Facile Solution Dropping Method for Dyeing TiO2 Electrode of Dye Sensitized Solar Cells (DSSCs) with Enhanced Power Conversion Efficiency and the Effects of New Metal Chelates as Additives for Perovskite Solar Cells (PSCs)

• Main Authors: Shih-Chieh Yeh, 葉世傑
• Other Authors: 鄭如忠
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/8cgf4n

博士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 106 === A simple solution dropping method was established for sensitizing TiO2 in the fabrication of dye-sensitized solar cells (DSSCs). Comparing with conventional solution dipping (or immersion) method, solution dropping method is very fast, less than ~5 minutes vs >2~24 hours typically required in solution dipping method. There are much less organic solvent and dye substance (95% less) used in the dyeing TiO2 process and hence significantly less disposal of chemical waste from the device fabrication. Therefore, our facile and very fast solution dropping method is a greener and more sustainable process than conventional dropping method. Moreover, the solution dropping method is superior to solution dipping method in terms of power conversion efficiency (PCE) of the device. We have acquired compelling evidences, dye uptake assessment of TiO2 electrode, depth profile assay by SEM-EDX, and charge dynamic characteristics from transient photocurrent/photovoltage analysis, indicating the elevated dye loading of TiO2 electrode is the main cause of increasing short-circuit current and hence the PCE of DSCs. Three types of dye were used in this study to demonstrate the superiority of solution dropping method. They are classical N719 (ruthenium transition metal complex), 1P-PSS (metal free organic dye), and the newly synthesized ATT (a -pyrrole carbon-conjugated zinc tetraphenylporphyrin). With solution dropping method, the average PCEs (from thirty or forty tested devices of each dye) are all improved, 8.1% to 8.5%, 5.9% to 6.6%, and 4.1% to 6.7% for N719, 1P-PSS, and ATT, respectively. Further more, high performance 2,6-subsititute BODIPYs were also developed by solution dropping method. The best PCE of MPBTTCA could be achieved to 6.4%. Especially for the PCE of MPBT-pyO device by dropping method was ten times higher than it by dipping method. This indicates the new solution dropping method could be a feasible method for all dying process. On the other hand, the incorporation of additives to perovskite layers is one of the most effective strategies to optimize perovskite solar cells (PSCs). Herein, we developed a series of 8-methyl-1,5-naphtyridin-4-ol (HmND) metal chelates as additives for both regular (mesoporous TiO2-based) and inverted (nickel oxide; NiOx-based) PSCs. These metal chelate additives including Zn(II), Mg(II), Al(III), Ga(III), In(III), and Hf(IV) metal cations, and the free ligand HmND were respectively incorporated into CH3NH3PbI3 films by a two-step method. The interaction of naphtyridine on metal chelates with lead and iodine ions in DMSO solution was first investigated by 1H-NMR and photoluminescence (PL) spectra. Moreover, the morphology of CH3NH3PbI3 affected by the chemical structure of metal chelates was investigated by field emission scanning electron microscopy (FE-SEM). A featureless morphology was found for the pristine CH3NH3PbI3 films. For the films incorporated with metal chelates, leaf-like or rose petal-like morphologies were observed on mesoporousTiO2 scaffold substrates, whereas coral reef-like morphologies were found on NiOx substrates. Apart from that, HOMO level shifts and microstructure phases of these modified CH3NH3PbI3 films were also thoroughly investigated. These metal chelate-based PSCs exhibited a significant enhancement in open-circuit voltage (VOC) (maximum 1.06 V vs 0.94 V for the pristine sample). The maximum power conversion efficiency (PCEmax) of Mg chelate-based devices were 12.12% and 14.54% for regular and inverted PSCs, respectively. In addition, the charge transport properties of metal chelate-based devices were evaluated by space-charge-limited-current (SCLC) method. To understand the long-term stability of respective metal chelate-based devices, these photovoltaic parameters were recorded for 350 h. The facial form in chelate-based solar cells were able to exhibit 12% of PCE increase when compared to their original values.