İndolin ve benzotiyadiazol esaslı boyaların güneş hücrelerinde kullanımlarının incelenmesi = Investigation of the uses of indoline andbenzothiadiazole based dyes in sun cells

Abstract

Gratzel ve grubu tarafından 1991 yılında keşfedilen, çevre dostu, ucuz, üstün molar absorptivitesi olan, yüksek dönüşüm verimliliğine sahip boya duyarlı güneş pilleri (BDGH' ler), fotovoltaik alan için umut verici bir alternatiftir. BDGH' ler beş ana bileşenden oluşur: (i) iletken bir cam substrat, (ii) TiO2 gibi bir yarı iletken, (iii) hassaslaştırıcı boya, (iv) platinleştirilmiş bir karşı elektrot ve (v) redoks çifti içeren bir elektrolit. Bahsedilen bileşenlerin kombinasyonu, bu güneş pillerinin performansını önemli ölçüde etkiler. Hassaslaştırıcı boyanın adsorbe edildiği yarı iletken TiO2 filmi, güneş ışığı altında uyarılan elektronların taşınması için bir yol görevi görür. Ayrıca boya adsorpsiyonu, ışık saçılımı ve elektron taşıma özelliklerinde etkili olan TiO2 filminin morfolojisi ve yapısı, güneş ışığının elektrik enerjisine dönüşüm verimi için oldukça önemlidir. Fotoanot için solvent ve daldırma süresi de BDGH' lerin fotovoltaik performansını etkileyen önemli faktörlerdir. Ortak duyarlılaştırma (co-sensitization) yaklaşımı, BDGH' lerde hasat elde etmek için oldukça tercih edilen başka bir yöntemdir. Bu yaklaşım, her bir hassaslaştırıcının dar spektral aralığının sınırlandırılmasının üstesinden gelerek BDGH' nin spektral absorpsiyon aralığını geliştirir, böylece güneş pillerinin ışık toplama etkinliğini arttırır. Benzotiadiazol (RK1) ve indolin (D205) dahil olmak üzere metal içermeyen boyalara dayalı boya duyarlı güneş pillerinin (BDGH' ler) üretimi, TiO2 bileşimi, çözücü tipi, duyarlılaştırma süresi, yardımcı adsorban kullanımı ve ortak duyarlılaştırma açısından optimize edildi. Metanol ve tetrahidrofuranın, sırasıyla RK1 ve D205' e dayalı BDGH' leri imal etmek için en uygun çözücüler olduğu bulundu. Optimize edilmiş koşullar altında, saydam/şeffaf ve saçılan TiO2 fotoanot karışımından yapılan D205 tabanlı BDGH, %5,76 'lık bir güç dönüşüm verimliliği (PCE) sergilerken, şeffaf/saçılan TiO2' ye sahip RK1 tabanlı BDGH, %8,43' lük bir PCE elde edildi. Her boya için farklı fotoanot bileşimlerinin kullanılması, bu boyaların boyut veya geometrisindeki farklılık ile açıklanabilir. BDGH' lerin performansını iyileştirmek için kademeli bir ortak duyarlılaştırma stratejisi uygulandı. İki boyaya dayalı ortak duyarlılaştırılmış güneş pili, 360-670 nm aralığında pankromatik bir spektral tepki gösterir ve RK1 ile duyarlılaştırılmış güneş pillerinden daha üstün olan %9,30' luk bir genel PCE gösterdi.

The energy crisis is one of the most important challenges humanity has faced in recent times. Renewable energy, which mainly includes solar energy, tidal energy and wind energy, has become an indispensable solution for the energy demands of the future. Among the different types of renewable energy, solar energy is the most important because of its zero pollution, no resource requirement and economic features. Renewable energy offers significant advantages over conventional energy sources and is plentiful. The sun reaches the earth's surface 1000 times more energy than all fossil fuels consumed today. The average amount of solar energy taken into the Earth's atmosphere is about 342 W m-2 and 30% of this is scattered or reflected back to space, leaving 70% (239 W m2) of harvest so that it can be used for energy purposes. A photovoltaic cell (PV) converts solar radiation directly into electrical energy. First generation photovoltaic batteries are plate based. It built on techniques already used for integrated circuit fabrication at the time, allowing them to leverage their expertise in much silicon wafer fabrication. The first generation of photovoltaic modules is still the most common, accounting for 95% of the power produced in 2020. Second generation cells have been developed with the aim of reducing the costs and improving the properties of the previous generation. A good criterion to maintain in the manufacture of photovoltaic modules is that the total cost of the module is half the cost of installation and the cost of the cells is likewise less than half of the module. The way to get a cheaper module is to reduce the cells' high material demand and the associated inherent cost. Second generation cells are based on thin absorbent film technology. It is a few μm thick instead of 100–200 μm of the previous generation. However, there has been a decrease in productivity. Third-generation solar cells are defined as devices that convert photons into electricity with a cheaper production cost and high efficiency. Solar cells based on pure Si forms were first generation devices with ~27% efficiency. Because of the high cost of manufacture, researchers sought new processes and materials that led to second-generation solar cells, which included copper indium diselenide, amorphous silicon, and polycrystalline solar cells. Production was expensive, as the manufacturing process required a large amount of energy. The third generation solar cell is cheaper to manufacture and the cells are highly efficient. As third-generation solar cells, dye-sensitized solar cells are currently of scientific and technological interest because they are a highly efficient, simple to manufacture, and low-cost alternative to conventional photovoltaic devices. A typical BDGH usually consists of photo-anode, counter electrode, electrolyte and photosensitizer. xxii BDGHs are excited by the sensitizing (dyed) light on the device and inject electrons into the conduction band of the metal oxide. Electrons reach the conductive substrate from the metal oxide film and flow through an external circuit to the counter. At the counter electrode, the oxidized component of the redox couple (electrolyte) is reduced and the oxidized form of the dye is finally regenerated by the reduced component of the redox. All components of BDGH play an important role in achieving the promising photo-conversion efficiencies of solar cells. Among these components, the photoanode contributes significantly to the transport of the photo-excited electron from the dye to the external electrical circuit. Generally, wide bandgap semiconductor metal oxides (eg ZnO, TiO2, etc.) are deposited on a transparent conductive substrate to prepare the photoanodes. The performance of photoanodes depends on the band gap, morphology, composition of the metal oxides and the thickness of the metal oxide layers. The working electrode is defined in the BDGH system as a porous TiO2 film that provides a large surface area for chemical absorption of the dye on the electrode surface. As defined from various literatures, an efficient electron transport layer (i.e. metal oxide layer) should (1) have a high surface area to increase effective light harvesting and dye loading, (2) be transparent to visible light to minimize photon loss, (3 ) the conduction band must be sufficiently below the lowest unoccupied molecular orbitals (LUMOs) of the dye to allow adequate injection of photo-generated electrons, (4) must have high electron mobility for efficient electron transport, (5) redox to reduce the electron recombination rate and (6) contain hydroxyl groups to bind the dye molecules to its surface. In BDGH, the dye acts as a photosensitizer, usually fixed on the metal oxide surface. In the presence of sunlight, the dye absorbs the photon and creates light-excited electrons. Photo-excited electrons are injected into the conduction band of semiconductor metal oxides. The electrolyte is an essential component of all dye-sensitized solar cells. They act as charge carriers that collect electrons at the cathode and transport the electrons back to the dye molecule. In terms of cell efficiency, the most commonly used electrolyte is the iodide/triiodide (I-/I3-) redox couple in an organic matrix, usually acetonitrile. Within the scope of the thesis, it is aimed to investigate the use of two metal-free synthetic organic compounds based on indoline (D205) and benzothiadiazole (RK1) as sensitizers in dye-sensitized solar cells. Both D205 and RK1 are compounds that have been the subject of many scientific studies separately. However, there is no study in the literature examining both together. Compound D205 was chosen because of its properties such as not being aggregate and showing absorption at long wavelengths. RK1 dye has been included in the thesis because it is known that it has photovoltaic performance superior to most organic compounds. The optical and electrochemical properties of these two dyes and the photovoltaic properties of the solar cells to be manufactured from these dyes were investigated. In addition to examining the properties of these two dyes separately, devices in which both are used as sensitizers were obtained. In this way, it is aimed to increase the existing conversion efficiency by performing the common sensitization process. In addition, some properties of the semiconductor (TiO2) such as particle size and thickness on the conductive glass are also extremely important. For this reason, it has been ensured to increase the efficiency by using semiconductor pastes with different structures. The production of dye-sensitized solar cells (BDGHs) based on metal-free dyes, including benzothiadiazole (RK1) and indoline (D205), was optimized in terms of TiO2 composition, solvent type, sensitization time, co-adsorbent usage, and co-sensitization. Methanol and tetrahydrofuran were found to be the most suitable solvents for fabricating RK1-based and D205-based BDGHs, respectively. Under optimized conditions, the D205-based BDGH, employing a combination of clear/transparent and scattering TiO2 photoanodes, achieved a power conversion efficiency (PCE) of 5.76%, while the RK1-based BDGH with transparent/scattered TiO2 demonstrated a PCE of 8.43%. The use of different photoanode compositions for each dye can be attributed to the disparity in size or geometry of these dyes.