Application of Polyaniline Composites at Flexible Counter Electrode of Dye Sensitized Solar Cells

• Main Authors: Yu-Chuan Lan, 藍鈺荃
• Other Authors: King-Fu Lin
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/42726877800691664024

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 104 === The main idea of this thesis was to fabricate a flexible and low-cost counter electrode for liquid state dye sensitized solar cells. Three methods were applied---chemical deposition, electrochemical polymerization, and chemical-electrochemical polymerization. We used scanning electron microscopy, thermogravimetry analysis, cyclic voltammetry, four-point probe, etc. to characterize of PANi/graphite composite. We also conducted photovoltaic tests, electrochemical impedance spectroscopy, etc. to observe the device performance. For chemical deposition, we adopted a new dip coating method. Different reaction time was set, which was 1.0, 1.5, 2.0, 2.5, and 3.0 minute. Two groups---1 and 2-layered PANi on Graphite composites---were applied in DSSCs. The DSSC with counter electrode of 1-layered PANi by 1.5 minute has the best performance with power conversion efficiency (PCE) of 6.16 ± 0.229 %, short circuit current density (Jsc) of 16.1 ± 0.0777 mA/cm2, open circuit voltage (Voc) of 0.697 ± 0.0238 V, and fill factor (FF) of 0.571 ± 0.0369. For electrochemical polymerization, there are four groups---PANi, PANi/CNT, PANi/Graphen, and PANi/CNT/Graphene all on graphite substrate---prepared by different reaction time, which was 25, 50, 75, 100, and 125 second. PANi/CNT/Graphene on graphite substrateby 75 second has the highest PCE of 6.34 ± 0.122 %, with Jsc of 12.9 ± 0.0570 mA/cm2, Voc of 0.692 ± 0.0122 V, and FF of 0.674 ± 0.00470. Generally, the DSSCs with CNT or/and Graphene in PANi/Graphite substrate have improved PCE and performance. For chemical-electrochemical polymerization, 1-layered PANi by 1.5 minute was deposited on the counter electrode followed by electrochemical polymerization of PANi with different reaction time as mentioned previously. The DSSCs with PANi followed by PANi/CNT on graphite substrate by 50 second has the highest PCE of 5.35 ± 0.0981 %, with Jsc of 13.0 ± 0.0901 mA/cm2, Voc of 0.694 ± 0.0281 V, and ff of 0.574 ± 0.0185. From the decreasing Voc in I-V curves with reaction time and voltage decrease in hysteresis diagrams, we proposed the possible existence of capacity of PANi in DSSC system, which would impose large impact on the performance of DSSCs. The capacity effect might come from change of oxidation state of PANi. The electrons from external circuit would reduce the protonated emeraldine salt which is at medium oxidation state. Besides, as reaction time for PANi gets longer, the fiber structure interweaves into a network, which imposes steric hindrance for the redox couple (iodide/triiodide) in the electrolyte and thus decrease the reduction rate of triiodide. Although more surface area is created as PANi grows more complexly, the small pores of the network structure prevent redox couples from diffusing into the inside of PANi and undergoing redox reaction. Capacitance effect builds up a reverse potential to the DSSC. Under illumination, Voc and Jsc of DSSCs with PANi as the counter electrode feature a descending tendency with increasing reaction time of PANi.