The effect of SrTiO3:ZnO as cathodic buffer layer for inverted polymer solar cells

Abstract

Dual phase SrTiO3:ZnO nanocomposite films with varied composition ratios were fabricated by sol–gel processing and applied as cathodic buffer layers (CBL) for inverted polymer solar cells, and demonstrated enhanced power conversion efficiency. Basic properties of SrTiO3:ZnO CBL films were examined by means of XRD, XPS, AFM, UV–vis absorption spectra, and goniometry. When the cathodic buffer layers were assembled to solar cells, the device properties including incident photon-to-current conversion efficiency (IPCE), power conversion efficiency, and electron mobility were investigated systematically. SrTiO3 in CBL was found to be amorphous or quasiamorphous. Although more detailed experiments are needed, SrTiO3 is more likely to have some local ordering structure with aligned TiO6 octohedra, i.e., quasiamorphous phase, and thus possesses spontaneous polarization as reported in the literature (Frenkel et al., 2005 [1]; Frenkel et al., 2007 [2]; Ehre et al., 2007 [3]; Ehre et al., 2007 [4]; Ehre et al., 2007 [5]). Such spontaneous polarization is likely to induce a self-built electric field to prevent electron recombination on the interface of the bulk heterojunction (BHJ) active layer and cathodic buffer layer (CBL), and result in high power conversion efficiency.