Investigation of photosensitive and photodetector characteristics of n-TPA-IFA/p-Si heterojunction structure

n-TPA-IFA organic material was synthesized and deposited on p-Si by spin coating method to produce n-TPA-IFA/p-Si heterojunction diode. We determined that the dielectric constant and energy band gap of TPA-IFA organic material were 3.91 and 3.37 eV by DFT/B3LYP/6-311G(d,p) method using on Gaussian 09 W, respectively and the carrier type of TPA-IFA organic semiconductor material was also n-type at room temperature from temperature-dependent hall effect measurements. Using forward and reverse bias I-V measurements in the dark and under various light intensities, we examined the key electrical characteristics of the n-TPA-IFA/p-Si heterojunction diodeincluding, Qb and n. It was determined that the rectification ratio (RR) was approximately 104. The reverse current's observed increasing behavior with increasing light indicates that the produced heterojunction diode can be utilized as a photo-diode, detector, or sensor. The photodetector properties of n-TPA-IFA/p-Si heterostructure were explored at different light intensities, and the photoresponsivity (R), photosensitivity (PS), specific detectivity (D), and linear dynamic range (LDR) of the heterojunction found to be changed with reverse voltage and light intensity. It was found that as light intensity increased, the linear dynamic range (LDR), a crucial characteristic for image sensors, increased as well (10.15 dB and 18.84 dB for 20 and 100 mW/cm2). Ultimately, the findings confirmed that the TPA-IFA-based heterojunction diode could be obtained for the photodetector application.Comment: 24 pages, 15 figures, Submitted to Journal of Materials Science: Materials in Electronic

Design, synthesis and theoretical simulations of novel spiroindane-based enamines as p-type semiconductors

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Characterisation and optimisation of hybrid polymer/metal oxide photovoltaic devices

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Low-Molecular Weight Molecules as Selective Contacts for Perovskite Solar Cells

La tecnologia fotovoltaica és una de les fonts d'energia neta i renovable més prometedores per reduir l'impacte ambiental dels combustibles fòssils en les últimes dècades. en aquest context, les perovskites són un material que ha atret recentment una atenció important a causa de la seva capacitat per aconseguir eficiències de conversió molt elevades. Les capes de càrrega selectiva juguen un paper crucial en el ràpid augment del rendiment del dispositiu i en l'estabilitat de les cel·les solars de perovskita. Recentment, l'aplicació de mono-capes auto-assemblades formades per molècules orgàniques que funcionen com a capes selectives de càrrega en cel·les solars de perovskita ha atret una gran atenció a causa d'avantatges com la rendibilitat, l'estabilitat i l'absència d'additius. L'objectiu d'aquesta tesi és el disseny i la síntesi de noves molècules que formen mono-capes auto-assemblades que funcionin com a capes selectives de forats en cel·les solars de perovskita per aconseguir una eficiència de conversió d'alta d'energia i una vida d'envelliment d'alt rendiment feta a mida.La tecnología fotovoltaica es una de las fuentes de energía limpia y renovable más prometedoras para reducir el impacto ambiental de los combustibles fósiles en las últimas décadas. en este contexto, las *perovskites son un material que ha atraído recientemente una atención importante a causa de su capacidad para conseguir eficiencias de conversión muy elevadas. Las capas de carga selectiva juegan un papel crucial en el rápido aumento del rendimiento del dispositivo y en la estabilidad de las celdas solares de *perovskita. Recientemente, la aplicación de *mono-capes auto-asemejadas formadas por moléculas orgánicas que funcionan como capas selectivas de carga en celdas solares de *perovskita ha atraído una gran atención a causa de ventajas como la rentabilidad, la estabilidad y la ausencia de aditivos. El objetivo de esta tesis es el diseño y la síntesis de nuevas moléculas que forman *mono-capes auto-asemejadas que funcionen como capas selectivas de agujeros en celdas solares de *perovskita para conseguir una eficiencia de conversión de alta de energía y una vida de envejecimiento de alto rendimiento hecha a medida.Photovoltaic technology is one of the most promising clean and renewable energy sources to reduce the environmental impact of fossil fuels in recent decades. In this context, perovskites are a material that has recently attracted significant attention due to their ability to achieve very high conversion efficiencys. Selective charge layers play a crucial role in rapidly increasing device performance and in the stability of perovskite solar cells. Recently, the application of self-assembly mono-caps made up of organic molecules that function as selective layers of charge in solar perovskite cells has attracted great attention due to advantages such as profitability, stability and the absence of additives. The goal of this thesis is the design and synthesis of new molecules that form self-assembly mono-layers that function as selective layers of holes in solar perovskite cells to achieve high-energy conversion efficiency and a high-performance aging life tailored to size

Molecularly Engineered Hole Transporting Materials for High Performance Perovskite Solar Cells

Perovskite solar cells have rapidly revolutionized the photovoltaic research showing an im-pressively dynamic progress on power conversion efficiency from 3.8 to 22% in only several years, a record for a nascent technology. Furthermore, inexpensive precursors and simple fabrication methods of perovskite materials hold a great potential for future low-cost energy generation enabling the global transition to a low-carbon society. The best performing device configuration of perovskite solar cell is composed of an electron transporting material, typi-cally a mesoporous layer of titanium dioxide, which is infiltrated with perovskite material and coated with a hole transporting material. However, although perovskite solar cells have achieved high power conversion efficiency values, there are several challenges limiting the industrial realization of low-cost, stable, and high-efficiency photovoltaic devices. To date, spiro-OMeTAD and PTAA are hole transporting materials of choice in order to main-tain the highest efficiency, however, the prohibitively high price hinders progress towards cheap perovskite solar cell manufacturing and may contribute to more than 30% of the overall module cost. Additionally, such wide bandgap hole transporting materials typically require doping in order to match necessary electrical conductivity and the use of additives is prob-lematic, since hygroscopic nature of doping makes the hole transporting layer highly hydro-philic leading to rapid degradation, negatively influencing the stability of the entire device. In order to overcome these problems, the rational design, synthesis, and characterization of a variety of small molecule-based hole transporting materials have been on a focus of this the-sis. Through judicious molecular engineering four innovative hole transporting materials KR131, KR216, KR374, and DDOF were developed via alternative synthetic schemes with the minimized number of steps and simple workup procedures allowing cost-effective upscale. Employing various characterization methods, the relationship between the molecular struc-ture of the novel hole transporting materials and performance of perovskite solar cells was investigated, leading to a fundamental understanding of the requirements of the hole trans-porting materials and further improvement of the photovoltaic performance. Furthermore, the synthesis of the dopant-free hole transporting materials based on push-pull architecture is presented. Highly ordered characteristic face-on organization of KR321 hole transporting molecules benefits to increased vertical charge carrier transport within a perov-skite solar cell, leading to a power conversion efficiency over 19% with improved durability. The obtained result using pristine hole transporting material is the highest and outperforms most of the other dopant-free hole transporting materials reported to date. Highly hydropho-bic nature of KR321 may serve as a protection of perovskite layer from the moisture and pre-vent the diffusion of external moieties, showing a promising avenue to stabilize perovskite solar cells

Dendritic poly(3-hexylthiophene) star copolymer systems for next generation bulk heterojunction organic photovoltaic cells

Philosophiae Doctor - PhDThe continuous increase in energy consumption and decrease in fossil fuels reserves are a primary concern worldwide; especially for South Africa. Therefore, there is an urgent need for alternative energy resources that will be sustainable, and environmentally friendly in order to tackle the ecological degradation generated by the use of fossil fuels. Among many energy ‘niches’, solar energy appears to be one of the most promising and reliable for the African continent because of the constant availability of sun light. Organic conjugated polymers have been identified as suitable materials to ensure proper design and fabrication of flexible, easy to process and cost-effective solar cells. Their tendency to exhibit good semiconducting properties and their capability to absorb photons from the sunlight and convert it into electrical energy are important features that justify their use in organic photovoltaic cells. Many different polymers have been investigated as either electron donating or electron accepting materials. Among them, poly(3-hexylthiophene) is one of the best electron donor materials that have been used in organic photovoltaic cells. It is a good light absorber and its Highest Occupied Molecular Orbital (HOMO) energy level is suitable to allow electron transfer into an appropriate electron acceptor. On the other hand, the molecular ordering found in dendrimers attracted some interest in the field of photovoltaics as this feature can ensure a constant flow of charges. In this work, I hereby report for the first time, the chemical synthesis of a highly crystalline dendritic star copolymer generation 1 poly(propylene thiophenoimine)-co-poly(3-hexylthiophene) (G1PPT-co-P3HT) with high molecular weight and investigate its application as donating material in bulk heterojunction organic photovoltaics

Photoelectrical and photoelectrochemical characterization of the materials used in dye-sensitized and perovskite solar cells.

Solar energy is one of the most important alternative renewable energy sources to fulfill the increasing demand of energy in the world. Third-generation solar cells like dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic solar cells are extensively studied to increase their photoconversion efficiency, and ultimately for their large-scale implementation. A dye-sensitized solar cell consists of a photoanode of a mesoporous film of titania sensitized with dye sandwiched with a counter electrode, which is usually a platinum-coated transparent conducting oxide, and a redox couple injected between the photoanode and counter electrode. Doping titania with rare-earth metal oxides (REOs) has been an interesting approach to improve the conversion efficiency of dye-sensitized solar cells. REOs have been doped into titania paste to show an improvement in the photovoltaic performance of dye-sensitized solar cells, however, most of the reported cells are not efficient enough to conclude whether the enhancement is due to doping or it is because of the cell quality. We incorporated nanoparticles (NPs) of REOs in titania paste and built highly reproducible dye-sensitized solar cells using amphiphilic C101 dye and iodide/triiodide redox couple in nitrile-based solvent (Z960 electrolyte). The doping level for optimized cells was 2.0 % for neodymium oxide and 1.0 % for erbium oxide. We did the measurements of photocurrent, impedance, incident photon-to-electron conversion efficiency (IPCE), and dye loading to investigate the mechanism of enhancement of the photovoltaic performance by REO NPs. Electrochemical impedance spectroscopy measurements showed that doping with REO decreased the total impedance of the cell and IPCE measurements revealed enhanced photon absorption by the dye in REO-doped cells. In the same fashion, the REO-doped anodes showed larger dye loading compared to undoped anodes, which was maximum for 1.0 % doping of erbium oxide and 2.0 % doping of neodymium oxide. REOs not only enhance dye adsorption but also facilitate electron transport through the mesoporous layer, thereby increasing the collection efficiency of the photoexcited electrons. To further explore the mechanism for the interaction between REO NPs and titania, an electrical and electrochemical study of REO-doped nanostructured titania films was performed. Doped films were found to be 40-50 times more conductive than undoped films, with linear current-voltage characteristics. Cyclic voltammograms of doped samples showed an enhanced scan rate dependence in the deep trap regime due to a slower charge trapping rate. Finally, electrochemical impedance measurements revealed a decrease in space charge density and a shift in the flat-band potential. Taken together, these results suggest that charge transfer from the REO neutralizes the deep trap states in the nanostructured titanium dioxide (NTD) film, decreasing charge scattering, and improving the NTD performance as an electron acceptor and electron transport material. Perovskite solar cells (PSCs) were first made when the dye-loaded semiconductor of dye-sensitized solar cell was replaced by perovskite layer and liquid electrolyte by a hole transport layer. The light harvesting perovskite layer is sandwiched between electron-transport and hole transport layers. Organic-inorganic perovskites, also known as hybrid perovskites have fascinating optoelectronic properties for their applications in highly efficient solar cells. The stability in ambient conditions and hysteresis in current-potential curves are two main challenges. The ease with which the separation of photogenerated charge carriers, electron-hole pairs (excitons), takes place is very critical for the performance of PSCs. In addition to the work function difference of electron-transport and hole transport layers, the intrinsic built-in potential in the perovskite films can play a significant role in the separation of these excitons. The internal electric originates from the local polarization of the film due to non-centrosymmetric lattice and ionic polarization and can be measured through an AC photocurrent technique. The polarization of a pristine sample is strongly dependent on the size of grains and can be used to determine the quality of the film. After poling the film by applying a potential through interdigitated Au electrodes, the devices with different grain sizes behaved differently upon relaxation. We observed that the polarization of a mixed halide hybrid perovskite film strongly depends on the background environment. The Quartz Crystal Microbalance measurements reveal that the perovskite film adsorbs Ar gas in the presence of solar light. The combination of Ar gas and solar illumination results in the enhancement of the electric polarization of the mixed halide hybrid perovskite film. Consequently, the photocurrent is increased due to the stronger driving force for the separation of excitons. This observation is illustrated in an actual PSC where the photovoltaic enhancement is observed with Ar gas. Our results suggest that the contribution from the background environment should be taken into consideration when describing the photovoltaic performance of a PSC

New Strategies for Defect Passivation in High-Efficiency Perovskite Solar Cells

Lead halide perovskite solar cells now show excellent efficiencies and encouraging levels of stability. Further improvements in performance require better control of the trap states which are considered to be associated with vacancies and defects at crystallite surfaces. Herein, a reflection on the ways in which these traps can be mitigated is presented by improving the quality of the perovskite layer and interfaces in fully assembled device configurations. In this review, the most recent design strategies reported in the literature, which have been explored to tune grain orientation, to passivate defects, and to improve charge-carrier lifetimes, are presented. Specifically, the advances made with single-cation, mixed-cation and/or mixed-halide, and 3D/2D bilayer-based light absorbers are discussed. The interfacial, compositional, and band alignment engineering along with their consequent effects on the open-circuit voltage, power conversion efficiency, and stability are a particular focus