In Situ Formation of ZnO in Graphene: A Facile Way To Produce a Smooth and Highly Conductive Electron Transport Layer for Polymer Solar Cells

A novel electron transport layer (ETL) based on zinc oxide@graphene:ethyl cellulose (ZnO@G:EC) nanocomposite is prepared by in situ formation of zinc oxide (ZnO) nanocrystals in a graphene matrix to improve the performance of polymer solar cells. Liquid ultrasound exfoliation by ethyl cellulose as stabilizer not only allows for uniform dispersion of graphene solution but also maintains an original structure of graphene gaining a high conductivity. The ZnO@G:EC ETL displays a quite smooth morphology and develops the energy-level alignment for the electron extraction and transportation. Subsequently, the device based on poly­(3-hexylthiophene) (P3HT):(6,6)-phenyl-C₆₁ butyric acid methyl ester (PC₆₁BM) with the ZnO@G:EC as ETL obtains a power conversion efficiency (PCE) of 3.9%, exhibiting a ∼20% improvement compared to the familiar device with bare ZnO nanocrystals as ETL. Replacing the active layer with polythieno­[3,4-<i>b</i>]­thiophene/benzodithiophene (PTB7): (6,6)-phenyl-C₇₁ butyric acid methyl ester (PC₇₁BM), the PCE can be dramatically improved to 8.4%. This facile and fascinating method to produce a smooth and highly conductive electron transport layer provides an anticipated approach to obtain high performance polymer solar cells

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

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-<i>c</i>]­pyrrole-1,4-dione-<i>alt</i>-2,5-bis­[6-(<i>N</i>,<i>N</i>,<i>N</i>-trimethyl­ammonium)­hexyl]-3,6-bis­(thiophen-2-yl)-pyrrolo­[3,4-<i>c</i>]­pyrrole-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-C₆₁ 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-<i>b</i>]-thiophene-<i>co</i>-benzo­dithiophene (PTB7):(6,6)-phenyl-C₇₁-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