Optimization Of Monolithic All-Solid-State Dye-Sensitized Solar Cells

Dye-sensitized nanocrystalline solar cell (DSSC) is a new kind of solar cell, which was firstly developed in1990s. Because of its low cost materials and simple fabrication process, DSSC has attracted great attention from researchers and investors. From its different electrolytes, DSSC is mainly divided into the liquid DSSC and the solid-state DSSC. Among them, the liquid DSSC meets many problems such as solvent evaporation and electrolyte leakage, which hinder its large-scale application. In contrast, the solid-state DSSC mainly apply hole transporting materials to replace the liquid electrolyte. Compared with the liquid DSSC, the solid-state DSSC avoid electrolyte evaporation or leakage problems. Moreover, the solid-state DSSC is mainly created with monolithic structure, where the photoanode and the counter electrode are integrated on a single conductive substrate, which further reduces the cost of the device. As a result, the monolithic all-solid-state DSSC has more application prospect than the liquid DSSC.Monolithic all-solid-state DSSC is mainly composed of photoanode, hole transporting materials and counter electrode. At present, monolithic all-solid-state DSSC mainly suffer from complicated fabrication low efficiency. The most complicated process in tranditional monolithic all-solid-state DSSC is the fabrication of counter electrode:depositing a metal layer (Au or Ag) on the hole transporting matertial under high vacuum. Currently, there are only a few the research on the counter electrode of monolithic all-solid-state DSSC. Therefore, the development of new materials and process of counter electrode is indispensable. In addition, dye, hole transporting materials and photoanode also need improvement for monolithic all-solid-state DSSC.Herein, based on printable carbon material as counter electrode (CE) instead of traditional evaporated metal electrode, we investigate the effect of the carbon CE structure on the performance for all-solid-state DSSC based on poly(3-hexylthiophene)(P3HT). Meanwhile, for the hole transporting material P3HT, near-infrar dye SQ2was used to study the incident photon to electron conversion efficiency. For the hole transporting material spiro-OMeTAD, the influence of photo-doping on the performance of devices was investigated. In addition, the effect of photoanode structure on the performance of monolithic all-solid-state DSSC was studied. The main contents of this thesis are listed as following:Firstly, due to the complicated fabrication of counter electrode for monolithic solid-state DSSC, graphite and carbon black composite material was used as CE to fabricate P3HT-based monolithic solid-state DSSC by screen printing. The influence of CE structure and the thickness of insulating layer and photoanode layer on the performance for devices were studied. After optimization, an efficiency up to3.11%was achieved for the monolithic solid-state DSSC under a standard solar illumination (AM1.5100mW cm-2).Secondly, due to the absorption competition between P3HT and D102dye, the near infrared squarine dye SQ2sensitizer was used to fabricate P3HT-based monolithic solid-state DSSC, and the effects of molecular structure of SQ2and LiTFSI treatment on the performance of the devcies were investigated. An efficiency of2.2%was achieved within monolithic solid-state DSSC based on SQ2and P3HT.Thirdly, spiro-OMeTAD was used as a hole transporting material to fabricate monolithic solid-state DSSC based on mesoporous carbon CE. The effect of photo-doping on the performance of devices was investigated. Moreover, the influences of photo-doping on the charge recombination at spiro-OMeTAD/C interface and on the charge transfer at TiO2/spiro-OMeTAD interface were analyzed. Through the optimization on the level of photo-doping, an efficiency of4.04%was achieved within spiro-OMeTAD based monolithic solid-state DSSC with carbon CE.Finally, due to the insufficient light trapping for traditional photoanode, mesoporous TiO2beads was used as photoanode to fabricate monolithic solid-state DSSC based on spiro-OMeTAD and an efficiency of4.0%was achieved. The effect of TiCl4treatment on the photovoltaic performance for TiO2beads phonoanode and P25nanoparticles phonoanode were studied. The scattering properties and electron transport properties of the two photoanodes were also investigated.