Triplet excitons in a ladder-type conjugated polymer: Application in solar cells

Inclusion of trace quantities of heavy metal atoms (Pd) in a ladder-type polymer (PhLPPP) backbone allows transitions between the singlet and the triplet manifolds. Temperature-dependent photoinduced absorption studies of PhLPPP show the triplet–triplet absorption peak (T1 → TN) at 1.3 eV to blue-shift with increasing temperatures, suggesting a localization of the excitons on smaller chain segments with large exchange splitting energy. Furthermore, solar cells were fabricated using PhLPPP as the donor material; on an average the power conversion efficiencies of PhLPPP-based solar cells were 3–10 times greater compared to the ladder-type polymer with no incorporation of Pd atoms.