Planar heterojunction organic photovoltaic cells based on tetramethyl substituted copper(II) phthalocyanine treated with thermal annealing

Abstract

© 2014 IOP Publishing Ltd. The fabrication of planar heterojunction (PHJ) organic photovoltaic (OPV) cells using tetramethyl substituted copper(II) phthalocyanine (CuMePc) as an electron donor and C60as an acceptor is described. The impact of post-fabrication thermal annealing upon the performance of these cells has been examined. Atomic force microscopy (AFM) images and UV-visible absorption spectra of CuMePc thin films revealed crystallization of CuMePc induced by thermal annealing at 190°C. The crystallized CuMePc films accounted for improved hole mobility, broadened absorption spectrum, and increased donor/acceptor interface in the as-fabricated cells after thermal annealing. AFM images also revealed that the surface of MoO3film was smooth and close-packed after thermal annealing, which efficiently blocked the leakage current in the annealed cells, leading to dramatic improvement of performance for the PHJ cells using CuMePc as the electron donor and MoO3or V2O5as the anode buffer layer. The power conversion efficiency of the thermal-annealed PHJ cell with a configuration of ITO/MoO3/CuMePc/C60/Bathocuproine/Al was higher than that of the bulk heterojunction (BHJ) cell fabricated by co-depositing CuMePc and C60. It was mainly because the isolated clusters of CuMePc and/or C60molecules formed during the fabrication of the BHJ cell was avoided in the PHJ cell.