Testing two concepts to increase the efficiency of p-type dye-sensitized solar cells

廉价的太阳能是减少二氧化碳排放和防止全球变暖的关键因素之一。染料敏化太阳能电池（dsc）价格便宜，具有较短的能量回收期，并且在漫射光下表现出良好的性能，这使得它们在商业应用方面非常有吸引力。到目前为止，dsc的光电转换效率不超过13%。带有光阳极的DSC （n-DSC）适合商业应用，而最有效的带有光电阴极的DSC （p-DSC）只有大约十分之一的功率转换效率，对于商业应用来说太低了。构建高效的p-DSC不仅为商业应用提供了一种新型的DSC，也是构建具有光活性阳极和光活性阴极（np-DSC）的高性能DSC的里程碑。这些器件可以拥有比单个模块更高的功率转换效率。在此应用中，提出了两个概念来提高p- dsc的光电转换效率。第一个概念是在p- dsc中结合使用离子液体和过渡金属氧化还原介质。离子液体的阴离子应该比阳离子更接近半导体中的注入空穴，如带正电的过渡金属配合物，作为氧化还原介质，这似乎是合理的。因此，离子液体的使用可能会降低p- dsc的高暗电流，从而限制了p- dsc的功率转换效率。第二个概念是氧化还原介质在染料上的临时对接。以路易斯基为基块的染料可以在过渡金属络合物上配位。染料与带正电的氧化还原介质的紧密接触会提高从染料到氧化还原介质的首选电子转移速率，同时会增加染料与半导体之间的非期望电子复合速率。如果从染料转移到氧化还原介质的电子位于过渡金属配合物的反键d轨道上，染料和氧化还原介质之间的键应被削弱。因此，如果染料提供强配位配体，则在染料上配位的还原氧化还原介质可以被溶液中氧化形式的氧化还原介质所取代。此替换将恢复设备中的初始配置。如果临时氧化还原介质对接染料的概念或离子液体与过渡金属氧化还原介质的结合使用可以作为提高p-DSC效率的一般概念，那么后续项目将重点关注器件性能优化，以构建高效的p-DSC和新一代dsc， np- dsc光电转换效率超过13%。

Cheap solar energy sources are one of the key factors to reduce carbon dioxide emission and prevent global warming. Dye-sensitized solar cells (DSCs) are cheap, possess a short energy payback time, and show a good performance at diffuse light, which make them very attractive for commercial applications. So far, DSCs do not exceed 13% light-to-electricity conversion efficiency. While DSCs with a photoanode (n-DSCs) are suitable for commercial applications, the most efficient DSC with a photocathode (p-DSCs) shows only about one-tenth power conversion efficiency, significantly too low for commercial applications. Building a high efficient p-DSC would not only provide a new type of DSC for commercial applications, it is also a milestone in the construction of high-performance DSCs with a photoactive anode and a photoactive cathode (np-DSC). These devices can possess a significantly higher power conversion efficiency than their individual modules. Within this application, two concepts are addressed to increase the light-to-electricity conversion efficiency of p-DSCs.The first concept is the usage of ionic liquids in combination with transition metal redox mediators in p-DSCs. It seems reasonable that the anions of ionic liquids should be closer to injected holes in the semiconductor than cations, like positively charged transition metal complexes which serve as redox mediator. Thus, the usage of ionic liquids might decrease the high dark current of p-DSCs which limits the power conversion efficiency of p-DSCs. The second concept is a temporary docking of the redox mediator at the dye. A dye with a Lewis basic group as building block can coordinate at a transition metal complex. The close contact of the dye and the positively charged redox mediator should enhance the preferred electron transfer rate from the dye to the redox mediator while the undesired electron recombination rate between dye and semiconductor should be increased. If the electron transferred from the dye to the redox mediator resides in an antibonding d-orbital of the transition metal complex, the bond between the dye and the redox mediator should be weakened. As a result, the reduced redox mediator coordinated at the dye can be replaced by the oxidized form of the redox mediator in solution if the dye offers a strongly coordinating ligand. This replacement will restore the initial configuration in the device.If the concept of temporary redox mediator docking at the dye or the usage of ionic liquids in combination with transition metal redox mediators can be shown as general concept to increase the efficiency of a p-DSC, a follow-up project will focus on device performance optimizations to construct highly efficient p-DSCs and a new generation of DSCs, np-DSCs exceeding 13% light-to-electricity conversion efficiency.