Effects Of Solvent Treatment On The Performances Of Polymer Solar Cells

In this work, the solvent treatment effect of P3HT/PCBM based polymer solar cells is reported. As a lowcost organic solvent, acetone is used to soak active layers for different durations. In this way, we successfully controlled the vertical distribution of the donor and the acceptor and obtained the device with high fill factor and efficiency. The measurements reveal that the interpenetrating networks and the vertical phase separation within the active layer can be significantly improved by combining the acetone treatment with the thermal annealing. The main results and conclusions in this work are as follows:1. We studied the effects of acetone treatment on the P3HT:PCBM blend films. By comparing the changes of different film color and Ultraviolet-Visible Absorption Spectrum (UV-VIS) with and without the solvent treatment, we found acetone could gradually dissolve PCBM, while the acetone treatment does not affect P3HT. Therefore the proportion of PCBM in the active layer keeps droping with the soaking time.2. We studied the effects of the acetone treatment on the morphology of P3HT.PCBM blend films. The Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) images indicate that the phase separation within the active layer in both horizontal and vertical directions are improved, resulting in a more ideal morphology of the active layer.3. We studied the acetone treatment effect on the performances of P3HT:PCBM devices with varying the weight ratios of the donor and acceptor. By controlling the acetone treatment duration and the proportion of the donor and acceptor in the active layer, we found that the device performance would improve observably when the mass ratio of the donor and acceptor is1:0.8, the acetone treating time is15s and the thermal annealing is performed. We finally acquired high quality device with the open circuit voltage of0.65V, the fill factor of63.7%, and the power conversion efficiency of3.57%.4. The reason why the acetone treatment could improve the performances of device was also investigated. By using several measurements such as UV-VIS, External Quantum Efficiency (EQE) and XPS, we found that the device with the acetone treatment does not show any improvement on photoabsorption and quantum efficiency. So the enhanced performance of the device could be mainly attributed to the optimization of the vertical phase separation and the interpenetrating networks in the active layer.