Surface engineering of the electron collecting layers for high performance organic photovoltaic cells

Abstract

Surface engineering of the electron collecting layers (ECLs) is a straightforward and practical strategy to develop high performance inverted structure organic solar cells (OSCs). Here, we systematically investigate four different types of surface modified ECLs to implement high performance low-energy band gap poly[4,8-bis[(2-ethylhexyl) oxy] benzo[1,2-b: 4,5-bA] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b]-thiophenediyl] (PTB7) and [6,6]-phenyl-C-70-butyric acid methyl ester (PC70BM) based inverted OSCs: (1) single PEIE, (2) ZnO: PEIE mixture (1: 1 vol ratio), (3) PEIE/ZnO bilayer, and (4) ZnO/PEIE bilayer. OSCs with the ZnO/PEIE ECL show the highest power conversion efficiency (PCE) value of 8.61% while all the other devices exhibit PCE values of less than 7.80%. The excellent surface coverage as well as proper band alignment of the ZnO/PEIE bilayer leads to the highest device performance. (C) 2017 Elsevier B.V. All rights reserved.