Investigation On The Performance Improvement Of Polymer Solar Cells By Annealing And Iodine Doping

In 1986,C.W. Tang put forward the structure of the double layers organic solar cells. In 1995, Heeger proposed the concept of bulk-heterojunction solar cells. The 21st century, the power conversion efficiency of polymer solar cells increased to more than 7%. After twenty years of development, polymer solar cells (PSCs) have achieved breakthroughs in one after another. The thesis based on P3HT:PCBM bulk-heterojunction solar cells focus on the effect of annealing and doping treatments on the performance of PSCs. Get the following two conclusions:i) these devices were treated at 120℃for 10 min in an ambient atmosphere and the best power conversion efficiency (PCE) of 2.00% was obtained; ii) the distinguished enhancement of short circuit current density (Jsc) and the PCE of PSCs with 5% concentration iodine doping were obtained. Comparing annealing and iodine doping, both of them improve the performance of PSCs. Specific results are as follows:Several PSCs consisting of ITO/PEDOT:PSS/P3HT:PCBM/Al 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℃for 10 min in an ambient atmosphere and the best power conversion efficiency (PCE) of 2.00% was obtained at an open circuit voltage (Voc) of 0.64 V, Jsc of 10.25 mA/cm2, and a fill factor (FF) of 38.1%. The intensities of the absorption peaks at 560 and 610 nm increased 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.A series of poly(3-hexylthiophene) (P3HT)/(6,6)-phenyl C60 butyric acid methyl ester (PCBM) bulk hetero-junction polymer solar cells were fabricated with different iodine (I2) doping concentrations. The Jsc was increased to 8.7 mA/cm2 from 4 mA/cm2, meanwhile Voc was decreased to 0.52V from 0.63V when the iodine doping concentration is 5%. The optimized PCE of PSCs with iodine doping is about 1.51%, which should be attributed to the better charge carrier transport and collection, and the more photon harvesting due to the red shift of absorption peaks and the widened absorption range to the longer wavelength. The morphology and phase separation of polymer thin films were measured by AFM. The phase separation of P3HT and PCBM has been distinctly increased, which is beneficial to the exciton dissociation. Improve the performance of P3HT:PCBM PSCs.