Department of Chemistry & Biochemistry, University of Arizona , Tucson, Arizona 85721, United States.
Institute of Materials for Electronics and Energy Technology, Friedrich-Alexander-University Erlangen-Nuremberg , Martensstrasse 7, 91058 Erlangen, Germany.
ACS Appl Mater Interfaces. 2016 Aug 3;8(30):19787-98. doi: 10.1021/acsami.6b02792. Epub 2016 Jul 25.
This report focuses on the evaluation of the electrochemical properties of both solution-deposited sol-gel (sg-ZnO) and sputtered (sp-ZnO) zinc oxide thin films, intended for use as electron-collecting interlayers in organic solar cells (OPVs). In the electrochemical studies (voltammetric and impedance studies), we used indium-tin oxide (ITO) over coated with either sg-ZnO or sp-ZnO interlayers, in contact with either plain electrolyte solutions, or solutions with probe redox couples. The electroactive area of exposed ITO under the ZnO interlayer was estimated by characterizing the electrochemical response of just the oxide interlayer and the charge transfer resistance from solutions with the probe redox couples. Compared to bare ITO, the effective electroactive area of ITO under sg-ZnO films was ca. 70%, 10%, and 0.3% for 40, 80, and 120 nm sg-ZnO films. More compact sp-ZnO films required only 30 nm thicknesses to achieve an effective electroactive ITO area of ca. 0.02%. We also examined the electrochemical responses of these same ITO/ZnO heterojunctions overcoated with device thickness pure poly(3-hexylthiophehe) (P3HT), and donor/acceptor blended active layers (P3HT:PCBM). Voltammetric oxidation/reduction of pure P3HT thin films on ZnO/ITO contacts showed that pinhole pathways exist in ZnO films that permit dark oxidation (ITO hole injection into P3HT). In P3HT:PCBM active layers, however, the electrochemical activity for P3HT oxidation is greatly attenuated, suggesting PCBM enrichment near the ZnO interface, effectively blocking P3HT interaction with the ITO contact. The shunt resistance, obtained from dark current-voltage behavior in full P3HT/PCBM OPVs, was dependent on both (i) the porosity of the sg-ZnO or sp-ZnO films (as revealed by probe molecule electrochemistry) and (ii) the apparent enrichment of PCBM at ZnO/P3HT:PCBM interfaces, both effects conveniently revealed by electrochemical characterization. We anticipate that these approaches will be applicable to a wider array of solution-processed interlayers for "printable" solar cells.
本报告重点评估了溶液沉积溶胶-凝胶（sg-ZnO）和溅射（sp-ZnO）氧化锌薄膜的电化学性能，这些薄膜旨在用作有机太阳能电池（OPV）中的电子收集层。在电化学研究（伏安和阻抗研究）中，我们使用了涂有 sg-ZnO 或 sp-ZnO 中间层的氧化铟锡（ITO），与纯电解质溶液或带有探针氧化还原对的溶液接触。通过仅对氧化物中间层进行电化学响应表征，并从带有探针氧化还原对的溶液中测量电荷转移电阻，来估计 ZnO 中间层下暴露的 ITO 的电活性面积。与裸 ITO 相比，sg-ZnO 薄膜的有效电活性 ITO 面积约为 40、80 和 120nm sg-ZnO 薄膜的 70%、10%和 0.3%。更致密的 sp-ZnO 薄膜仅需 30nm 厚度即可获得约 0.02%的有效电活性 ITO 面积。我们还研究了这些相同的 ITO/ZnO 异质结在覆盖器件厚度纯聚（3-己基噻吩）（P3HT）和施主/受主共混活性层（P3HT:PCBM）后的电化学响应。在 ZnO/ITO 接触处，纯 P3HT 薄膜的伏安氧化/还原表明 ZnO 薄膜中存在允许暗氧化（ITO 空穴注入到 P3HT 中）的针孔途径。然而，在 P3HT:PCBM 活性层中，P3HT 氧化的电化学活性大大减弱，这表明 PCBM 在 ZnO 界面附近富集，有效地阻止了 P3HT 与 ITO 接触的相互作用。从全 P3HT/PCBM OPV 的暗电流-电压行为中获得的旁路电阻取决于（i）sg-ZnO 或 sp-ZnO 薄膜的多孔性（通过探针分子电化学揭示）和（ii）PCBM 在 ZnO/P3HT:PCBM 界面处的明显富集，这两种效应都可以通过电化学表征方便地揭示。我们预计这些方法将适用于更广泛的用于“可印刷”太阳能电池的溶液处理中间层。
