A new anodic buffer layer material for non-mixed planar heterojunction chloroboron subphthalocyanine organic photovoltaic achieving 96% internal quantum efficiency Chi-Feng Lin 1,a,n , Shun-Wei Liu b,n , Chih-Chien Lee c , Takeaki Sakurai d,e , Masato Kubota f , Wei-Cheng Su g , Jia-Cing Huang c , Tien-Lung Chiu h , Hsieh-Cheng Han i , Li-Chyong Chen j , Chin-Ti Chen k,n , Jiun-Haw Lee l,n a Department of Electro-Optical Engineering, National United University, Miaoli 36003, Taiwan, ROC b Department of Electronic Engineering, Ming Chi University of Technology, New Taipei City 24301, Taiwan, ROC c Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 10617, Taiwan, ROC d Institute of Applied Physics, University of Tsukuba, Tennodai 1-1-1, Tsukuba, Ibaraki 305-8573, Japan e PRESTO-JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan f Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan g Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei 10617, Taiwan, ROC h Department of Photonics Engineering, Yuan Ze University, Taoyuan 32003, Taiwan, ROC i Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan, ROC j Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan, ROC k Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan, ROC l Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan, ROC article info Article history: Received 9 June 2014 Received in revised form 15 December 2014 Accepted 10 January 2015 Keywords: Organic photovoltaic Planer heterojunction Anodic buffer layer Internal quantum efficiency abstract Nonmixed planar heterojunction (PHJ) small-molecule organic photovoltaics (OPVs) with 96% internal quantum efficiency (at 595 nm) and 4.77% power conversion efficiency (PCE) have been demonstrated. In addition to boron subphthalocyanine chloride (SubPc) and C 60 as electron donor and acceptor materials, respectively, PHJ OPVs contain an ultrathin (2 nm) buffer layer of bis-(naphthylphenylaminophenyl) fumaronitrile (NPAFN) between the indium tin oxide (ITO) anode and the donor layer (SubPc). Compared with copper phthalocyanine (CuPc) or α-naphthylphenylbiphenyl diamine (NPB) buffer layers, the NPAFN buffer layer blocks the exciton diffusion from the SubPc electron donor layer to the ITO anode more effectively and considerably improves the short circuit current (J SC ) from 5.96 (without an NPAFN layer) to 7.70 mA/cm 2 (with a 4-mm-thick NPAFN layer ). In addition, experimental results indicated that the NPAFN buffer layer reduces the crystallization, or stacking, of the SubPc electron donor, thereby limiting the reverse saturation current and elevating the open circuit voltage (V OC ) from 1.01 (without an NPAFN layer) to 1.08 V (with a-2-nm thick NPAFN layer). However, series resistance (R S ) of the OPV monotonically increases with increasing NPAFN layer thickness. The performance of the OPV is optimized when the NPAFN buffer layer thickness is 2 nm. Compared with a SubPc–C 60 PHJ OPV without an NPAFN buffer layer, the PCE of a OPV with a buffer layer increases by 22% from 3.96% to 4.77%, with a concurrent increase in J SC (from 5.96 to 7.02 mA/cm 2 ) and V OC (from 1.01 to 1.08 V). However, a decrease in R S (from 10.21 to 14.95 Ω cm 2 ) and in fill factor (from 65% to 63%) is also observed. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Organic photovoltaic (OPV) devices have been extensively studied because of their enormous potential and simple fabrication process [1–4]. In polymeric systems, a power conversion efficiency (PCE) of more than 9% has been achieved through the optimization of materials used in polymer-based bulk heterojunction (BHJ) inverted and/or tandem structures [5–8]. However, their low reproducibility and complicated purification procedure hamper their commercial appli- cation [9]. Compared with polymer BHJ solar cells, a multilayer planar heterojunction (PHJ) device fabricated using small molecules through a vacuum process suffer from a low photocurrent and short circuit current (J SC ), mainly because of the limited exciton Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells http://dx.doi.org/10.1016/j.solmat.2015.01.011 0927-0248/& 2015 Elsevier B.V. All rights reserved. n Corresponding authors. E-mail address: chifenglin@nuu.edu.tw (C.-F. Lin). 1 Tel.: þ886 37 381 722; fax: þ886 37 351 575. Solar Energy Materials & Solar Cells 137 (2015) 138–145