PCE values of the PBDT‐TTV solar cell devices.…”

“…BDT‐based polymers that incorporate various conjugated side chains have been widely studied and have contributed to highly efficient OPV applications . Recently, Tajima and coworkers reported the synthesis and characterization of a conjugated tris(thienylenevinylene) (TTV) group that incorporated BDT‐based conjugated terpolymers . The TTV units were introduced into the main chain between the BDT donors and various acceptor units.…”

“…The TTV units were introduced into the main chain between the BDT donors and various acceptor units. The highly conjugated TTV side chains increased the hole mobility by improving interchain charge transport to form better connections between the polymer chains . Among potential electron acceptors, thieno[3,4‐ c ]pyrrole‐4,6‐dione (TPD) is an important building blocks due to good electron delocalization in the solid state as a result of a relatively compact and planar structure …”