| Polymer solar cell (PSC) is considered as the cheap and high quality substitution of silicon-based solar cells, because of its significant advantage of various kinds of materials, light, flexible, processable, and can be filmed in large areas, designed in molecules. However, there are defects in the lower energy conversion efficiency. We carry out the following researches around the polymer bulk heterojunction solar cells.Firstly, the paper elaborates photoelectric conversion mechanism of five kinds of PSC with different structures in detail, and summarizes some effective ways to improve energy conversion efficiency (η) of PSC.Secondly, in Matlab/Simulink the paper creates several simulation models which is based on the analysis of equivalent circuit and IV characteristic of PSC, it simulates output characteristics of photovoltaic cells in different light intensity, series resistance (Rs), shunt resistance (Rsh), and we gain a result that device performance characteristics which is close to the actual device. We draw the conclusions from simulations: First, solar cell is a nonlinear device, which output is closely related to many variables, such as temperature, light intensity, Rs and Rsh. Secend, light intensity directly affects output power (P0) of solar cells, as light intensity increasing, P0, Isc and Voc increase. Third, Rs and Rsh have great impact on IV characteristic of device. As the decrease in Rs, device's Isc, Fill Factor (FF) and conversion efficiency increase significantly. As the increase in Rsh, device's Voc enhance. It also shows that device's Voc is mainly affected by Rsh, nothing to do with Rs. Rsh has no effect on the Isc, while Rs has no effect on Voc. Lower Rs and higher Rsh can result in a sound FF, and the energy conversion efficiency of device will increase.Finally, 7 groups were prepared for measurement and characterization in our experiments. Preparation of different heat treatment devices and comparison of morphology, IV and PV characteristic curve, we obtain effects of Voc, Isc, FF andηon device with different heat treatments. In ITO / PEDOT:PSS / PCBM:P3HT / Al, annealing takes active layer absorption spectrum red shift. At the meant time, it increases roughness and crystallinity of active layer, so that phase separation of P3HT and PCBM occurs, which is helpful for carrier to transfer in the interpenetrating network and also improves carrier mobility of organic semiconductors to some extent. Post-annealled not only changes phase separation in active layer, but also changes state of contact surface between active layer and metal electrode probably. The relative uneven surface in active layer may increase contact areas between active layer and Al, which is more helpful for carrier to be absorpted and extracted by electrode. After annealing device's Rs greatly reduce, while surface roughness increase, which largely reduces light reflection so as to improve Isc, Voc and FF. We measure IV characteristic of three groups that dealed with different heat treatments, and find that pre-annealled device's Voc, Jsc, FF was 0.421V, 1.53mA/cm2, 30.79%, increase by 71.8%, 30.8%, 26.2% compared with unannealled, andηincrease from 0.08% to 0.21%. By comparision, post-annealled device's Jsc promotes from 1.53mA/cm2 to 5.03mA/cm2,ηincreases nearly 3 times from 0.21% to 0.77%, although its Voc increase not much, even FF appeares to decline slightly. |
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