Hysteresis and Capacitive Features of Perovskite Solar Cells
- Autores: Osbel Almora Rodríguez
- Directores de la Tesis: Germà García Belmonte (dir. tes.), Christoph Brabec (codir. tes.)
- Lectura: En la Universitat Jaume I ( España ) en 2020
- Idioma: inglés
- Número de páginas: 133
- Tribunal Calificador de la Tesis: Robert Schober (presid.), Francisco Fabregat Santiago (secret.), Wolfgang Heiss (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencias por la Universidad Jaume I de Castellón
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
- español
En el presente trabajo se estudian por varios métodos las distorsiones anómalas en la característica de corriente-voltaje de las celdas solares de perovskita (PSC), típicamente llamada histéresis de J-V. Esto incluye experimentos dinámicos de J-V en modo de corriente continua (DC) y análisis de espectroscopía de impedancia (IS) en oscuridad y bajo iluminación. Las curvas J-V en oscuridad de las PSCs exhiben corrientes capacitivas, relacionadas con un exceso de capacitancia de baja frecuencia en los espectros de IS. Estas dos características están correlacionadas con la respuesta de iones móviles en regiones espaciales de carga hacia las interfaces. Los grandes valores de capacitancia bajo iluminación a frecuencias por debajo de las unidades de Hz se explicaron en términos de regiones de cargas espaciales de iones móviles y capacitancias químicas, suponiendo una proporcionalidad entre el número de iones móviles ionizados/activados y la concentración de portadores de carga y flujo de fotones.
- English
In the present work, anomalous distortions occurring in the current-voltage characteristic of perovskite solar cells (PSCs), usually called J-V curve hysteresis, are studied by several methods. This includes dynamic direct current (DC) mode J-V experiments and impedance spectroscopy (IS) analyses in dark and under illumination. Initially, the CH3NH3PbI3 absorber material is characterized by alternating current (AC) and transient techniques showing ionic-related features. Subsequently, dark J-V curves of PSCs measured under different conditions are shown to exhibit capacitive hysteretic currents. This is related with low frequency excess capacitance in the dark IS spectra. These two features are correlated with the response of mobile ions in space charge regions close to the interfaces. The ion-related low frequency capacitance is shown to hinder the evaluation of deep trap and shallow doping concentrations from IS analyses as a function of temperature and DC bias, i.e. TAS and Mott-Schottky analysis, respectively. The light J-V curve hysteresis was checked at faster scan rates after pre-bias in different device structures. The results were simulated by drift diffusion methods, suggesting that the formation of ionic dipoles can create large hysteresis. The light IS analyses at open-circuit allowed to identify different recombination mechanisms via ideality factor parametrization and revealed different exponential trends for the low-frequency capacitance. The low frequency capacitance was also studied at short-circuit under light and forward bias in the dark. The large values of capacitance in the sub-Hz regime were explained in terms of mobile ions space charges and chemical capacitances assuming a proportionality between the number of ionized/activated mobile ions and the concentration of charge carriers and photon fluence. Finally, a new method of characterization of photo-sensitive devices was introduced, named light intensity modulated impedance spectroscopy (LIMIS). This is based on the evaluation of photo-impedance from both, the individual photovoltage and photocurrent signals, under small AC light perturbation at DC open circuit. The impedance difference between IS and LIMIS informs on recombination velocity in traditional photovoltaics. Preliminary measurements of LIMIS in PSCs reveal significant impedance differences as light intensity increases and provide improved measurements of charge carrier lifetimes.
- español
