Exciton blocking and dissociation by a p-type anode buffer in small molecule bulk heterojunction organic photovoltaic with small ratio donor of phosphorescent material

In this work, we demonstrated significant improvements in organic photovoltaic (OPV) cells by inserting a p-type material at anode part, which served as an exciton dissociation layer/blocking layer (EDL/BL). The EDL/BL is a neat layer that prevents exciton quenching while also provides an additional heterojunction to promote exciton dissociation. By employing bulk heterojunction (BHJ) OPV devices in which the active blend film is C-60 matrix with a low-concentration phosphorescent material, a notable 33% increase of power conversion efficiency (PCE) from 1.75% to 2.31% was achieved. Through studying different p-type materials as EDL/BL, i.e., 4,-4'-Bis(carbazol-9-yl)-biphenyl (CBP), 4,4,4-Tris(N-carbazolyl-triphenylamine) (TCTA), N, N'-dicarbazolyl-3,5-benzene (mCP) and N', N'-Di-1-naphthyl-N', N'-diphenyl-1, 1'-biphenyl-4,4'-diamine (NPB), it was found that the hole mobility of EDL/BL as well as their energy levels had a crucial effect on the performance of OPV cells. Employing CBP as EDL/BL, C-70 with wider and more intensive absorption as acceptor instead of C-60, PCE of 3.96% was obtained. (C) 2015 Elsevier B.V. All rights reserved.