Since their introduction in 1991 [1], dye-sensitized solar cells (DSCs) have attracted considerable attention because of their high power conversion efficiency, low production cost, environmental friendliness, and high efficiency under weak ambient light [2, 3, 4]. The counter electrode (CE) is responsible for the power conversion of DSCs. The CE collects electrons from an external circuit, and catalyzes the reduction of tri-iodide to iodide, within the electrolyte. Pt [5], non-Pt catalysts including metal carbides, metal oxides, metal nitrides, metal sulfides [6, 8, 9, 10, 11], carbon materials [12] and composite materials [7, 13, 14, 15] have been investigated as CEs for DSCs.
Non-Pt catalysts for DSCs are currently a very active research area, but their application is limited by their low stability. Pt CEs are still widely used because of their high catalytic activity and stability. Different methods of preparing DSC CEs to reduce Pt usage and simplify fabrication have been widely investigated. These include magnetron sputtering [16, 17], chemical reduction [18], electro-deposition [19, 20] to two-step dip-coating [21, 22, 23] and spin-coating [24]. Sputtering requires ultra-high vacuum conditions and thus costly equipment, so its use for preparing large-area DSCs is limited. Spin-coating and two-step dip-coating are simple processes, which can be used to prepare large CEs for DSCs. Lan et al. [21] fabricated CEs by two-step dip-coating, in which fluorine-doped tin oxide (FTO) glass was immersed in aqueous ML371, and then in poly-N-vinyl-2-pyrrolidone (PVP)-capped Pt nanocluster ink. The DSC containing the PVP-capped Pt nanocluster CE exhibited a cell efficiency of 5.28%. However, the solution contained sediment, low concentration with reuse, a short life, and resulted in considerable wastage. Wang et al. [24] prepared CEs by spin-coating, and achieved a power conversion efficiency of 5.6%. However, the area and shape of the prepared CEs were difficult to control. Compared with two-step dip-coating and spin-coating, screen-printing is simple, uses little raw material, and allows effective control. However, this method has been seldom applied, which limits the availability of large DSCs.
In the present study, we prepared a hexachloroplatinic acid paste, optimized the components for screen-printing, and then fabricated CEs by screen-printing. Adhesion testing showed that Span-85 improved adhesion. CEs prepared by screen-printing outperformed those prepared by spin-coating and two-step dip-coating. Morphological and electrochemical analyses revealed the principal factors affecting the catalytic performance of the CEs.
All reagents were of AR grade, and were hexachloroplatinic acid (Dalian Liaodong Reagent Chemical Co.), terpineol (Tianjin Bodi Chemical Co., Ltd.), γ-butyrolactone (Aladdin), Ethyl cellulose (EC) (Sigma-Aldrich), 4-tert-butyl pyridine, I2, LiI, 3-methyl-1-butyl imidazole iodine, guanidine thiocyanate, fluorine-doped tin oxide (FTO) glass (15 Ω∙□, OPVtech), TiO2 paste, Di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2'- bipyridyl-4,4'-dicarboxylato)ruthenium(II)(N719 dye, OPVtech), acetonitrile and tert-butyl alcohol (volume ratio 1:1), PVP (Aladdin), sodium borohydride (Fuchen Chemical Reagents, Tianjin, P. R. China), Triton X-100, Span-85 (Sinopharm Group Co. Ltd.), surfactant FSN and FSO (ionic fluorocarbon surfactant, DuPont).
The photovoltaic characteristics of DSCs were measured with a solar simulator (PEC-L15, Peccell, Japan) and a Keithley digital source meter (Keithley 2601, USA). Electrochemical impedance spectroscopy (EIS) was performed using a computer-controlled potentiostat (Zennium Zahner, Germany). Cyclic voltammetry (CV) and Tafel-polarization tests were conducted using an electrochemical workstation (CHI 630, CH instruments, Inc.). The surface morphologies of three Pt electrodes were observed using scanning electron microscopy (SEM) (Nova Nano SEM 450, USA). Transmission measurements were recorded using an ultraviolet (UV) spectrophotometer (HP 8453, USA).
H2PtCl6·6H2O (1 g) was dissolved in terpineol (74 g), and a 10 wt% EC solution in ethanol was added to adjust the viscosity. The terpineol solution was thoroughly mixed, and then different surfactants (Span-85, FSN, FSO, Triton X-100 or PVP, volume ratio 10:1) were added with the flatting agent 1, 4-butyrolactone (volume ratio 20:1). The solution was thoroughly stirred, and ethanol was allowed to evaporate, yielding clear paste samples. Samples containing Span-85, FSN, FSO, Triton X-100 and PVP were designated as Pt-S, Pt-N, Pt-O, Pt-T, and Pt-P, respectively.
CEs were prepared by screen-printing. FTO glass was placed on a printing tab, and a suitable press was adjusted to print single-layer paste samples. The paste samples were allowed to flow in a flat grid, and to dry at 125 °C for 10 min. Samples were then calcined at 400 °C for 30 min to yield Pt/FTO CEs. Studies reporting the spin-coated and two-step dip-coated CEs were used as references [21, 24].
A calcined TiO2 film was immersed in 3 × 10−4 mol/L N719 dye in 1:1 acetonitrile:tert-butanol for 20 h to obtain photoanode. A photoelectric performance test was carried out on the photoanode and CE in the cell [25]. The active photoanode area was 0.16 cm2. The electrolyte contained 0.06 mol/L LiI, 0.6 mol/L 1-butyl-3-methylimidazolium iodide, 0.03 mol/L I2, 0.5 mol/L 4-tert-butyl pyridine and 0.1 mol/L guanidinium thiocyanate in acetonitrile.
Current density-voltage (J-V) characteristics of the DSCs were measured under simulated AM 1.5 illumination, at an intensity of 100 mW/cm2 with a Keithley digital source meter. A symmetric dummy cell with an active area of 0.64 cm2 was subjected to EIS under dark conditions, using an electrochemical workstation at 100 mHz - 1 MHz. The bias was −0.75 V, and AC amplitude was 10 mV. EIS spectras were fitted using Zview software. The symmetric dummy cell was then subjected to a Tafel-polarization test, using an electrochemical workstation. CV curves were carried out in a three-electrode system, using Ag/Ag+ as the reference electrode, Pt as the CE, and at a scan rate of 10 mV/s. An acetonitrile electrolyte containing 0.1 mol/L LiClO4, 10 mmol/L LiI, and 1 mmol/L I2 was used.
Figure 1(a) shows the viscosity suitable for screen-printing hexachloroplatinic acid paste. The CE was fabricated by adding a surfactant to the paste (Fig. 1(c)). Two electrodes contained no surfactant, and two others contained Span-85. Adhesion was tested using 3M 810 scotch tape [31]. When the CE prepared from the paste containing surfactant was scrubbed five times, adhesion to the tape was minimal (Fig. 1(c), lower right corner). Obvious adhesion was observed when the CE without surfactant was similarly scrubbed (Fig. 1(c), upper right corner). Incorporating Span-85 increased the adhesion of the Pt nanoparticles and dispersibility of the paste. Stronger adhesion resulted in a stronger connection between the Pt nanoparticles and FTO substrate. This relationship caused the litter system impedance to match that of the latter, which increased catalytic performance. Several surfactants were used to prepare pastes (Fig. 1(b)). The transmittances and surface morphologies of the resulting CEs showed slight differences.
CEs prepared from Span-85 were compared with two other CEs. The SEM images of the three CEs are shown in Figs. 1(d), (e), and (f). Figure 1(d) shows Pt nanoparticles assembled on the CE surface by spin-coating, which was attributed to the lack of dispersibility from the absence of surfactant. Figure 1(e) shows small Pt nanoparticles uniformly dispersed on the CE surface by two-step dip-coating. This was attributed to the reduction of hexachloroplatinic acid to Pt particles. Figure 1(f) shows large Pt nanoparticles uniformly dispersed on the CE surface by screen-printing.
Transmittance was evaluated by UV-vis. absorption measurements, as shown in Fig. 2. The transmittance of the CE prepared by screen-printing was higher than that of those prepared by two-step dip-coating and spin-coating, with that of the latter two being comparable.
CV was used to assess the catalytic activity of the Pt CEs for tri-iodide reduction. Figure 3 shows CV curves of the three Pt CEs. Two typical pairs of reversible redox peaks were apparent for the three CEs [26]. The negative and positive pairs of redox peaks were attributed to the redox reactions in Eqs. (1) and (2), respectively.
I3‒ + 3e‒ ↔ 3I‒ (1)
3I2 + 2e‒ ↔ 2I3‒ (2)
The peak current densities and potentials indicated the I-/I3- reaction rates and reversibility. The peak potentials of the three CEs were similar, and the peak current density of the CE prepared by screen-printing was the highest. This indicated that the screen-printed CE had a slightly higher catalytic activity. The connectivity between the Pt nanoparticles and FTO substrate increased, when surfactant was added to the paste. This accelerated charge transfer in the external circuit, and reduced internal resistance. Thus, the reaction rate and peak current density increased.
Tafel-polarization measurements were also used to assess the catalytic activity for the I3- reduction of telluride, by the Pt CEs (Fig. 4).
The Tafel curve could be divided into three zones. The curve at high potential was attributed to the limiting diffusion zone, corresponding to the limiting diffusion current density. The curve at middle potential was the Tafel zone. Information about the exchange current density (J/i>0) was obtained, by extending the line to zero voltage, and observing the current density (J) at that point. The curve at low potential was the polarization zone [29, 30], The limiting diffusion current density of the Pt CE prepared by screen-printing was slightly higher than the others, indicating its higher activity. The connectivity between the Pt nanoparticles and FTO substrate was higher for the screen-printed CE, indicating lower charge transfer resistance and faster charge transfer, corresponding to a lower Rct.
Charge transfer at the interface between the Pt CE and electrolyte was investigated using EIS [27, 28]. Symmetric dummy cells with an active area of 0.64 cm2 were fabricated with two identical CEs spaced by 30 μm of Surlyn. Figure 5(b) shows Nyquist plots fitted with Zview software, based on the equivalent circuit model shown in Fig. 5(a).
The corresponding EIS parameters are summarized in Table 1. These include series resistance (Rs), charge transfer resistance at the electrode-electrolyte interface (Rct), capacitance at the electrode-electrolyte interface (CPE) and the Nernst diffusion impedance (ZN) [27]. The three Pt CEs exhibited similar ZN, Rs, and Rct values. The spin coated CE exhibited a higher CPE, caused by its larger Pt nanoparticles. This indicated its greater catalytic activity than that the CE prepared by two-step dip-coating. Table 1 shows that the Pt CE prepared by screen- printing exhibited low Rct and Rs values, implying an accelerated tri-iodide reduction rate, which was attributed to significant catalytic activity. This was caused by the better connectivity between Pt nanoparticles and FTO substrate, after the surfactant was added to the paste.
DSCs were fabricated containing the three Pt CEs. J-V curves are shown in Fig. 6, and the corresponding photovoltaic parameters are summarized in Table 2. The DSC containing the screen-printed Pt CE exhibited a slightly higher η of 7.3%. It exhibited a Voc of 0.70 V, Jsc of 15.49 mA/cm2 and FF of 0.67. Better connectivity between the Pt nanoparticles and FTO substrate accelerated the I3- reduction. This lowered the redox potential of the I3-/I- couple, increased the Voc, and slightly increased the η. The DSC containing the Pt CE prepared by two-step dip-coating exhibited a slightly lower η of 6.96%. The DSC containing the spin-coated CE exhibited a slightly higher η than that containing the Pt CE prepared by two-step dip-coating, indicating the former’s slightly lower Rct. The DSC containing the screen-printed CE yielded the highest η. This was because the Pt nanoparticles were uniformly distributed on the surface of the Pt CE, indicating good adhesion, low Rs and Rct. This was in agreement with the earlier EIS results.
Surfactants affected the paste properties and thus catalytic activity of the resulting screen-printed CEs. In this study, DSCs were fabricated from five Pt CEs, with each CE prepared using a different surfactant. The corresponding photovoltaic parameters are summarized in Table 3. It shows that the Pt-O/FTO DSC had a low catalytic activity, reflected in its low FF. DSCs fabricated from Pt-T/FTO, Pt-N/FTO and Pt-P/FTO CEs exhibited similar η values. That fabricated with Pt-S/FTO exhibited a slightly higher η. This was largely because of the uniformly distributed Pt nanoparticles on the CE surface, and their superior adhesion resulting in favorable catalytic activity.
Pt CEs calcined at different temperatures showed different catalytic activities (Table 4). The CE calcined at 400 °C showed the highest catalytic activity, whereas that calcined at 500 °C showed the lowest. The result was explained as follows. At 400 °C, EC and hexachloroplatinic acid slowly disintegrated, resulting in smaller uniformly distributed Pt nanoparticles. At 500 °C, hexachloroplatinic acid and EC disintegrated much faster, resulting in larger non-uniformly distributed Pt nanoparticles.
DSC CEs where prepared by adding Span-85 to the paste, which enhanced the adhesion of Pt particles on the FTO substrate. We analyzed factors affecting the performance of the CE prepared by screen-printing, and compared its properties with those of CEs prepared by two-step dip-coating and spin- coating. The Pt CE prepared by screen-printing exhibited a high light transmittance, uniform Pt nanoparticle distribution, favorable catalytic performance, controllable electrode area, and a power conversion efficiency of 7.30% when incorporated in a DSC. Screen-printing is suitable for the large-scale low cost fabrication of DSC CEs.
自从上世纪90年代染料敏化太阳能电池(DSCs)被首次报道以来[1], 因其具有较高的理论转换效率、低成本、无毒环保及弱光下光电转换效率高等特点而引起了广泛关注[2, 3, 4]. 对电极是影响染料敏化太阳能电池性能的重要因素. 它主要起到收集外电路电子及催化电解液中氧化还原电对氧化还原反应的作用.常用的对电极主要有铂对电极[5]和非铂对电极. 非铂对电极主要有金属碳化物、金属氧化物、金属氮化物、金属硫化物[6, 8, 9, 10, 11]、纯碳材料[12]、复合材料[7, 13, 14, 15]对电极等.
非铂催化材料是现阶段染料敏化太阳能电池研究的热点, 但因其性能不稳定,而受到了限制. 铂对电极因其稳定性和催化活性较高而仍然广受关注. 研究者开发了一系列制备铂对电极的方法,以减少铂的使用量并简化制备条件. 制备染料敏化太阳能电池铂对电极的方法已经由磁控溅射法[16, 17]、化学还原法[18]、电沉积法[19, 20]等逐步发展到两步浸泡法[21, 22, 23]及旋涂热解法等[24]. 磁控溅射等方法需高真空, 成本较高, 因而使它在染料敏化太阳能电池的大面积开发及应用中受到了限制. 目前较易实验制备大面积染料敏化太阳能电池对电极的方法是旋涂热分解法和两步浸泡法. Lan等[21]采用两步浸泡法制备铂对电极, 使用清洁整孔剂ML371处理FTO玻璃基板, 然后浸泡在用聚N-乙烯基吡咯烷酮(PVP)包覆铂颗粒的水溶液中制作对电极, 组成的DSCs器件取得了较高的光电转换效率, 达到了5.28%. 但是该方法存在着PVP包覆的铂溶液的沉淀, 多次使用浓度降低等现象, 使用时间短且容易浪费. Wang等[24]采用旋涂热分解法制备了Pt/FTO对电极, 其光电转换效率达5.6%. 但是该法受仪器托盘限制, 不容易控制铂电极的面积及形状. 比较而言, 丝网印刷操作更简单、使用量更低、可控性更好, 但是目前相关报道并不多.
因此, 本文首先制备适合丝网印刷的氯铂酸浆料并对其组分进行了优化, 再用丝网印刷技术将其制备成对电极, 并与两步浸泡法、旋涂热分解法制备的对电板进行了系统的比较, 通过形貌和电化学行为, 分析了影响对电极催化性能的关键因素.
将1 g H2PtCl6·6H2O (大连辽东试剂化学公司)溶解于74 g的松油醇(天津博迪化工股份有限公司)中, 再加入适量的10 wt%的乙基纤维素(EC, 西格玛奥德里奇)的乙醇溶液调整其粘度, 混合均匀后取5份同等量的溶液, 分别加入适量的表面活性剂Span-85 (国药集团化学试剂有限公司), FSN, FSO (离子型氟碳表面活性剂, 杜邦), Triton X-100或PVP (聚乙烯基吡咯烷酮), 表面活性剂与松油醇的体积比是1:10, 最后加入流平剂γ-丁内酯(阿拉丁, 流平剂与松油醇的体积比为1:20)搅拌混合均匀后蒸发除去其中的乙醇得到澄清的浆料, 分别命名为Pt-S, Pt-N, Pt-O, Pt-T和 Pt-P.
采用丝网印刷法制作对电极, 将FTO玻璃基板置于印刷台上, 调整合适的压力印刷一层氯铂酸浆料, 带流平消除网格印后, 在125 oC下干燥10 min, 然后在400 oC焙烧30 min, 冷却至室温后即得到Pt/FTO对电极.
参照文献[21, 24]采用两步浸泡法和旋涂方法制作对电极.
将焙烧后的TiO2薄膜浸泡于N719 (奥匹维特)的叔丁醇和乙腈(体积比1:1)溶液中(3 x 10-4 mol/L) 20 h制成光阳极, 将光阳极与对电极组装成电池进行光电性能测试[25]. 光阳极的活性面积为0.16 cm2, 电解液采用0.03 mol/L I2, 0.06 mol/L LiI, 0.6 mol/L 1-丁基-三甲基咪唑碘, 0.1 mol/L异硫氰酸胍, 0.5 mol/L叔丁基吡啶(奥匹维特)的乙腈溶液.
光阳极、对电极和电解液组成的DSC组件在AM1.5，光照强度100 mW/cm2的模拟太阳光(PEC-15, Peccell, 日本)下,采用Keithly数字源表(Keithley-2601, 吉时利, 美国)进行光电性能测试, 得到光电流密度-光电压(J-V)曲线. 两块相同的对电极(面积0.64 cm2)组成对称电池在电化学工作站(IMe6X, ZAHNER ZENNIUM,德国)在暗态下进行电化学阻抗测试(两电极体系), 扫描范围100 mHz-1 MHz, 施加偏压-0.75 V, 振幅10 mV,用ZView软件进行EIS拟合. 两块相同的对电极(面积0.64 cm2)组成对称电池在电化学工作站(CHI 630, 辰华, 上海)下进行Tafel极化曲线测试. CV曲线采用三电极体系, 参比电极为Ag/Ag+, 对电极为铂丝, 电解液为0.1 mol/L LiClO4, 10 mmol/L LiI和1 mmol/L I2, 扫描速率10 mV/s.
图1(a)是制备的具有一定黏度的、适合丝网印刷的氯铂酸浆料. 在浆料中, 加入表面活性剂前后制备的对电极如图1(c)所示, 两片对电极浆料中无表面活性剂, 其它两片对电极浆料中均加入了Span-85, 用型号3M810丝高胶带对对电极进行附着力测试[31], 加入了表面活性剂的对电极, 在胶带上来回擦拭5次后, 揭开胶带, 胶带上无明显粘附(图1(c)); 而不加入表面活性剂的对电极, 胶带表面粘附严重(图1(c)右下). 这表明Span-85的加入有利于增加铂的附着力和分散性, 附着力越好, 铂粒子与导电基底的连接性越好, 其系统阻抗越小, 这对铂对电极的催化性能有一定的影响. 本文采用了多种表面活性剂来制备浆料(图1(b)), 所制备的铂对电极的表面形态和透光率有所差别.
经过筛选, 我们将采用Span-85制备的铂对电极与其它两种方法制备的进行系统比较. 图1(d), (e)和(f)是三种对电极的SEM照片如图1(d)所示, 使用旋涂热分解法制备的对电极表面铂的团聚比较严重,这可能是因不使用表面活性剂而影响了铂纳米粒子的分散所致. 由图1(e)可见, 采用两步浸泡法制备的单质铂分散均匀, 这可能是由于铂粒子是由氯铂酸经化学还原形成的. 如图1(f)所示, 使用丝网印刷法制备的对电极其表面铂粒子较大且分布均匀. 利用紫外可见吸收光谱(UV-vis, HP8453, 美国)检测三种电极的透光率, 如图2所示, 旋涂热分解法制备的Pt/FTO对电极的透光率最高, 而其它两种方法制备的是相当的.
采用CV曲线对几种对电极催化I3-/I-的氧化还原反应进行了研究, 图3是三种Pt/FTO对电极的CV曲线. 可以看出, 几种对电极都出现两对氧化还原峰[26], 较低电位处的对应于反应(1), 而较高电位处的则对应于反应(2), 具体如下.
I3- + 3e- ↔ 3I- (1)
3I2 + 2e- ↔ 2I3- (2)
峰电流和峰电位值分别代表了I-/I3-氧化还原反应的快慢程度以及可逆性. 可以看到, 三种Pt/FTO对电极的氧化还原峰位置比较接近, 但是丝网印刷法制备的Pt/FTO对电极的峰电流密度较大说明其具有较高的催化性能. 这主要是因为在浆料中加入表面活性剂, 可以有效改善Pt纳米粒子与导电基底之间的连接性, 印刷铂电极的铂粒子与基板之间的结合较牢固, 有效改善了电荷交换,降低了内阻,导致外电路电荷的传输速率较快, 化学反应速率较快, 因而具有较大的峰电流.
3.2.2. Tafel极化曲线表征催化反应的扩散性能
本文还采用Tafel极化曲线对三种Pt/FTO对电极进行了研究, 结果见图4. 可以看出, Tafel极化曲线可分为三个区域:高电位区为扩散区, 此时的扩散电流密度即为极限扩散电流密度; 中间电位区为Tafel区, 该区切线的延长线与平衡电位的交点处的电流密度(J)即为交换电流密度(J0), 低电位区为极化区[29, 30]. 可以看出, 三种Pt/FTO对电极均能有效的催化I3-/I-之间的氧化还原反应; 同时, 丝网印刷法制备的Pt/FTO对电极其极限扩散电流密度和交换电流密度均略高于其他两种方法制备的, 说明其催化性能略高. 这可能是由于铂粒子与基板附着力较好, 电化学阻抗较小, 电荷交换速率快; 这与其具有相对较小的传荷电阻Rct是对应的.
采用EIS谱测试了几种对电极/电解液界面之间的传荷性能[27, 28]. 将两块对称的面积为0.64 cm2对电极组成对称电池, 两块对电极之间夹一层30 μm厚的沙林膜做隔离层. 图5(a)是等效电路图, 图5(b)是其Nyquist阻抗图谱.根据等效电路图拟合得到的数据列于表1中, 其中, Rs表示串联电阻; Rct表示电解液与电极之间的电荷交换电阻; CPE表示相应的电容; ZN表示电解液中的氧化还原电对(I3-/I-)的Nyquist扩散电阻[27]. 结果显示, 旋涂热分解法和两步浸泡法制备的Pt/FTO对电极的Rs,& #8197;Rct和ZN差别不大, 但前者的CPE较大, 这可能是由于铂粒子负载量大所致. 该法制备的铂对电极活性要高于两步浸泡法的. 如表1所示, 比较而言, 丝网印刷法制备的Pt/FTO对电极Rs和Rct较小, 表明其具有较好的导电性.这是由于表面活性剂的加入能够增加铂粒子与基板之间的附着力, 说明其具有较高的催化活性.
对三种对电极组装的DSCs进行光电性能测试(J-V), 结果见图6和表2. 可以看出, 丝网印刷法制备的Pt/FTO对电极组装的DSCs的开路电压、短路电流密度和填充因子分别是0.70 V, 15.49 mA和0.67, 光电转换效率达到了7.30%, 略高于其他二种. 这主要是由于其具有较高的开路电压所致, 丝网印刷法制备的Pt/FTO对电极附着力好, 催化效率高, I3-的还原速率快, I3-/I-的氧化还原电势较低, 开路电压较高. 而两步浸泡法制作的Pt/FTO对电极的DSCs光电转换效率稍低, 为6.96%. 旋涂法制备的Pt/FTO对电极传荷电阻略低于浸泡法的, 其组装而成的DSCs的光电转换效率也略高. 丝网印刷法制备的Pt/FTO对电极组装的电池具有最高的效率是由于其对电极表面分布均匀,附着力好, Rs和Rct均较小, 与EIS结果一致.
使用丝网印刷法制备Pt/FTO对电极, 表面活性剂的种类将影响浆料的状态和对电极的催化活性. 表3比较了5种表面活性剂制备的对电极组装DSCs的效率. 可以看出, 对电极Pt-O的填充因子和催化活性均较低. Pt-T/FTO, Pt-N/FTO和Pt-P/FTO对电极在DSCs中光电转换效率比较接近, 而Pt-S对电极的较高, 主要是因为该对电极表面均匀, 附着力好, 催化性能优异.
不同温度烧结所得对电极的催化活性不同(表4), 其中400 oC时最高, 而在500 oC时最低. 这可能是因为温度较低时, 氯铂酸及乙基纤维素分解速率较慢, 颗粒较小, 分布均匀; 而当温度升高时, 氯铂酸及乙基纤维素分解速度增大, 颗粒粒径增大, 导致粒子分布不均匀.
通过引入Span-85改进了对电极的制备方法, 显著改善所制对电极的附着力, 并与两步浸泡法和旋涂热解法进行了系统对比, 分析了影响对电极催化性能的主要因素. 结果表明, 丝网印刷法制备的Pt/FTO对电极具有较高的透光率,铂分布均匀, 催化性能优异, 面积可控, 在染料敏化太阳能电池中的效率达7.30%. 该法更适合大面积制作对电极, 有利于降低生产成本.
2014, Vol. 35 Issue (2): 219-226
PDF (709KB)
2014, Vol. 35 Issue (2): 219-226
PDF (709KB)