Diminishing of S-shaped J-V curves by substrate heating in organic solar cells based on triplet materials

Abstract

ABSTRACT The S-shaped J-V curves in planar heterojunction organic solar cells (OSCs) using triplet material bis[2-(4-tertbutylphenyl)benzothi azolato-N , C 2 ,] iridium (acetylacetonate) [(t-bt) 2 Ir(acac)] as donor and C 60 as acceptor were diminished by substrate heating during film deposition of (t-bt) 2 Ir(acac) layer. Mobility meas urements showed that the disappearance of S-kinks was attributed to the significant increase of hole mobility in (t-bt) 2 Ir(acac) by heating the substrate during evaporation and thus the decrease of mobility mismatch between electrons and holes, leading to the improvement of fill factor ( FF ). Moreover, the photocurrent density ( J ph ) of heated device was remarkable enhanced and showed decreased space charge limited (SCL) effect due to the balanced charge transport and the increase of charge collection efficiency (  CC ). As a result, by heating the substrate at 70  , a power conversion efficiency ( PCE ) of 1.63 % was achieved compared to 1.37 % for the unheated device. Using this method, organic solar cells based on triplet materials allow thicker active layer thickness for light absorption without introducing much fill factor loss. Keywords: Organic solar cells (OSCs), substrate heating, S-kinks, triplet materials