Tandem solar cells are potentially much more efficient than the silicon solar cells that currently dominate the market but require materials with different bandgaps. This thesis presents work on silicon nanocrystals (Si-NC) embedded in silicon carbide (SiC), which are expected to have a higher bandgap than bulk Si due to quantum confinement, with a view to using them in the top cell of a tandem cell. The strong photoluminescence (PL) of precursor films used to prepare Si-NC in SiC (Si-NC/SiC) was markedly reduced upon Si-NC formation due to simultaneous out-diffusion of hydrogen that passivated dangling bonds. This cannot be reversed by hydrogenation and leads to weak PL that is due to, and limited by, non-paramagnetic defects, with an estimated quantum yield of ≤5×10^-7. Optical interference was identified as a substantial artefact and a method proposed to account for this. Majority carrier transport was found to be Ohmic at all temperatures for a wide range of samples. Hydrogenation decreases dangling bond density and increases conductivity up to 1000 times. The temperature-dependence of conductivity is best described by a combination of extended-state and variable-range hopping transport where the former takes place in the Si nanoclusters. Furthermore, n-type background doping by nitrogen and/or oxygen was identified. In the course of developing processing steps for Si-NC-based tandem cells, a capping layer was developed to prevent oxidation of Si-NC/SiC, and diffusion of boron and phosphorus in nanocrystalline SiC was found to occur via grain boundaries with an activation energy of 5.3±0.4 eV and 4.4±0.7 eV, respectively. Tandem cells with a Si-NC/SiC top cell and bulk Si bottom cell were prepared that exhibited open-circuit voltages V_oc of 900 mV and short-circuit current densities of 0.85 mAcm^-2. Performance was limited by photocurrent collection in the top cell; however, the V_oc obtained demonstrates tandem cell functionality.

Le dopage du silicium par implantation ionique pour le photovoltaïque est une application relativement récente dont l'essor se heurte encore aujourd'hui aux coûts élevés d'intégration au sein des lignes de fabrication des cellules solaires. L'implantation ionique par immersion plasma promet de répondre aux futures exigences du secteur en termes de coûts et de productivité.Ces travaux de thèse ont permis le développement de procédés d'implantation ionique par immersion plasma de l'équipement PULSION®, conçu par IBS, dédiés à la fabrication de cellules solaires en silicium monocristallin. Dans un premier temps, nous montrons qu'il permet la réalisation de profils de dopage d'émetteur de type n variés, répondant aux exigences des cellules solaires à haut rendement. Les émetteurs fabriqués sont caractérisés de manière chimique, physique et électrique afin de démontrer leur excellente qualité. L'intégration de l'implantation ionique des émetteurs au sein d'un processus de fabrication industriel et peu coûteux, développé par l'INES sur silicium monocristallin de type p, permet d'atteindre des rendements de conversion supérieurs à 19,3%, soit un gain de plus de 0,5% par rapport aux rendements obtenus avec des cellules usuelles à émetteurs dopés par diffusion POCl3.La réalisation d'émetteurs de type p est également étudiée dans ce mémoire afin de préparer la transition technologique vers les cellules solaires sur silicium monocristallin de type n. Confirmant les atouts et le potentiel de la technologie d'implantation ionique par immersion plasma, les travaux menés au cours de cette thèse débouchent sur la conception d'un prototype industriel PULSION® dédié au photovoltaïque. / Ion implantation is a major process technology for manufacturing integrated circuits. However, silicon doping by ion implantation for photovoltaics is a relatively recent application, and its growth still faces high costs of integration into solar cell production lines. Plasma-immersion ion implantation (PIII) promises to meet the future industry requirements in terms of costs and productivity.This thesis work has led to the development of processes dedicated to silicon-based solar cell manufacturing using the plasma-immersion ion implanter – PULSION® – designed by IBS. First, we show that PIII enables the realization of various doping profiles for phosphorus-doped emitters which fit the requirements of high-efficiency solar cells. Emitters thus fabricated are chemically, physically and electrically characterized to demonstrate their excellent quality. Those emitters, implanted through plasma immersion and integrated into a low cost solar cell manufacturing line from INES on monocrystalline silicon, enable to raise the conversion efficiency, obtained with conventional POCl3-diffused solar cells, by more than 0.5% absolute to reach efficiencies above 19.3%.Fabrication of p-type boron implanted emitters is also studied in order to improve conversion efficiencies of p-type silicon based solar cells, but also in order to anticipate the technological shift from p-type to n-type silicon material. Thanks to this thesis work, the strength and potential of PIII for photovoltaic applications have been proven and this has convinced IBS to design a PULSION® equipment dedicated to solar cell manufacturing.

Six peripherally meso-modified Zn (II) porphyrin sensitizer dyes are designed and their J-V performance in dye sensitized solar cell (DSSC) evaluated. Electron-donating groups including phenothiazine, carbazole and pyrene are used to modify the porphyrin macrocycle at the meso-carbon position(s). To compare the effect of donor substitution on the performance of the cells in terms of short circuit current (Jsc), light harvesting efficiency (LHE) and power conversion efficiency (η), two sets of sensitizers with different degrees of substitution are synthesized. One set of dyes (mono-substituted) have one electron donor at trans-position to the acceptor, while the second set (tri-substituted) dyes have three of the same type electron donor groups at 5, 10 and 15 meso-carbon positions making all the six dyes push-pull type sensitizers incorporating 4'-carboxyphenyl as an electron-acceptor/anchor group. Different spectroscopic and electrochemical methods are used to study the photophysical and electrochemical properties of the dyes, while the photovoltaic performance of their cells under 1.5 A.M is studied using solar simulator. Meso-substitution of Zinc (II) porphyrin with these small donor molecules is shown to improve the light harvesting character of the Zinc (II) porphyrin macrocycle in the UV-Vis absorption while at same time improving its fluorescence quantum yield, excited-state life time and electron donating potential. All these factors combined make these meso-modified dyes better sensitizers with suitable Δ0 Δ0, and much improved power conversion efficiencies (PCE) compared to unsubstituted Zn (II) porphyrin. In particular, as a result of the peripheral modification, a doubling in efficiency in the mono- substituted series (RA-200-Zn; η=^M 4.2%, Jsc= -13.13 mA cm-2, Voc=0.54 ) and tripling in the tri-substituted series ( tri-phenothiazine Zn (II) Porphyrin; η= 7.3%, Jsc= -18.15 mA cm-2, Voc= 0.55 ) compared to unsubstituted Zn (II) porphyrin (η= 2.11%, Jsc= -5.7 mA cm-2, Voc= 0.53 V) has been accomplished.

As células solares poliméricas (PSCs) e diodos emissores de luz poliméricos (PLEDs) destacam-se dos seus análogos inorgânicos pela possibilidade de reduzir custo de fabricação, obtenção de dispositivos mais leves e flexíveis, maior liberdade no design e menor tempo de produção de dispositivos, devido à sua maior facilidade de processamento. Neste trabalho foram investigadas as mudanças nas propriedades fotofísicas, eletroquímicas e elétricas do poli[2,7-(9,9-dioctilfluoreno)-alt-4,7-bis(2,5-tiofeno)-2,1,3-benzotiadiazol] (PDBT) e seus derivados contendo grupos substituintes hexila no anel tiofeno. Este polímero conjugado é conhecido por seu potencial para aplicações em PSCs. Para tanto, três copolímeros, contendo diferentes concentrações de mero tiofeno substituído, foram sintetizados via reação de acoplamento de Suzuki. Usando técnicas adequadas, foram verificadas correlações entre o comportamento fotofísico, térmico e elétrico dos copolímeros e o teor de tiofeno substituído. Os materiais poliméricos sintetizados foram aplicados como camada ativa em PLEDs e PSCs. Em relação aos PLEDs, foi verificada baixa luminância e emissão de luz na faixa da cor laranja e cor verde. Além disso, diferentes efeitos, relacionados com a concentração de tiofeno substituído e as propriedades fotovoltaicas, foram identificados nas PSCs montadas. / Polymer Solar cells (PSCs) and polymer light-emitting diodes (PLEDs) draw attention from their inorganic analogues for the possibility of manufacturing cost reduction, more light and flexible devices, as well as the greater design freedom and shorter production time devices due to its easier processing. In this work, we investigated the changes in the photophysical, electrochemical and electrical properties from poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(2,5-thiophene)-2,1,3-benzothiadiazole] (PDBT) that was caused by hexyl substituents introduction on the copolymer thiophene rings. This conjugated polymer system is known for its PSCs applications potential. Therefore, three copolymers, with different concentrations of substituted thiophene mere, were synthesized by Suzuki polycondensation. Using appropriate techniques, direct relationships were verified between the photophysical, thermal and electrical behavior from copolymers and substituted thiophene content. The synthesized polymeric materials were applied as active layer in PLEDs and PSCs. Regarding PLEDs, it was verified a low luminance and light emission in the range of orange and green colors. Furthermore, different effects, related to the substituted thiophene concentration and photovoltaic properties, were identified from mounted PSCs.

O objetivo do trabalho foi demonstrar que o polivinilcarbazol (PVK) dopado com Perclorato de Lítio (LiClO4) pode converter energia luminosa em energia elétrica. Esse material polimérico possui a propriedade de absorver e gerar pares de elétron-lacunas fornecendo uma corrente elétrica quando exposto à iluminação. Para essa finalidade foi construído um dispositivo (célula solar) com a seguinte estrutura: vidro / ITO / a-Si:H (p) / polímero PVK / µ-Si:H (n) / Al, tendo o PVK dopado como camada ativa. O estudo proposto, dessa maneira, teve como finalidade: pesquisar, desenvolver, fabricar e caracterizar esse dispositivo, analisando suas características elétricas e ópticas, sua eficiência de conversão (rendimento) e outros fatores relacionados ao seu desempenho e do processo de fabricação. / The objective of this article is to demonstrate that the Poly(N-vinylcarbazole) PVK dumped with lithium perchlorate (LiClO4) can transform solar energy to electrical energy. This polymer material has the property of absorbing and generate electron hole pairs, providing an electric current when exposed to enlightenment. To achieve that, a solar cell has been constructed with the follow structure: glass structure/ITO/a-Si:H (p)/polymer PVK/µ-Si:H (n)/Al, with the PVK working as active layer. This proposed article had the objective to research, develop, construct and characterize this device, analyzing its electrical and optical characteristics, efficiency and other topics related to its development and construction process.

As células solares poliméricas (PSCs) e diodos emissores de luz poliméricos (PLEDs) destacam-se dos seus análogos inorgânicos pela possibilidade de reduzir custo de fabricação, obtenção de dispositivos mais leves e flexíveis, maior liberdade no design e menor tempo de produção de dispositivos, devido à sua maior facilidade de processamento. Neste trabalho foram investigadas as mudanças nas propriedades fotofísicas, eletroquímicas e elétricas do poli[2,7-(9,9-dioctilfluoreno)-alt-4,7-bis(2,5-tiofeno)-2,1,3-benzotiadiazol] (PDBT) e seus derivados contendo grupos substituintes hexila no anel tiofeno. Este polímero conjugado é conhecido por seu potencial para aplicações em PSCs. Para tanto, três copolímeros, contendo diferentes concentrações de mero tiofeno substituído, foram sintetizados via reação de acoplamento de Suzuki. Usando técnicas adequadas, foram verificadas correlações entre o comportamento fotofísico, térmico e elétrico dos copolímeros e o teor de tiofeno substituído. Os materiais poliméricos sintetizados foram aplicados como camada ativa em PLEDs e PSCs. Em relação aos PLEDs, foi verificada baixa luminância e emissão de luz na faixa da cor laranja e cor verde. Além disso, diferentes efeitos, relacionados com a concentração de tiofeno substituído e as propriedades fotovoltaicas, foram identificados nas PSCs montadas. / Polymer Solar cells (PSCs) and polymer light-emitting diodes (PLEDs) draw attention from their inorganic analogues for the possibility of manufacturing cost reduction, more light and flexible devices, as well as the greater design freedom and shorter production time devices due to its easier processing. In this work, we investigated the changes in the photophysical, electrochemical and electrical properties from poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(2,5-thiophene)-2,1,3-benzothiadiazole] (PDBT) that was caused by hexyl substituents introduction on the copolymer thiophene rings. This conjugated polymer system is known for its PSCs applications potential. Therefore, three copolymers, with different concentrations of substituted thiophene mere, were synthesized by Suzuki polycondensation. Using appropriate techniques, direct relationships were verified between the photophysical, thermal and electrical behavior from copolymers and substituted thiophene content. The synthesized polymeric materials were applied as active layer in PLEDs and PSCs. Regarding PLEDs, it was verified a low luminance and light emission in the range of orange and green colors. Furthermore, different effects, related to the substituted thiophene concentration and photovoltaic properties, were identified from mounted PSCs.

O presente trabalho teve como objetivo a modelagem de células solares MOS operando em regime de inversão controlado por centros positivamente carregados na interface SiNxOy/Si. Este tipo de célula solar foi recentemente fabricada pela primeira vez no âmbito dos trabalhos desenvolvidos no grupo de Superfícies, Interfaces e Deposição Eletroquímica (GSIDE) do LSI/PSI/EPUSP utilizando dielétricos de porta ultra-finos (~2nm). A receita de crescimento de dielétrico ultra-fino desenvolvida foi no sentido de assegurar reprodutibilidade e uniformidade da espessura do dielétrico ao longo de áreas extensas de alguns cm2. Baseado nas curvas experimentais CxVg, GxVg e IxVg das células solares fabricadas, foi mostrado para as células fabricadas em substrato tipo P que existem os centros K predominantemente preenchidos com cargas positivas em todos os regimes de operação (acumulação, depleção e inversão). A densidade de cargas positivas (Qiq) na interface SiNxOy/Si além de ter resultado positivo, apresentou um comportamento linear com o potencial de superfície (ys) ou com a tensão de porta Vg de acordo com os resultados obtidos através de um simulador numérico desenvolvido para esta aplicação específica. Tal comportamento consistiu no acomodamento das cargas positivas na interface de forma que uma região de depleção profunda (Wd) é formada sem a presença da camada de inversão na condição sem iluminação. Para as células MOS submetidas a diferentes níveis de iluminação, tanto para os dielétricos crescidos a 850oC como também para aqueles que foram crescidos a 700oC, foi constatado que os centros K na interface funcionam como uma região de armazenamento de cargas positivas a medida em que os elétrons tunelam em direção à porta metálica da estrutura MOS. Como resultado, este tipo de comportamento significa uma nova forma de implementar o efeito fotovoltáico. / The goal of the present work was the modeling of MOS solar cells operating in an inversion regime controlled by positively charged centers at the SiNxOy interface. This type of solar cell was recently manufactured for the first time in the activities developed in the group of Surfaces, Interfaces and Electrochemical Deposition (GSIDE) from LSI/PSI/EPUSP using ultra-thin gate dielectrics (~2nm). The recipe for the growth of ultra-thin dielectrics was developed to ensure reproducibility and uniformity of the dielectrics thickness over large areas of few square centimeters. Based on the experimental curves CxVg, GxVg e IxVg of the manufactured MOS solar cells, it was shown for cells manufactured in P-type substrate that there are K centers dominantly filled with positive charges in all operating regimes (accumulation, depletion and inversion). The positive charge density (Qiq) at the SiNxOy/Si interface, in addition to having a positive charge, presented a linear behaviour with the surface potential (ys) or with the gate voltage (Vg) according to the results obtained from a numerical simulator developed for this application. Such behavior consisted of accommodating the positive charges at the SiNxOy/Si interface so that a deep depletion region (Wd) is formed without the presence of the inversion layer in the condition without illumination. For MOS cells subjected to different levels of illumination, both for dielectrics grown at 850oC as well as for those grown at 700oC, it was found that the K centers at the SiNxOy/Si interface work as a region of positive charge storage as the electrons tunnel from the interface towards the metal gate of the MOS cells. As a result, this type of behaviour means a new way of implementing the photovoltaic effect.

Le développement d'un colorant naturel sensibilisateur pour les applications de cellules solaires a attiré beaucoup d'attention en raison de ses avantages inhérents, tels que son faible coût, la préparation simple, les ressources facilement disponibles et le respect de l'environnement. Toutefois, les principaux problèmes liés à la cellule solaire sensibilisée par colorant (CSSC) sont une faible photostabilité et une faible efficacité. Dans cette thèse, la bixine extrait de graines de rocou (Bixa orellana L.) a été utilisée comme sensibilisateur. Pour améliorer sa stabilité et la performance des CSSC, l’utilisation de la kaolinite activée a également été étudiée. Une CSSC à haute efficacité nécessite une photo-électrode avec une grande surface spécifique pour adsorber efficacement le colorant. Ainsi le couple TiO2/kaolinite a été préparé dans ce but. Il est considéré que la kaolinite peut confiner la lumière incidente à l'intérieur de l'électrode et peut aussi améliorer la conduction d'électrons. Dans ce système, la kaolinite a également un rôle important pour accroître la photostabilité de la bixine. Un autre facteur affectant les performances des CSSC est le rôle important de l’électrolyte. Dans ces travaux, les carbonates organiques cycliques qui ont une constante diélectrique élevée et aussi un point d’ébullition élevé (plus de 300oC) ont été évalués comme solvants de l’électrolyte. Ces travaux ont été réalisés en quatre étapes: (1) extraction, purification et caractérisation de la bixine, (2) préparation, activation et caractérisation de la kaolinite, (3) étude d’adsorption de la bixine sur la surface de la kaolinite et du TiO2, et (4) fabrication des cellules solaires sensibilisées par la bixine (CSSB). Les résultats montrent que l’extraction accélérée par solvant en utilisant un mélange de 60% de cyclohexane et 40% d’acétone peut être une méthode d’extraction efficace pour la bixine. Après purification par la chromatographie flash, la bixine est isolée avec un dégré de pureté de 99,86%. Elle est composée de 88,11% de cis-bixine et 11,75% de dicis- bixine. L’activation par l’ammoniaque de la kaolinite calcinée (la métakaolinite) est une bonne méthode pour produire la kaolinite avec une très grande surface spécifique et un rapport Si/Al élevé. L’étude d’absorption de la bixine a montré que le carbonate de diméthyle est un solvant approprié pour la bixine. Il permet à la bixine un coefficient d’absorption élevé et de bonnes caractéristiques d’adsorption sur la surface de la photo-électrode. L’adsorption de monocouche de la bixine sur la surface de TiO2 ou la surface de la kaolinite est plus favorable pour obtenir un rendement énergétique plus élevée. La présence de la métakaolinite activée dans la photo-électrode TiO2 a contribué à améliorer les performances et la stabilité de la CSSB par rapport à la CSSB fabriquée avec la photoélectrode de TiO2 pur. Ces performances sont reproductibles. L’électrolyte exerce un effet synergétique avec la métakaolinite activée en faveur de l’amélioration des paramètres électriques de la CSSB. Sous une intensité lumineuse de 200 W/m2, la CSSB comprenant une photo-électrode de TiO2 modifié par 5% de métakaolinite activée et un système électrolyte de KiI/I2 dans l’acétate de carbonate de glycérol produit un rendement énergétique de (0,050+0,006)%, ce qui est plus élevé que celui de la CSSB comprenant une photo-électrode de TiO2 pur (0,027+0,012)%. L’utilisation d’un couple redox de LiI/I2 dans l’acétate de carbonate de glycérol produit le rendement maximum (0,086+0,014)%. La fonction de stockage et de chargement d’énergie des CSSB fonctionnent bien jusqu’au troisième jour de l’analyse. A ce jour, la CSSB fabriquée en utilisant la photoélectrode de TiO2 modifiée par la métakaolinite activée est 16 fois plus stable que celle de la CSSB fabriquée en utilisant la photo-électrode de TiO2 pur. / The development of natural dye sensitizer for solar cell applications has attracted much attention because of its inherent advantages such as low cost, simple preparation, readily available resources, and low impact in the environment. However, the main problems related to dye-sensitized solar cell (DCCS) are low photostability and low efficiency. In this thesis, the bixin extracted from annatto (Bixa orellana L.) seeds was used as sensitizer. To improve its stability and the performance of the DSSC, the use of activated kaolinite was also studied. A high efficiency DSSC requires a photo-electrode with a high surface area to effectively adsorb the dye. So the couple of TiO2/kaolinite photo-electrode was prepared for this purpose. It is considered that kaolinite can confine the incident light within the electrode and can also improve the conduction of electrons. In this system, kaolinite also has an important role to increase the photostability of bixin. Another factor affecting the performance of DSSC is the important role of the electrolyte. In these studies, cyclic organic carbonates that have a high dielectric constant and also a high boiling point (above 300oC) were evaluated as solvents in the electrolyte. These works were carried out in four stages: (1) extraction, purification and characterization of bixin, (2) preparation, characterization and activation of kaolinite, (3) study of adsorption of bixin on the surface of kaolinite and TiO2, and (4) manufacturing of bixin sensitized solar cell (BSSC). The results show that the accelerated solvent extraction using a mixture of 60% cyclohexane and 40% acetone can be an effective method of extraction for bixin. After purification by flash chromatography, bixin with a degree of purity of 99.86% was isolated. It is composed of 88.11% cisbixin and 11.75% di-cis-bixin. The activation of calcined kaolinite (metakaolinite) by ammonia is a good method to produce kaolinite with very high specific surface area and a higher Si/Al ratio. The absorption study bixin has shown that the dimethyl carbonate is a suitable solvent for bixin. It allows bixin to have a high absorption coefficient and good adsorption characteristics onto the surface of the photo-electrode. The monolayer adsorption of bixin on the surface of TiO2 or kaolinite is more favorable to obtain higher energy efficiency. The presence of activated metakaolinite in the photo-electrode TiO2 has proven to improve the performance and stability of the BSSC compared to the BSSC manufactured with the pure TiO2 photo-electrode. These performances are reproducible. The electrolyte has a synergistic effect with the activated metakaolinite for improving the electrical parameters of the BSSC. Under a light intensity of 200 W/m2, the BSSC including a photo-electrode of TiO2 modified by 5% of the activated metakaolinite and KI/I2 electrolyte system in glycerol carbonate acetate produced an energy efficiency of (0.050+ 0.006)%, which is higher than that of the BSSC comprising a pure TiO2 photoelectrode (0.027+0.012)%. The use of LiI/I2 a redox couple in the glycerol carbonate acetate produces the maximum energy efficiency of (0.086+0.014)%. Its function of energy storage and loading worked well until the third day of analysis. To date, the BSSC manufactured using the photoelectrode TiO2 modified by activated metakaolinite is 16 times more stable than the BSSC manufactured using the pure TiO2 photo-electrode.

To design an efficient solar energy conversion device, theoretical input is extremely important to provide the basic guideline for experimental scientists, to fabricate the most efficient, cheap, and stable device with less efforts. This desire can be made possible if computational scientist use a proper theoretical protocol, design an energy material, then the experimentalist will only invest weeks or months on the synthetic effort. This thesis highlights my recent efforts in this direction. Monoclinic BiVO4 is has been using as a photocatalyst due to its stability, cheap, easily synthesizable, narrow band gap and ideal VB (-6.80 eV vs vacuum) but inappropriate CB (-4.56 eV vs vacuum) edge position, responsible for its low efficiency. We have carried out a comprehensive experimental and periodic density functional theory (DFT) simulations of the pristine, Oxygen defective (Ov), Se doped monoclinic BiVO4 and heterojunction with Selenium (Se-BiVO4), to improve not only its CB edge position but photocatalytic and charge carrier properties. It is found that Ov (1% Oxygen vacancy) and mild doped BiVO4 (1 to 2% Se) are thermodynamically stable, have ideal band edges ~ -4.30 eV), band gaps (~1.96 eV), and small effective masses of electrons and holes. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption and charge transfer properties in heterojunction. Finally, it is found that Se makes a direct Z-scheme (band alignments) with BiVO4 where the photoexcited electron of BiVO4 recombine with the VB of Se, consequences electron-hole separation at Se and BiVO4, respectively, as a result, enhanced photocurrent is obtained. Theoretical study of β-TaON in the form of primitive unit cell, supercell and its N, Ta, and O terminated surfaces are carried out with the help of periodic DFT. Optical and electronic properties of all these different species are simulated, which predict TaON as the best candidate for photocatalytic water splitting contrast to their Ta2O5 and Ta3N5 counterparts. The calculated bandgap, valence band, and conduction band edge positions predict that β-TaON should be an efficient photoanodic material. The valence band is made up of N 2p orbitals with a minor contribution from O 2p, while the conduction band is made up of Ta 5d. Turning to thin films, the valence band maximum; VBM (−6.4 eV vs. vacuum) and the conduction band minimum; CBM (−3.3 eV vs. vacuum) of (010)-O terminated surface are respectively well below and above the redox potentials of water as required for photocatalysis. Charge carriers have smaller effective masses than in the (001)-N terminated film (VBM −5.8 and CBM −3.7 eV vs. vacuum). However, due to wide band gap (3.0 eV) of (010)-O terminated surface, it cannot absorb visible wavelengths. On the other hand, the (001)-N terminated TaON thin film has a smaller band gap in the visible region (2.1 eV) but the bands are not aligned to the redox potential of water. Possibly a mixed phase material would produce an efficient photoanode for solar water splitting, where one phase performs the oxidation and the other reduction. Computational study of an optically transparent, near-infrared-absorbing low energy gap conjugated polymer, donor−acceptor−donor (D-A-D) with promising attributes for photovoltaic application is reported herein. The D and A moiety on the polymeric backbone have been found to be responsible for tuning the band gap, optical gap, open circuit (Voc) and short-circuit current density (Jsc) in the polymers solar cells (PSC). Reduction in the band gap, high charge transformation, and enhanced visible light absorption in the D-A-D system is because of strong overlapping of molecular orbitals of D and A. In addition, the enhanced planarity and weak steric hindrance between adjacent units of D-A-D, resulted in red-shifting of its onset of absorption. Finally, PSC properties of the designed D-A-D was modeled in the bulk heterojunction solar cell, which gives theoretical Voc of about 1.02 eV. DFT study has been carried out to design a new All-Solid-State dye-sensitized solar cell (SDSC), by applying a donor-acceptor conjugated polymer instead of liquid electrolyte. The typical redox mediator (I1−/I3−) is replaced with a narrow band gap, hole transporting material (HTM). A unique “upstairs” like band energy diagram is created by packing N3 between HTM and TiO2. Our theoretical simulations prove that the proposed configuration will be highly efficient as the HOMO level of HTM is 1.19 eV above the HOMO of sanitizer (dye); providing an efficient pathway for charge transfer. High short-circuit current density and power conversion efficiency is promised from the strong overlapping of molecular orbitals of HTM and sensitizer. A low reorganization energy of 0.21 eV and exciton binding energy of 0.55 eV, confirm the high efficiency of HTM. Theoretical and experimental studies of a series of four porphyrin-furan dyads were designed and synthesized, having anchoring groups, either at meso-phenyl or pyrrole-β position of a zinc porphyrin based on donor–π–acceptor (D–π–A) approach. The porphyrin macrocycle acts as donor, furan hetero cycle acts as π-spacer and either cyanoacetic acid or malonic acid group acts as acceptor. Optical bandgap, natural bonding, and molecular bonding orbital (HOMO–LUMO) analysis confirm the high efficiency pyrrole-β substituted zinc porphyrins contrast to meso-phenyl dyads. DFT study of polypyrrole-TiO2 composites has been carried out to explore their optical, electronic and charge transfer properties for the development of an efficient photocatalyst. Titanium dioxide (Ti16O32) was interacted with a range of pyrrole (Py) oligomers to predict the optimum composition of nPy-TiO2 composite with suitable band structure for efficient photocatalytic properties. The study has revealed that Py-Ti16O32 composites have narrow band gap and better visible light absorption capability compared to individual constituents. A red-shifting in λmax, narrowing band gap, and strong intermolecular interaction energy (-41 to −72 kcal/mol) of nPy-Ti16O32 composites confirm the existence of strong covalent type interactions. Electron−hole transferring phenomena are simulated with natural bonding orbital analysis where Py oligomers found as donor and Ti16O32 as an acceptor in nPy-Ti16O32 composites. Sensitivity and selectivity of polypyrrole (PPy) towards NH3, CO2 and CO have been studied at DFT. PPy oligomers are used both, in the doped (PPy+) and neutral (PPy) form, for their sensing abilities to realize the best state for gas sensing. Interaction energies and amount of charges (NBO and Mulliken charge analysis) are simulated which reveal the sensing ability of PPy towards these gases. PPy, both in doped and neutral state, is more sensitive to NH3 compared to CO2 and CO. More interestingly, NH3 causes doping of PPy and de-doping of PPy+, providing evidence that PPy/PPy+ is an excellent sensor for NH3 gas. UV-vis and UV-vis-near-IR spectra of nPy, nPy+, and nPy/nPy+-X complexes demonstrate strong interaction of PPy/PPy+ with these atmospheric gases. The applications of graphene (GR) and its derivatives in the field of composite materials for solar energy conversion, energy storage, environment purification and biosensor applications have been reviewed. The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing and removal of heavy metal ions is presented. Additionally, the presences of graphene composites in the bio-sensing field have been also discussed in this review.

O objetivo do trabalho foi demonstrar que o polivinilcarbazol (PVK) dopado com Perclorato de Lítio (LiClO4) pode converter energia luminosa em energia elétrica. Esse material polimérico possui a propriedade de absorver e gerar pares de elétron-lacunas fornecendo uma corrente elétrica quando exposto à iluminação. Para essa finalidade foi construído um dispositivo (célula solar) com a seguinte estrutura: vidro / ITO / a-Si:H (p) / polímero PVK / µ-Si:H (n) / Al, tendo o PVK dopado como camada ativa. O estudo proposto, dessa maneira, teve como finalidade: pesquisar, desenvolver, fabricar e caracterizar esse dispositivo, analisando suas características elétricas e ópticas, sua eficiência de conversão (rendimento) e outros fatores relacionados ao seu desempenho e do processo de fabricação. / The objective of this article is to demonstrate that the Poly(N-vinylcarbazole) PVK dumped with lithium perchlorate (LiClO4) can transform solar energy to electrical energy. This polymer material has the property of absorbing and generate electron hole pairs, providing an electric current when exposed to enlightenment. To achieve that, a solar cell has been constructed with the follow structure: glass structure/ITO/a-Si:H (p)/polymer PVK/µ-Si:H (n)/Al, with the PVK working as active layer. This proposed article had the objective to research, develop, construct and characterize this device, analyzing its electrical and optical characteristics, efficiency and other topics related to its development and construction process.