Preparation And Properties Of Polyaniline Electrolyte And Counter Electrode For DSSCs

Dye sensitized solar cells (DSSCs) has a great practical significance to solve the energy shortage problem and develop new energy materials. However, the use of conventional liquid electrolyte in DSSCs owing to the disadvantages of fluidity and volatility results in the leakage of electrolyte, which limits the long-term performance of devices. In addition, the traditional counter electrode is composed of a platinum thin film formed on a transparent conductive glass substrate, which is relatively expensive and frangible. Considering these problems, the preparation of conducting polyaniline (PANI) used as a solid electrolyte and counter electrode for DSSCs was studied in this work. Then, the morphology, molecule structure and conductive properties of PANI were characterized respectively by Scanning Electron Microscopy, Fourier Transform Infrared spectroscopy, and four probe instrument. The growth rate of PANI synthesized on different substrate materials, and the effect of PANI morphology on the performance of the counter electrode were also analyzed. Finally, the growth mechanism of polyaniline film was preliminarily discussed. The main results are as follows:(1) A conductive polyaniline solid electrolyte was in-situ synthesized on the surface of sensitized TiO₂ anode by means of chemical oxidation polymerization. Then the photoelectrical property of solid DSSC with this PANI electrolyte was also measured. The results showed that PANI film with the best conductivity and doping effect was synthesized at 0℃for 2 hours with camphor sulfonic acid doping. Moreover, the DSSC using PANI solid electrolyte had an ideal open-circuit voltage, and 33% photo-electric conversion efficiency of the liquid DSSC. The PANI electrolyte was fully filled in TiO₂ anode, which can improve the interface contact between the electrolyte and photo anode.(2) A new PANI/acetylene black composite was fabricated as a solid electrolyte in order to enhance the interface contact between the electrolyte and counter electrode. The results showed that the incorporation of acetylene black into the polymer electrolyte improved the photovoltaic behavior of solid-state DSSC significantly, owing to the increase of the hole mobility of PANI electrolyte, the improvement of the wetting quality of the composite electrolyte, and the reinforcement of interface contact between both electrodes and the electrolyte. Finally, the DSSC with PANI-50wt% acetylene black electrolyte had 47% of the overall energy conversion efficiency of liquid DSSC. Therefore, the PANI-acetylene black composition provides one new approach for the preparation of solid electrolyte.(3) PANI counter electrodes were synthetized by potentiostatic technique on the surface of ITO conductive glasses, conductive PET, and stainless steel (SS) substrate, respectively. The results showed that the optimum processing parameters of PANI film electrodeposited on these substrates were at 1.0V for 500s, and the PANI formed a compact layer on the substrate, obtaining the highest conductivity and electrocatalytic activity. As the polymerization potential and time increasing, PANI gradually formed a loose film with the large particles or one dimension nanorods, and the conductivity and photoelectric property of PANI counter electrode were significantly decreased.(4) Owing to the intrinsic diversity of substrates, the growth rate of PANI and the contact resistance on the interface of substrates were different, which had an effect on the energy conversion efficiencies of DSSCs. The PANI flexible counter electrode with a good transparence was prepared on conductive PET plastic substrate. However, owing to the large resistance of PET substrate, the conversion efficiency of DSSC was low, which was 78% efficiency of traditional Pt electrode. And the PANI counter electrode based on the SS substrate with the advantages of low material cost, excellent flexibility and low resistance, not only reduced greatly the production cost, but also increased the efficiency of DSSC. The photoelectric measure results indicated the efficiency of DSSC with PANI/SS electrode reached 6.08%, which was higher than that with Pt electrode (4.51%). Therefore, the PANI/SS counter electrode will be a potential substitute for platinized electrode to develop a low cost, flexible counter electrode of DSSC in the future.