Advanced search

Knowledge area

5 results, page 1 of 1

Study, fabrication and characterization of solar cells based on a-Si:H films deposited by plasma on plastic substrates.

Carlos Ospina (2018)

In this work, plastic substrates PEN, Kapton Polyimide and Teflon were characterized by means of the atomic force microscopy (AFM) technique. Parameters such as maximum height of peaks and width of defects were analyzed. Regions free of defects of these surfaces were also analyzed and the most relevant statistical parameters were determined, such as the RMS roughness, the average height, skewness and kurtosis. In addition to the morphological characterization, spectral measurements were made on the plastic substrates. It was observed that the Teflon substrate has greater optical transmission in the UV spectral region compared to PEN, and exhibits greater transmission in the visible spectrum compared with PEN and Kapton.

p-i-n structures were fabricated on plastic and glass substrates, and the evolution of the morphology in the different layers that make up the p-i-n structure was investigated. The study showed that the morphological characteristics of the surfaces depend on the material used as a substrate, as well as the type of the deposited layers. In addition, treatments with argon (Ar) plasma were studied to improve the adhesion of polymers and AZO films on plastic substrates. The optimal conditions that we found were the following: Power of 30 W, pressure equal to 0.3 Torr and time of 6 minutes. The treatment is the same if done at 110° C or at room temperature.

Planarization study of surface defects was carried out on flexible substrates. The study was characterized by AFM and transmittance. Fabrication and characterization of completely inorganic flexible solar cells and some hybrids were carried out. The performance of the solar cells was evaluated through J-V performance curves under AM1.5 illumination.

En este trabajo se caracterizaron superficies de sustratos plásticos PEN, Kapton Poliimida y Teflón por medio de la técnica de microscopía de fuerza atómica (AFM). Parámetros como altura máxima de picos y ancho de defectos se analizaron. Regiones libres de defectos de estas superficies también fueron analizadas y se determinaron los parámetros estadísticos más relevantes como son la rugosidad RMS, la altura promedio, “skewness” y curtosis. Además de la caracterización morfológica, mediciones espectrales fueron realizadas sobre los sustratos plásticos. Se observó que el sustrato Teflón posee mayor transmisión óptica en la región espectral UV en comparación con PEN, y exhibe mayor transmisión en el espectro visible comparado con PEN y Kapton.

Se fabricaron estructuras p-i-n sobre sustratos de plástico y vidrio, y se investigó la evolución de la morfología en las diferentes capas que conforman la estructura p-i-n. El estudio mostró que las características morfológicas de las superficies dependen del material usado como sustrato, así como del tipo de las capas depositadas. Además, se estudiaron tratamientos con plasma de argón (Ar) para mejorar la adhesión de polímeros y películas de AZO sobre sustratos plásticos. Las condiciones óptimas que encontramos fueron las siguientes: Potencia de 30 W, presión igual a 0.3 Torr y tiempo de 6 minutos. El tratamiento sirve igual si se hace a 110°C o a temperatura ambiente.

Estudio de planarización de defectos superficiales fue llevado a cabo sobre sustratos flexibles. El estudio se caracterizó por AFM y transmitancia. Se realizó fabricación y caracterización de celdas solares flexibles completamente inorgánicas y algunas híbridas. El rendimiento de las celdas solares fue evaluado a través de curvas de rendimiento J-V bajo iluminación AM1.5.

Doctoral thesis


Efficient ITO–Si solar cells and power modules fabricated with a low temperature technology: Results and perspectives


ITO–SiOx–nSi semiconductor–insulator–semiconductor (SIS) structures have been produced with a simple spraying technique. It is shown that the structures obtained in such a way may be considered as an induced p–n diode, in which the polycrystalline tin–doped indium oxide (ITO) layer spray deposited on the preliminary treated silicon surface leads to an inversion p-layer at the interface. Solar cells with an active area of 1–4 cm2 have been fabricated based on ITO–SiOx–nSi structures and studied. Under AM0 illumination conditions, the efficiency is nearly 11%, whereas it exceeds 12% for AM1.5 illumination conditions. The theoretical analysis provided in this work shows a good agreement with experimental results and allows for predicting the efficiency of the cells depending on the silicon electro-physical properties.


Silicon Solar cells Photovoltaics Indium tin oxide and other transparent conductors CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ELECTRÓNICA

Estudio de las características de una celda fotovoltaica para el uso eficiente de la energía solar

Solar cell characteristics study for solar energy efficient use


Las celdas solares son interesantes por generar electricidad con energía solar. Sin embargo, esta tecnología está limitada, y se requiere investigación continua de materiales y sus características ópticas para su uso eficiente. En este trabajo se estudia una celda fotovoltaica como un diodo ideal en paralelo con un generador de corriente ISC. La corriente de corto circuito queda en función del número de pares electrón-hueco generados por la absorción de la luz solar. El estudio parte de una plataforma teórica de donde se resalta la importancia de dos parámetros ópticos: la irradiancia y las características espectrales de la luz, donde las pro-piedades ópticas de los materiales de las celdas solares son importantes. Las ecuaciones básicas se utilizan para determinar las características eléctricas de salida de dichas celdas, y se realizan mediciones para corroborar el comportamiento y determinar el uso eficiente de la energía solar

Solar cells are interesting devices due to the generation of electricity via solar energy. However, this technology is limited and requires further investigation on materials optical characteristics for their efficient use. In this work a photovoltaic cell is studied as an ideal diode in parallel with a current generator, ISC. The short circuit current is in function of the electron-hole pair generated by the absorption of solar light. The study starts from theory where the importance of two optical parameters as irradiance and spectral characteristics of light, where the optical properties of solar cells materials are important. Basic equations are used to determine the electrical output of such cells and measurements to check its behavior and determine its efficient use of solar energy


INGENIERÍA Y TECNOLOGÍA Fotovoltaico Celdas solares Óptica Photovoltaics Solar cells Optics


Olivia Amargós Reyes (2019)

"In the present thesis, external quantum efficiency (EQE or IPCE) technique was implemented. This home-made set up was used as a complementary characterization to better understand solar cell performance and to find optimal fabrication conditions. Organic photovoltaic solar cells (OPVs) were fabricated using commercial electron-donor polymers PTB7, PTB7-Th and PBDB-T, and electron acceptors PC71BM, ITIC and FeS2, and by means of scanning tunneling microscopy (STM), donor film molecular ordering was analyzed. These measurements indicate that PTB7-Th film chains are somewhat thicker and less spaced than those in PTB7 based OPVs, which could possibly provide better electrical charge transport. Besides, PBDB-T, with a shorter distance between polymer backbone chains, could facilitate a more efficient intramolecular charge separation, and thus improve charge transfer from the active layer to the OPV electrodes. For PTB7 based OPVs, non-toxic iron sulfide (FeS2) nanocrystals (NCs) were added to the active layer at different weight ratios as a second electron-acceptor, achieving an increase in power conversion efficiency (PCE) of 21%. For PTB7-Th based OPVs (best achieved PCE was 7.65%), optical-electrical analyses were carried out using EQE and internal quantum efficiency (IQE), applying active layer thickness variation (from 40 to 165 nm) by means of the transfer matrix method (TMM). Our results show a significant reduction of IQE (when increasing the active layer thickness above 120 nm), and consequently, also of EQE and PCE, mainly due to the reduction in charge carrier collection probability. A comparison between the experimental measurements and theoretical simulations was discussed in order to have better understanding of the OPVs performance. Finally, PBDB-T:ITIC based OPVs were tested with different hole transport layers (HTLs): PEDOT:PSS, fluorinated reduced graphene oxide (F-rGO)/PEDOT:PSS and just F-rGO. With F-rGO/PEDOT:PSS and PEDOT:PSS as HTLs, average PCEs of 8.3% and 8.7% were achieved, respectively (the highest efficiency reached with PEDOT:PSS was 8.9%), and with F-rGO, efficiency decayed to 5.4%. Device stability maintained a similar trend with the use of either F-rGO/PEDOT:PSS or PEDOT:PSS; however, for the F-rGO case, stability showed a faster decay."

Doctoral thesis

Organic solar cells EQE STM Polymers Solar photovoltaics Renewable energy CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA LUZ LUZ

Estudio teórico-experimental sobre propiedades estructurales, ferroeléctricas y ópticas del BiFeO3 mediante impurificaciones con metales de transición

Theoretical-experimental study on structural, ferroelectric and optical properties of BiFeO3 through impurities with transition metals


Con la entrada de los materiales no centrosimétricos al campo de los fotovoltaicos, los ferroeléctricos se han considerado como una clase especial de materiales capaces de convertir la radiación electromagnética proveniente del sol en energía eléctrica. A diferencia de lo que sucede en las tecnologías basadas en semiconductores, donde se requiere una unión p-n para producir el campo eléctrico para separar las cargas fotogeneradas, en un material no centrosimétrico y particularmente un ferroeléctrico, no es necesaria y su polarización espontánea provee el campo para la separación. Si la intención es utilizar estos materiales para aprovechar la energía solar, tal ventaja solo se ve afectada por su ancho de banda prohibida (gap), típicamente mayor a los 3 eV que caracterizan a un ferroeléctrico, ya que el espectro solar está centrado en 1.4 eV, aproximadamente. Entre la inmensa cantidad de materiales ferroeléctricos existentes, el BiFeO3 se destaca por presentar una brecha de energía de aproximadamente 2.7 eV; esta característica lo convierte en un candidato prometedor para realizar ajustes que reduzcan el gap mediante la ingeniería del ordenamiento catiónico, es decir mediante substituciones selectivas, ya sea del catión A o catión B de la estructura perovskita. A lo largo de este trabajo, apoyado con resultados experimentales y teóricos basados en la teoría del funcional de la densidad (DFT por sus siglas en inglés), se desarrolla la ingeniería de ordenamiento catiónico para la cual se ha substituido el sitio A de la estructura ABX3 del BiFeO3 con el 10 % de La y, de manera independiente, se realiza la substitución del sitio B de la misma estructura con 10 % de Cr, Ni y Co. Teóricamente se determinaron las propiedades ferroeléctricas, ópticas y electrónicas de cada compuesto, describiendo con ellas la influencia de la impurificación sobre las propiedades del BFO. Experimentalmente se diseñaron películas mono capa y multicapa, cuyos resultados apoyan la posibilidad de reducir el gap vía simples impurificaciones. Para su caracterización, se midieron ciclos de histéresis, propiedades ópticas y curvas J-V que describen el comportamiento ferro-fotovoltaico y brindan además la posibilidad de implementar a los sistemas como dispositivos sensores al espectro UV.

With the entrance of non-centrosymmetric materials into the field of photovoltaics, ferroelectrics have been considered as a particular class of materials capable of converting electromagnetic radiation from the sun into electrical energy. Unlike what happens in semiconductor-based technologies, where a p-n junction is required to produce the electric field to separate the photogenerated charges, in a non-centrosymmetric material and particularly a ferroelectric, it is not necessary and its spontaneous polarization provides the field for separation. If the intention is to use these materials to take advantage of solar energy, this advantage is only affected by its bandgap (gap), typically higher than the 3 eV that characterizes a ferroelectric, since the solar spectrum is centered at 1.4 eV, approximately. Among the immense amount of existing ferroelectric materials, BiFeO3 stands out for presenting a gap of approximately 2.7 eV; this characteristic makes it a promising candidate for adjustments to reduce the gap by means of the engineering of cationic ordering, that is by means of selective substitutions, either of cation A or cation B of the perovskite structure. Throughout this work, supported by experimental and theoretical results based on the density functional theory (DFT), cationic ordering engineering is developed for which site A of the structure ABX3 of BiFeO3 is substituted with 10% of La and, independently, site B of the same structure is substituted with 10% of Cr, Ni and Co. The ferroelectric, optical and electronic properties of each compound were theoretically determined, describing with them the influence of doping on the properties of BFO. Experimentally, monolayer and multilayer films were designed, whose results support the possibility of reducing the gap via simple ion substitution. For its characterization, hysteresis cycles, optical properties and J-V curves that describe the ferro-photovoltaic behavior and provide the option of implementing the systems as UV sensor devices were measured.

Doctoral thesis