A Route to Fabricate Rapid and Efficient Dye-sensitized Solar Cells through Minimizing the Duration of TiO2 Film Disposition and Dye Sensitization

Dye Sensitized Solar Cell (DSSC) technology is considered a promising substitute to the conventional silicon-based solar cells due to DSSC’s low material cost, ease of fabrication, low toxicity, and relatively high power conversion efficiencies. The two major steps of DSSC fabrication are: 1) formation of a mesoporous TiO2 layer on a transparent conductive oxide (TCO) coated glass substrate to make its photoanode, and 2) sensitization of the photo-anode with dye. Conventionally, photoanodes are prepared by depositing a mesoporous TiO2 layer on a TCO-coated glass substrate and sintering at a high temperature (~450 °C) for 30-60 minutes. The prepared TiO2 is then dip-coated in a dye solution for ~24 hrs. These processes have remained unchanged for almost 27 years and require more than 90% fabrication time of a typical DSSC. Thus, they limit the throughput and cost-effectiveness of this technology. This thesis introduces a novel technique to rapidly form mesoporous TiO2 films on FTO (fluorine doped tin oxide)- coated glass substrates using microwave irradiation with essentially identical performance as conventional heating. Microwave (MW) assisted films were prepared at low temperatures (\u3c 260 °C) within less than 10 minutes. DSSCs fabricated with 8 minutes of MW irradiated films show similar efficiencies with that of conventionally fabricated DSSCs. Besides saving time, and energy compared to its counterpart, this approach may pave the way of plastic-based electronics. This thesis also demonstrates the rapid (\u3c 30 minutes) loading of two Functionalized Carboxylate Deposition (FCD) dyes through high vacuum (0.1 mTorr) FCD. The power conversion efficiency (PCE) achieved with the FCD DSSCs were higher than dip-coated DSSCs. Combinedly, microwaveassisted photoanode preparation, and FCD dye-sensitization can save more than 90% fabrication time for future ultra-low cost DSSCs

Functionalized Carboxylate Deposition of Triphenylamine-based Organic Dyes for Efficient Dye-sensitized Solar Cells

he standard dip-coating dye-loading technique for dye-sensitized solar cells (DSSCs) remains essentially unchanged since modern DSSCs were introduced in 1991. This technique constitutes up to 80% of the DSSC fabrication time. Dip-coating of DSSC dyes not only costs time, but also generates a large amount of dye waste, necessitates use of organic solvents, requires sensitization under dark conditions, and often results in inefficient sensitization. Functionalized Carboxylate Deposition (FCD) was introduced as an alternative dye deposition technique, requiring only 2% of the fabrication time, eliminating the need for solvents, and significantly reducing dye waste. In this study, FCD was used to deposit two relatively large triphenylamine-based organic dyes (L1 and L2). These dyes were sublimated and deposited in \u3c20 minutes via a customized FCD instrument using a vacuum of ∼0.1 mTorr and temperatures ≤280 °C. FCD-based DSSCs showed better efficiency (i.e., 5.03% and 5.46% for L1 and L2 dyes, respectively) compared to dip-coating (i.e., 4.36% and 5.35% for L1 and L2, respectively) in a fraction of the deposition time. With multiple advantages over dip-coating, FCD was shown to be a viable alternative for future ultra-low cost DSSC production

Rapid and Low-Temperature Processing of Mesoporous and Nanocrystalline TiO2 Film Using Microwave Irradiation

Nanoporous (np)-TiO2 films have multiple applications, including dye-sensitized and perovskite solar cells. However, preparation of np-TiO2 films on transparent conductive oxide-coated surfaces (e.g., fluorine doped tin oxide (FTO)) requires high-temperature sintering (450–500 °C) for at least 30–60 min in a conventional oven. Here, we introduce a novel technique to rapidly produce np-TiO2 films on FTO-coated glass substrates via microwave (MW) irradiation. np-TiO2 films were sintered on FTO-glass substrates in less than 10 min at temperatures less than 260 °C using an optimized MW irradiation program and a simple MW attenuation technique. Significantly, cracking of FTO-coated glass substrates was avoided during MW irradiation, which was a limiting problem in previous studies. MW-developed films were evaluated with UV–vis absorption spectrophotometry, Raman spectroscopy, X-ray diffraction, and atomic force microscopy, with MW-developed films ( \u3e4 min) producing essentially identical characteristics as conventionally annealed films. Dye-sensitized solar cells (DSSCs) fabricated with MW-developed films (8 min) demonstrated an overall power conversion efficiency of 7.16% as compared to 7.04% for conventionally-fabricated DSSCs. This rapid and low-temperature sintering technique saves time and energy and may also pave the way for deposition of np-TiO2 films on plastic-based substrates