Okello Alex, Owuor Brian Owino, Namukobe Jane, Okello Denis, Mwabora Julius
Department of Physics, Makerere University, P.O. Box 7062, Kampala, Uganda.
Department of Physics, University of Nairobi, P.O. Box 30197-00100, Nairobi, Kenya.
Heliyon. 2022 Jul 9;8(7):e09921. doi: 10.1016/j.heliyon.2022.e09921. eCollection 2022 Jul.
The influence of the pH of anthocyanins on photovoltaic performance in dye-sensitized solar cells has been investigated. Anthocyanins were extracted from crushed leaf stocks of Crantz (Cassava plant) using methanol acidified with 0.5% trifluoracetic acid. The filtrate was concentrated using a rotary evaporator and partitioned against ethyl acetate. The anode was prepared by screen printing TiO paste on a previously cleaned fluorine-doped tin oxide (FTO) glass substrate. The cathode was made by applying plastisol on a previously cleaned FTO glass substrate using an artistic brush and later annealed at 450 °C for 20 min to activate platinum. The performance of the solar cells was measured using a solar simulator fitted with an AM1.5 air filter. Electron transport was studied using electrochemical impedance spectroscopy (EIS). It was observed that the short circuit current and efficiency dropped from pH 2 to pH 6 and peaked at pH 8, with values of 0.399 mA and 0.390%, respectively. It then drops further as the basicity increases. The open circuit voltage was observed to increase consistently from pH 2 to pH 12. EIS results showed that the electron density in the conduction band of TiO increases from pH 2 to pH 10 and drops from pH 10 to pH 12. It was concluded that, while a large number of electrons are injected into the conduction band of TiO the majority do not contribute to the current but instead recombine with other electron acceptor species in the solar cell. However, the injected electrons cause an upwards shift in the quasi-Fermi level of electrons in the conduction band of TiO. This explains the large variation in the open circuit voltage compared to the short circuit current.
研究了花青素的pH值对染料敏化太阳能电池光伏性能的影响。使用用0.5%三氟乙酸酸化的甲醇从Crantz（木薯植物）的粉碎叶茎中提取花青素。滤液用旋转蒸发仪浓缩，并用乙酸乙酯进行分配。通过在预先清洁的掺氟氧化锡（FTO）玻璃基板上丝网印刷TiO糊剂来制备阳极。通过用美工刷将增塑溶胶涂覆在预先清洁的FTO玻璃基板上制备阴极，然后在450℃下退火20分钟以活化铂。使用配备AM1.5空气过滤器的太阳能模拟器测量太阳能电池的性能。使用电化学阻抗谱（EIS）研究电子传输。观察到短路电流和效率从pH 2降至pH 6，并在pH 8时达到峰值，分别为0.399 mA和0.390%。然后随着碱度增加进一步下降。观察到开路电压从pH 2到pH 12持续增加。EIS结果表明，TiO导带中的电子密度从pH 2增加到pH 10，并从pH 10下降到pH 12。得出的结论是，虽然大量电子注入到TiO的导带中，但大多数电子对电流没有贡献，而是与太阳能电池中的其他电子受体物种复合。然而，注入的电子导致TiO导带中电子的准费米能级向上移动。这解释了与短路电流相比开路电压的巨大变化。
