This work reports results of a study carried out to optimize the preparation conditions of Cu2ZnSnS4 (CZTS) thin films grown by sequential deposition of Cu2SnS3 (CTS) and ZnS layers, where the Cu2SnS3 compound was grown using a novel procedure consisting of simultaneous precipitation of Cu2S and SnS2 performed by diffusion membrane assisted chemical bath deposition (CBD) technique. The precipitation across the diffusion membranes allows achieving moderate control of release of metal ions into the work solution favoring the heterogeneous growth mainly through an ion-ion mechanism. Through a parameters study, conditions were found to grow Cu2SnS3 thin films which were used as precursors for the formation of Cu2ZnSnS4 films. The formation of CZTS thin films grown in the Cu2ZnSnS4 phase was verified through measurements of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Solar cells with efficiencies of 4.9% were obtained using CZTS films prepared by membrane assisted CBD technique as absorber layer.

Resumen En este trabajo se usan las celdas solares para enseñar a los estudiantes de educación media los conceptos básicos de electricidad y la importancia del uso de fuentes de energía renovable y no contaminante para generar electricidad. Para lograr estos objetivos se diseñó y desarrollo un programa de actividades pedagógicas en el cual se usaron diferentes metodologías y se llevaron a cabo varias actividades dentro del proceso de enseñanza-aprendizaje. Las actividades desarrolladas permitieron enseñar a las nuevas generaciones las ventajas de usar la energía solar para obtener energía eléctrica, con respecto al uso de fuentes de energía no renovables que principalmente se usan en la actualidad. Mediante el funcionamiento de un dispositivo de alta tecnología como la celda solar, se enseñaron los conceptos de corriente eléctrica, voltaje, resistencia y potencia eléctrica. La enseñanza de los conceptos de electricidad de esta forma novedosa constituye un ejemplo de innovación en el proceso de enseñanza-aprendizaje en el nivel de educación secundaria, que involucra el fomento del uso de energías provenientes de fuentes renovables en la enseñanza tradicional. El aprendizaje y la motivación de los estudiantes se evidenciaron en el desarrollo de proyectos escolares en los cuales utilizaron las celdas solares.

Abstract In this work, solar cells are used to teach middle school students the basic concepts of electricity and the importance of using renewable and clean energy sources to generate electricity. To achieve these objectives, a program of pedagogical activities was designed and developed in which different methodologies were used and several activities were carried out within the teaching-learning process. The activities taught the new generations the advantages of using solar energy to obtain electricity, over the use of non-renewable energy sources that are mainly used today. Through the operation of a high technology device such as the solar cell, concepts of electric current, voltage, resistance and electrical power were taught. Teaching of electricity concepts in this novel way is an example of innovation in the teaching-learning process at the level of secondary education, which involves the promotion of the use of energy from renewable sources in traditional teaching. Learning and motivation of students were evidenced in the development of school projects in which they used the solar cells.

Resumen Este trabajo describe un procedimiento para crecer in situ películas delgadas de n+-ZnO e i-ZnO altamente transparentes, depositadas secuencialmente por evaporación reactiva asistido por plasma sin usar dopaje extrínseco. Se logró una buena reproducibilidad del espesor y de las propiedades opto-eléctricas de las películas a través de un control electrónico novedoso desarrollado usando el concepto de instrumentación virtual. Para lo cual se implementó un instrumento virtual (VI) que controlaba el proceso usando PID (proporcional integral differential) y PWM (pulse width modulation) como algoritmos de control. Optimizando el diseño del reactor y los parámetros de deposición se obtuvieron con este método películas n+-ZnO e i-ZnO con resistividades alrededor de 6 x 10-4 Ωcm y 10(4) Ωcm respectivamente y transmitancias mayores al 85% (en la región visible). A partir de medidas de energía Urbach encontramos que las películas n+-ZnO depositadas controlando apropiadamente la cantidad de zinc que llega al reactor tienen una cantidad baja de defectos estructurales. También se reportan resultados relacionados con propiedades de transporte eléctrico de las películas de ZnO, obtenidas de medidas de conductividad y movilidad dependientes de la temperatura.

Abstract This work describes a procedure to grow in situ highly transparent n+-ZnO and i-ZnO thin films sequentially deposited by plasma assisted reactive evaporation without using extrinsic doping. Good reproducibility of the thickness and opto-electrical properties of the films was achieved through a novel electronic control developed using the virtual instrumentation concept. For that, a virtual instrument (VI) was implemented to control the process using PID (proportional integral differential) and PWM (pulse width modulation) as control algorithms. By optimizing the design of the reactor and deposition parameters, n+-ZnO and i-ZnO films with resistivities around 6 x 10-4 Ωcm and 10(4) Ωcm respectively and transmittances greater than 85 % (in the visible region) were obtained with this method. From Urbach energy measures we have found that n+-ZnO films deposited controlling the quantity of zinc that arrives to the reactor appropriately, have a low density of structural defects. Results regarding electrical transport properties of the ZnO films, obtained from temperature dependent measurements of both conductivity and mobility, are also reported.