Photovoltaic Performance Improvement of P3HT:PCBM Polymer Solar Cells by Annealing Treatment

Several polymer solar cells consisting of ITO/PEDOT: PSS/P3HT: PCBM/Al (indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester/aluminum cathode) were fabricated by spin coating. The influence of annealing temperature on the performance of the polymer solar cells was studied using absorption spectra, photoluminescence spectra, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). These devices were treated at 120 degrees C for 10 min in an ambient atmosphere and the best power conversion efficiency (PCE) of 2.00% was obtained at an open circuit voltage (V-oc) of 0.64 V, a short circuit current density (J(sc)) of 10.25 mA . cm(-2), and a fill factor (FF) of 38.1%. The intensities of the absorption peaks at 560 and 610 nm increased because of the increased absorption pi ->pi* transition of P3HT after annealing treatment. XRD spectra showed that the intensity of the diffraction peaks at (100) for P3HT increased 1.8 times by comparison with that of the cells that did not undergo annealing treatment. The P3HT:PCBM phase separation increased markedly after annealing treatment, which is valuable for exciton dissociation. FTIR results also showed that the polymer materials did not deteriorate during the annealing treatment process.