Optimization Of Monolithic All-solid-state Dye-sensitized Solar Cells

Dye-sensitized nanocrystalline solar cell (DSSC) is a new kind of solar cell, whichwas firstly developed in1990s. Because of its low cost materials and simple fabricationprocess, DSSC has attracted great attention from researchers and investors. From itsdifferent electrolytes, DSSC is mainly divided into the liquid DSSC and the solid-stateDSSC. Among them, the liquid DSSC meets many problems such as solvent evaporationand electrolyte leakage, which hinder its large-scale application. In contrast, the solid-stateDSSC mainly apply hole transporting materials to replace the liquid electrolyte. Comparedwith the liquid DSSC, the solid-state DSSC avoid electrolyte evaporation or leakageproblems. Moreover, the solid-state DSSC is mainly created with monolithic structure,where the photoanode and the counter electrode are integrated on a single conductivesubstrate, which further reduces the cost of the device. As a result, the monolithicall-solid-state DSSC has more application prospect than the liquid DSSC.Monolithic all-solid-state DSSC is mainly composed of photoanode, hole transportingmaterials and counter electrode. At present, monolithic all-solid-state DSSC mainly sufferfrom complicated fabrication and low efficiency. The most complicated process intraditional 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 research on the counter electrode of monolithicall-solid-state DSSC. Therefore, the development of new materials and process of counterelectrode is indispensable. In addition, dye, hole transporting materials and photoanodealso need improvement for monolithic all-solid-state DSSC.Herein, based on printable carbon material as counter electrode (CE) instead oftraditional evaporated metal electrode, we investigate the effect of the carbon CE structureon 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 tostudy the incident photon to electron conversion efficiency. For the hole transportingmaterial spiro-OMeTAD, the influence of photo-doping on the performance of deviceswas 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 asfollowing:Firstly, due to the complicated fabrication of counter electrode for monolithicsolid-state DSSC, graphite and carbon black composite material was used as CE tofabricate P3HT-based monolithic solid-state DSSC by screen printing. The influence ofCE structure and the thickness of insulating layer and photoanode layer on theperformance for devices were studied. After optimization, an efficiency up to3.11%wasachieved 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 nearinfrared squarine dye SQ2sensitizer was used to fabricate P3HT-based monolithicsolid-state DSSC, and the effects of molecular structure of SQ2and LiTFSI treatment onthe performance of the devcies were investigated. An efficiency of2.2%was achievedwithin monolithic solid-state DSSC based on SQ2and P3HT.Thirdly, spiro-OMeTAD was used as a hole transporting material to fabricatemonolithic solid-state DSSC based on mesoporous carbon CE. The effect of photo-dopingon the performance of devices was investigated. Moreover, the influences of photo-dopingon the charge recombination at spiro-OMeTAD/C interface and on the charge transfer atTiO2/spiro-OMeTAD interface were analyzed. Through the optimization on the level ofphoto-doping, an efficiency of4.04%was achieved within spiro-OMeTAD basedmonolithic solid-state DSSC with carbon CE.Finally, due to the insufficient light trapping for traditional photoanode, mesoporousTiO2beads was used as photoanode to fabricate monolithic solid-state DSSC based onspiro-OMeTAD and an efficiency of4.0%was achieved. The effect of TiCl4treatment onthe photovoltaic performance for TiO2beads phonoanode and P25nanoparticlesphonoanode were studied. The scattering properties and electron transport properties ofthe two photoanodes were also investigated.