| Description |
We measured resonant Raman scattering (RRS) and doping-induced absorption (DIA) in pristine films of π-conjugated donor-acceptor (D-A) copolymers, as well as the photoinduced absorption (PIA) spectra of their blend with fullerene PCBM molecules. We found that dominant charge carriers in these copolymers are polaron excitations. In addition, we also found that the D-A copolymer chains contain strongly coupled vibrational modes having relatively strong Raman scattering intensity. The lower energy-induced polaron absorption band overlaps with the renormalized vibrational modes; they appear as antiresonance lines in both PIA and DIA spectra. We show that the RRS, DIA, and PIA spectra of PTB7 (fluorinated poly-thienothiophene-benzodithiophene) are well explained by the amplitude mode model. We also studied magnetic field effect in (D-A) type TADF compounds based organic light emitting diodes (OLED). Magneto-electroluminescence (MEL) and magnetophotoluminescence (MPL) in thin films of these compounds are enhanced thermally, and the response is interpreted as due to the Δg mechanism. TADF-based OLED doped with fluorescent emitters with various concentrations were also investigated. We found that both MEL and MPL responses are thermally activated with substantially lower activation energy compared to the pristine D-A TADF host blend. However, both MPL and MEL steeply decrease with the emitter's concentration indicating the existence of a loss mechanism in iv the OLED device associated with energy transfer directly into the nonemissive triplet level of the emitter. Using optical spectroscopies such as electroabsorption (EA) and PIA, we studied the primary (excitons) and long-lived (free carriers) photoexcitations in thin films of 2D lead perovskite, namely (C6H5C2H4NH3)2PbI4, which form natural "multiple quantum wells" having strong spin-orbit coupling that may lead to "Rashba-splitting" in the electron bands. From the EA spectrum, we found that the exciton binding energy is 190 meV for the 1s exciton, whereas the continuum shows Franz-Keldysh oscillation that unambiguously reveals the band-edge energy. We found a strong PIA band at 0.15 eV that is due to long-lived free carrier absorption, caused by the Rashba-splitting in this material. We obtained a Rashba-splitting energy of (40 ± 5) meV and Rashba parameter of (1.6 ± 0.1) eV·Å in this compound. |
