The Modification Of TiO₂ Photoanode And Tandem DSSCs For Application In Water Splitting

Currently, the response to the global energy crisis is undoubtedly one of the important scientific challenges. Developing low cost of clean and renewable energies has attracted extensive attention of scientistsand entrepreneurs around the world. How to effectively develop and use solar energy and convert it into electricity is one of the important topics. DSSC has the advantages such as low cost, environment friendly. Modification of photoanode by doping is an effective way to improve the efficiency of DSSC photoelectric. In this work, we used covalent organic porous materials (COP) doped photoanode to effectively improve the photoelectric conversion efficiency of DSSC, and further fabricated the tandem DSSCs for application in electrolytic hydrogen aquatic, which provides a new strategy for the development of clean, efficient, green hydrogen.The main contents are as follows:(1) We prepared the anatase TiO2 nanoparticles about 20 nm by using commercial anatase crystal type of TiO2 slurry of 200-900 nm. We fabricated six kinds of photoanode with different thickness and structures, and test the J- V characteristics. Results indicate that TiO2 photoanode film with 26 nm thickness contains an electronic scattering layer and three transport layers, and the corresponding DSSC received the highest PCE of 8.47%, where Jsc is 20.57 mA/cm2, Voc is 0.704 V and FF is 58.5%.(2) The COP-64 was synthesized by the Yamamoto coupled reaction, different levels of COP-64 powder were doped into the TiO2 slurry through the physical method, and different contents of COP-64@ TiO2 slurries were obtained. The COP-64 content is 0.0%,0.2%,0.4%,0.6%,0.4% and 1.0%, respectively. The results indicate that with the increase in the COP-64 doping content, the current density first increases and then decreases, while the open circuit voltage and fill factor and the photoelectric conversion efficiency also appear the same rule. However, when the COP-64 content is 0.6%, the biggest PCE of 9.97% was obtained, accompanying with Jsc of 22.56 mA/cm2, Voc of 0.68V and FF of 62.3%. The PCE gets an improvement of 27.3% compared to the DSSC without doping COP-64.We also assembled the tandem COP-64@TiO2-based DSSCs. The PCEs of single, two tandem and three tandem DSSCs are 9.83%,9.40% and 9.06%, respectively. With the increase the tandem number of series of DSSCs, the PCE of the tandem DSSCs decreases slightly, and Voc increases while Jsc decreases. Voc of three tandem DSSCs reaches 1.966 V. Jsc of a single DSSC is 22.96 mA/cm2, and two pieces of DSSCs reduces to 11.55 mA/cm2, and three pieces of DSSCs reduces to 7.27 mA/cm2, which is caused by the photoanode area multiplied. Electrolysis of water is successfully achieved by designing and assembling the solar cells-electrolysis of water system, and amount of hydrogen production was measured by gas chromatography. Monolithic tandem DSSCs provides the voltage for electrolysis of water, because three series of DSSCs voltage reaches 1.96 V, meeting the minimum theoretical voltage (1.23V) electrolysis of water. Finally, we get the solar-to-hydrogen conversion efficiencies (?STH) up to 7.45%.