Alcohol-Soluble n-Type Conjugated Polyelectrolyte as Electron Transport Layer for Polymer Solar Cells

摘要

A novel alcohol-soluble n-type conjugated polyelectrolyte (n-CPE) poly-2,5-bis(2-octyldodecyl)-3,6-bis(thiophen-2-yl)-pyrrolo [3,4-c]pyrrole-1,4-dione-alt-2,5-bis[6-(N,N,N-trimethyl-ammonium)hexyl]-3,6-bis(thiophen-2-yl)-pyrrolo[3,4-dpyrrole-1,4-dione (PDPPNBr) is synthesized for applications as an electron transport layer (ETL) in an inverted polymer solar cells (PSCs) device. Because of the electron-deficient nature of diketopyrrolopyrrole (DPP) backbone and its planar structure, PDPPNBr is endowed with high conductivity and electron mobility. The interfacial dipole moment created by n-CPE PDPPNBr can substantially reduce the work function of ITO and induce a better energy alignment in the device, facilitating electron extraction and decreasing exctions recombination at active layer/cathode interface. As a result, the power conversion efficiency (PCE) of the inverted devices based poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C-61 butyric acid methyl ester (PC61BM) active layer with PDPPNBr as ETL achieves a value of 4.03%, with 25% improvement than that of the control device with ZnO ETL. Moreover, the universal PDPPNBr ETL also delivers a notable PCE of 8.02% in the devices based on polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7):(6,6)-phenyl-C-71-butyric acid methyl ester (PC71BM). To our best knowledge, this is the first time that n-type conjugated polyelectrolyte-based cathode interlayer is reported. Quite different from the traditional p-type conjugated and nonconjugated polyelectrolytes ETLs, n-CPE PDPPNBr as ETL could function efficiently with a thickness approximate 30 nm because of the high conductivity and electron mobility. Furthermore, the PDPPNBr interlayer also can ensure the device with the improved long-term stability. The successful application of this alcohol solution processed n-type conjugated polyelectrolyte indicates that the electron-deficient planar structure with high electron mobility could be very promising in developing high performance and environmentally friendly polymer solar cells.