Synthesis and Characterization of Benzothiadiazole and Dicyanovinylindandione Based Small-Molecular Conjugated Materials and their Photovoltaic Properties

Abstract

A series of non-fullerene small molecules (BT-T-IDC, BT-T-tB-IDC, and BT-T-CMCN) with the architecture of A1-π-A2-π-A1 (acceptor 1-π-acceptor 2-π-acceptor 1), electron-deficient benzothiadiazole (BT) used as the core (A2), electron-rich thiophene used as the π-bridge (π), and electron-deficient dicyanovinylindandione (IDC), t-butyl substituted IDC, and dicyanomethylene-4H-chromene (CMCN) (A1) used as end groups, have been synthesized. Materials showed good thermal stability with the onset decomposition temperature (Td) upon 310 °C at 5 wt % loss for BT-T-IDC and BT-T-tB-IDC, while 304 °C at 5 wt % loss for BT-T-CMCN. BT-T-tB-IDC showed better solubility in chloroform and chlorobenzene than that of BT-T-IDC due to t-butyl groups on the IDC. The HOMO/LUMO energy levels of BT-T-IDC, BT-T-tB-IDC, and BT-T-CMCN were -5.60/-3.90, -5.71/-3.87, and -5.29 eV/-3.58 eV, respectively. Organic solar cell based on PBDBT-T (poly[(2,6-(4,8-bis (5-(2-ethylhexyl) thiophen-2-yl)-benzo [1,2-b:4,5-b’] dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis (2-ethylhexyl) benzo [1’,2’-c:4’,5’-c’] dithiophene-4,8-dione))])) as the donor and BT-T-IDC as the acceptor showed low power conversion efficiency (PCE) of 0.06% due to poor solubility. However, the PCE of the device based on BT-T-tB-IDC showed a better PCE of 1.55%. On the other hand, the device based on BT-T-CMCN was employed as the donor unit and PC71BM as the acceptor unit. The best performance based on BT-T-CMCN/PC71BM in inverted-type of organic solar cells (OSCs) exhibits the PCE of 0.69%.

A1-π-A2-π-A1 (acceptor 1-π-acceptor 2-π-acceptor 1) 구조의 비-풀러렌(Non-Fullerene) 저분자 (BT-T-IDC, BT-T-tB-IDC, BT-T-CMCN)를 합성하였다. 여기서, dicyanovinylindandione (IDC), t-butyl substituted IDC, dicyanomethylene-4H-chromene (CMCN)는 말단(A1)으로, benzothiadiazole (BT)는 중심(A2)으로, 전자가 풍부한 thiophene 은 π-bridge (π)로 사용되었다. BT-T-IDC 및 BT-T-tB-IDC는 310 ℃에서 5wt % 손실 열분해 온도 (Td)로 좋은 열 안정성을 보였고, BT-T-CMCN은 304 ℃로 마찬가지로 좋은 열 안정성을 나타냈다. BT-T-tB-IDC는 t-butyl 기로 인하여 BT-T-IDC보다 클로로포름 및 클로로벤젠에서 우수한 용해도를 보였다. BT-T-IDC, BT-T-tB-IDC 및 BT-T-CMCN의 Highest Occupied Molecular Orbital (HOMO) / Lowest Unoccupied Molecular Orbital (LUMO) 에너지 준위는 각각 -5.60eV / -3.90eV, -5.71eV / -3.87eV, -5.29eV / -3.58eV이었다. PBDB-T (poly[(2,6-(4,8-bis (5-(2-ethylhexyl) thiophen-2-yl)-benzo [1,2-b:4,5-b’] dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis (2-ethylhexyl) benzo [1’,2’-c:4’,5’-c’] dithiophene-4,8-dione))])) (Donor)와 BT-T-IDC (acceptor)는 낮은 용해도로 인해 0.06 %의 낮은 전력 변환 효율 (PCE)을 보였다. 그러나 BT-T-tB-IDC를 acceptor 로 적용한 태양전지의 효율은 개선된 용해도의 영향으로 1.55 %로 개선되었다. 한편, BT-T-CMCN는 Donor로, PC71BM((6,6)-Phenyl-C71 butyric acid methyl ester)은 acceptor로 사용되었고, 그 효율은 0.69 %로 나타났다.