An electron beam evaporated TiO2 layer for high efficiency planar perovskite solar cells on flexible polyethylene terephthalate substrates - Qiu, W; Paetzold, UW; Gehlhaar, R; Smirnov, V; Boyen, H-G; Tait, JG; Conings, B; Zhang, W; Nielsen, CB; McCulloch, I; Froyen, L; Heremans, P; et al. (JOURNAL OF MATERIALS CHEMISTRY A, 2015)