Dipole Formation at Active Materials/P(NDI3N-T-Br) Interface in Organic-Based Photovoltaic

In this work, a new potential electron transport material, poly[(N,N'-bis(3-(N,N-dimethyl)-N-ethylammonium)propyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-2,5-thiophene)]dibromide P(NDI3N-T-Br), is studied in conjunction with active layers formed by poly[2,3-bis(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (N2200). The energy levels of the active layer TQ1 and N2200 in contact with P(NDI3N-T-Br) have been determined by photoelectron spectroscopy. The dipole formed at the interface of the active layer and P(NDI3N-T-Br) is significantly different to the dipole formed at the respective interface with ITO. The dipole between the active layer and P(NDI3N-T-Br) blocks the transfer of holes from TQ1 to P(NDI3N-T-Br) which is desired, but the hole still transfers from the N2200 to P(NDI3N-T-Br) due to N2200 being an electron acceptor. This energy level alignment meets the expectation of using P(NDI3N-T-Br) as an interface layer in blocking the hole transfer to the interface layer when TQ1:N2200 is used in the active layer. The present work provides an understanding of P(NDI3N-T-Br) as charge extraction layer and indicates its potential to be used in organic photovoltaics.