Direct Comparison of Electron Transport and Recombination Behaviors of Dye-Sensitized Solar Cells Prepared Using Different Sintering Processes

Flexible dye-sensitized solar cells on plastic substrates have achieved a conversion efficiency of 8.6% with the hot compression technique (<150 degrees C). However, the value of efficiency is only 70% of that achieved using glass substrates with high-temperature sintering technique (500 degrees C). Investigating the origin of this difference is a critical step for further improving the performance of plastic dye-sensitized solar cells. In this study, an optimized ternary viscous titania paste without the addition of organic binders enables the fabrication of efficient dye-sensitized solar cells with a low-temperature process. Therefore, the electron-transport behavior of dye-sensitized solar cells can be directly compared with those prepared with the high-temperature sintering technique. In addition to the structural and optical differences, the hot compressed photoanode of dye-sensitized solar cells have an electron diffusion coefficient that is 2 times smaller and a recombination time that is 6 times shorter than those of the high-temperature sintered cells, suggesting inadequate interparticle connections and more recombination events. These results indicate that electron transport and recombination are still the key factors governing the performance of low-temperature fabricated dye-sensitized solar cells. Eventually, the flexible cell with an efficiency of 6.81% has been achieved on flexible indium tin oxide/polyethylene naphthalate substrate. Further improvements in advanced low-temperature processing or novel materials with minimized defect or grain boundaries are required.This work was supported by the Open Fund of the Key Laboratory of Optical Information Science & Technology, Ministry of Education of China (Nankai University), the Fundamental Research Funds for the Central Universities of China, the International Cooperation Project of the Ministry of Science and Technology (2014DFE60170), National Natural Science Foundation of China (Grant Nos. 61474065 and 61674084), Tianjin Research Key Program of Application Foundation and Advanced Technology (15JCZDJC31300), the Green Channel Project of Tianjin Natural Science Foundation (17JCYBJC41400), and the 111 Project (B16027). M.J.K. thanks the Global Frontier R&D Program on Center for Multiscale Energy System (2012M3A6A7054856), the Technology Development Program to Solve Climate Changes (2017M1A2A2087353), and Research Program (2018R1A2B2006708) funded by the National Research Foundation under the Ministry of Science, ICT & Future Planning, Republic of Korea, and The Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (No. 20173010013200)