The Optimization And Design Of Counter Electrodes For Mesoscopic Solar Cells

Mesoscopic solar cell is a new kind of solar cell, which has a unique mesoporous structure. Compared to other kinds of photovoltaic devices, the solar cell with mesoscopic structure possesses larger specific surface area, helping to capture more photon and result in larger photocurrent.Dye-sensitized solar cells (DSSC) are one typical mesoscopic solar cell. Commonly, they employ mosoporous TiO2nanocrystalline as the photoelectrode. This kind of photoelectrode has a large specific surface area up to285m/g, which is780times larger than the planar photoelectrode. Up to now, the photoelectric conversional efficiency (PCE) of the mesoscopic solar cell based on mesoporous photoelectrde has exceeding15%, which is comparable to that of the conversional Si version. Moreover, the cost of DSSC is much lower and the fabricating process is much easier, making DSSC possess larger application potential.Usually, DSSC can be divided into two categoties:the liquid-state DSSC and the solid-state DSSC. The liquid-state DSSC generally employ Pt as counter electrode while the solid-state DSSC generally employ Au as counter electrode. Although the cost of DSSC is lower than the Si-based solar cell, the novel mental is still an issue for further dcreasing the price of DSSC. So, their will be a critical improvement if the novel mental counter electrode could be replaced by other cheap material. Thus, the DSSC will turn into low-cost photovoltaic devices in the real sence.Inorder to avoid the disadvantages of the novol mental counter electrode such as high-price and complicated preparation process. In this paper, we exploed a series counter electrodes based on organic polymer (PEDOT), inorganic compound (NiS) and carbon (C) materials, and then applied in mesoscopic DSSC with different electrolyte. Moreover, we optimized the performace of these mesoscopic DSSC by adjusting the structure and preparation process. The employment of the counter electrods without novel mental provides a feasible view for the future development of low-cost mesoscopic DSSC. The main contents of this paper include: Firstly, We prepaed PEDOT counter electrods with high catalytic activity by electropolymerization method. The thickness of these PEDOT films can be adjusted by controlling the polymerization charge. EIS and CV measurement indicated that the more polymerization charge of the PEDOT film result in higher catalytic activity to the iodide/triiodide redox couple. After optimization, the PCE of mesoscopic DSSC based on the PEDOT200mC counter electrode reached7.60%, which is comparable to the Pt version.Secondly, We applied mesoporous TiO2layer as a scaffold, and deposited PEDOT into the mesoporous TiO2layer to prepare a new kind of PEDOT/TiO2composite electrode. EIS measurement showed this PEDOT/TiO2composite electrode possessed higher catalytic activity than the pure PEDOT electrode in inorganic sulfur electrolyte. Besides, an electrochemical method was used to prepare CdS quantum dot, which showed much better than the common used sequential ironic adsorption reaction method. Finally, the PCE of the CdS quantum dot DSSC based on PEDOT/TiO2composite electrode reached1.87%.Thirdly, Due to the thickness of the PEDOT films can be adjusted by changing the polymerization charge, we developed a new kind of transparent PEDOT electrode by using Bis-EDOT as the polymerization agent. UV-visiable light absorbtion measurement showd the transparency of this PEDOT electrode reached a high value up to90%. Furthermore, this transparent PEDOT electrode possessed favorable catalytic activity to the organic sulfur redox couple (AT/BAT). Bifacial mesoscopic DSSC based on this transparent PEDOT electrode possessed rear-side PCE of4.35%, which is70%of the front-side PCE.Fourthly, Transparent NiS electrode with high catalytic activity was prepared by a new power pulse electrodeposition method with different periodic values. SEM and EDS measurement showed that the particle size and the atom ratio of the NiS crystal can be change by the value of period. Moreover, the larger ratio of S atom in the NiS crystal make the electrode possessed higher catalytic activity to ET/BET redox couple. Finally, bifacial mesoscopic DSSC based on this transparent NiS electrode possessed rear-side PCE of4.98%, which is78%of the front-side PCE.Fifthly, Carbon material was firstly introduced in the perovskite-based mesoscopic solar cell. We fabricated monolithic heterojunction based on TiO2/CH3NH3PbI3with carbon counter electrode. Upon optimizing the device structure and the carbon electrode, we obtained mesoscopic perovskite solar cell with PCE of6.64%. Furthermore, TiO2nanosheets was synthesized and used as the host of CH3NH3PbI3to replace TiO2nanoparticles. EIS measurement showed that, compared to TiO2nanoparticles, this2-D TiO2nanocrystalline possessed lower recombination at the interface of TiO2/CH3NHsPbI3. Indeed these TiO2nanosheets enhanced the performance of the monolithic mesoscopic solar cells based on perovskite. As a result a PCE up to9.65%was obtained.