Regular paper

Improvement of performance and stability of polymer photovoltaic cells by WO₃/CuPc as anode buffer layers

¹ Department of Physics, Faculty of Sciences, Shahrekord University, P.O. Box 115, Shahrekord, Iran
² Nanotechnology Research Center, Shahrekord University, 8818634141 Shahrekord, Iran

^* ghasemi.mohsen@sci.sku.ac.ir

Received: 21 April 2015
Revised: 4 May 2015

Abstract

In this work, bulk-hetrojunction polymer photovoltaic cells based on poly-(3-hexylthiophene) (P3HT): [6, 6]-phenyl C61 butyric acid methyl ester (PCBM) were fabricated with tungsten oxide (WO₃) and copper phthalocyanine (CuPc) as anodic buffer layers. The WO₃ plays an important role in reducing the interfacial resistance, efficiently extracting holes and good band structure matching between the work function of the anode and the highest occupied molecular orbital of the organic material. The insertion of CuPc improves the device performance and expands the absorption spectra range of the photovoltaic devices. The effects of WO₃ and CuPc thickness on the performance of the photovoltaic devices were investigated. The optimum thicknesses of WO₃ and CuPc were 10 nm and 8 nm, respectively. The obtained power conversion efficiency of optimized cell was about 4.21%. Also, the device performance was analyzed based on the surface roughness of bare ITO and ITO that was covered with poly (3, 4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) or WO₃/CuPc. The device stability in an ambient atmosphere without encapsulation under continuous light irradiation was also investigated. For the cell with PEDOT:PSS, the power conversion efficiency reduced down to 50% of the maximum value (half-life) after light irradiation for 12 h, while the half-life of device for WO₃/CuPc was about 120 h. Therefore, the lifetime of unpackaged devices was improved with WO₃/CuPc.