Synthesis and characterization of poly(N-alkyloxyarylcarbazolyl-2,7-vinylene) derivatives and their applications in bulk-heterojunction solar cells

The novel π-conjugated polymers, poly(N-(3,4-bis(decyloxy)phenyl)carbazolyl-2,7-vinylene) (PCzV) and poly[N-(3,4-bis(decyloxy)phenyl)carbazolyl-2,7-vinylene)-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene}] (PCzV-co-MEH-PPV) were synthesized by using the Gilch polymerization method and their photovoltaic properties were investigated. The newly designed and highly branched polymers, formed from PCzV and PCzV-co-MEH-PPV, are soluble in common organic solvents and easily spin-coated onto indium-tin oxide (ITO) coated glass substrates.The weight-average molecular weights (Mw) and the polydispersity of the polymers were determined to be in the ranges of 3.86–7.9 × 104 and 1.60–2.05, respectively. Bulk-heterojunction solar cells, with ITO/PEDOT:PSS/polymer:PC61BM/TiOx/Al configurations, were fabricated. The solar cell based on PCzV-co-MEH-PPV:PC61BM (1:6 wt/wt) displays a higher photovoltaic performance as compared to that produced from PCzV:PC61BM (1:6 wt/wt). The bulk-heterojunction solar cell with PCzV-co-MEH-PPV:PC61BM (1:6 wt/wt) has a power conversion efficiency (PCE) of 2.31% (Jsc = 6.43 mA/cm2, Voc = 0.82 V, FF = 44%), measured using an AM 1.5 G solar simulator at 100 mW/cm2 light illumination.