| 초록 |
We designed and synthesized three conjugated polymers based on carbazole and TPD unit with 3 different thiophene spacers from thiophene , thieno[3,2-b]thiophene, bithiophene (PCTTPD, PCTTTPD, PCBTTPD abbreviated as P1, P2, P3) to fine-tune deep HOMO level (-5.72 eV, -5.67eV, -5.57eV). Increasing conjugation length from P1 to P3 resulted in up-shifted HOMO level with red-shifted absorption spectra. Polymer:PC71BM based photovoltaic cells resulted in Voc drop (from 0.94 V, 0.90 V to 0.86 V) which matches with energy offset difference of LUMOPCBM - HOMOpolymer. In turn, Jsc was enhanced from 2.70 mA/cm2, 3.86 mA/cm2 to 7.79 mA/cm2 with overall PCE improvement (1.14%, 1.25%, 3.42%). Measured residual PL spectra indicate that HOMO level of -5.67 eV suffers from efficient charge separation at the interface due to poor back hole transfer. Conjugated polymer with deep HOMO level should be carefully designed to obtain high Voc with ensuring efficient back hole transfer. |
