Acceptor (A) - donor (D) - acceptor (A) type conjugated small molecule based on 2,1,3-benzothiadiazole and silofluorene (2,7-bis[5-(7-methyl-benzo[1,2,5]thiadiazol-4-yl)-thiophen-2-yl]-9-(9,9-dioctyl)-9H-silofluorene, SiF-BT) is synthesized for application in organic solar cells (OSCs). Even though two thiophene rings are introduced as the π-extender, SiF-BT exhibits a wide band gap of 2.26 eV due to weak intramolecular charge transfer between SiF and BT. The HOMO and LUMO energy levels of SiF-BT figured out from the cyclic voltammogram and UV-Visible spectrum are -5.43 and -3.17 eV, respectively. Optimized OSCs with a blend of SiF-BT:PC71BM (3:6) exhibits a power conversion efficiency (PCE) of 0.53% with a short-circuit current density of -2.06 mA/cm2, fill factor of 29.8%, and open-circuit voltage of 0.90 V.

2,1,3-benzothiadiazole(BT)과 silofluorene(SiF)을 기본골격으로 하는 acceptor(A) - donor(D) - acceptor(A) 형태의 공액형(conjugated) 분자(SiF-BT)를 합성하였다. 공액결합의 길이를 늘여 주기 위하여 두 개의 thiophene을 SiF와 BT 사이에 도입하였으나 밴드갭은 꽤 큰 2.26 eV에 불과하였다. 이는 SiF와 BT 사이의 intramolecular charge transfer 의 정도가 작기 때문이라 판단된다. 순환전압전류법 및 흡수분광법을 이용하여 측정한 SiF-BT의 HOMO 및 LUMO 에너지 준위는 각각 -5.43 and -3.17 eV이며, 최적화된 유기태양전지의 효율은 0.53%(단락전류=-2.06 mA/cm2, 충진인자=29.8%, 개방전압=0.90 V)임을 확인하였다.

Keywords: conjugated oligomer; silofluorene; benzothiadiazole; organic solar cell