¿Que estoy leyendo? Información útil para mejorar la presencia online

Recientemente re-abri mi blog con la intención de construir un perfil acádemico e incluir  las lecturas cientificas que realizo de forma periodica para manterme actualizado sobre el desarrollo de materiales semiconductores de película delgada. 

Redacción del blog y muestra de una anotación realizada de una tesis doctoral sobre desarrollo de kesteritas

La idea de compartir la revisión de literatura surge de la experiencia personal en manejo de información del material científicos leído. De forma personal el proceso que yo sigo es el siguiente:  

• Búsqueda de contenido
• Descargar artículo cientifico y guardar en la computadora 
• Leer con un lector de PDF o un organizador de artículos como MENDELEY
• Resaltar las secciones interesantes y hacer notas personales
• Compartir y discutir los descubrimientos con los compañeros del grupo de trabajo 
• Nota: La discusión se encuentra en función del numero de participantes del grupo de trabajo con tema afín, en caso de no contar con compañeros es indispensable discutir con el mentor o investigador principal a cargo.

Todo este proceso se lleva acabo de forma física y personal. Esto quiere decir que el archivo de notas y los artículos descargados quedan resguardados de forma física en la computadora personal o en la proporcionada por la  institución. La información corre el riesgo de desaparecer, claro esta que el conocimiento adquirido se mantendrá en cada uno de nosotros. Esto ultimo no se juzga, pero estamos aquí para hablar sobre ¿Que estoy leyendo?.

Obviamente, siguiendo la moda en curso sobre las redes sociales. Mencionar a nuestros pares académicos o dar la oportunidad de que ellos conozcan cual es la literatura que nos encontramos leyendo demuestra que estamos activos consumiendo contenido científico y  por lo cual estamos actualizados respecto al tema de interés. A mi parecer esta es una forma de construir un perfil académico. La cuestión ahora es ¿Como lo hacemos?

Paper: Identifying the Real Minority Carrier Lifetime in Nonideal Semiconductors: A Case Study of Kesterite Materials

Title: Identifying the Real Minority Carrier Lifetime in Nonideal Semiconductors: A Case Study of Kesterite Materials
Authors: Charles J. Hages,* Alex Redinger, Sergiu Levcenko, Hannes Hempel, Mark J. Koeper, Rakesh Agrawal, Dieter Greiner, Christian A. Kaufmann, and Thomas Unold*
Link: Adv. Energy Mater. 2017, 1700167 (Cited by 16)

Abstract:

Time‐resolved photoluminescence (TRPL) is a powerful characterization technique to study carrier dynamics and quantify absorber quality in semiconductors. The minority carrier lifetime, which is critically important for high‐performance solar cells, is often derived from TRPL analysis. However, here it is shown that various nonideal absorber properties can dominate the TRPL signal making reliable extraction of the minority carrier lifetime not possible. Through high‐resolution intensity‐, temperature‐, voltage‐dependent, and spectrally resolved TRPL measurements on absorbers and devices it is shown that photoluminescence (PL) decay times for kesterite materials are dominated by minority carrier detrapping. Therefore, PL decay times do not correspond to the minority carrier lifetime for these materials. The lifetimes measured here are on the order of hundreds of picoseconds in contrast to the nanosecond lifetimes suggested by the decay curves. These results are supported with additional measurements, device simulation, and comparison with recombination limited PL decays measured on Cu(In,Ga)Se2. The kesterite material system is used as a case study to demonstrate the general analysis of TRPL data in the limit of various measurement conditions and nonideal absorber properties. The data indicate that the current bottleneck for kesterite solar cells is the minority carrier lifetime.

Highlights:

• PL decay times or TRPL do not correspond to the minority carrier lifetime for CZTSe
• Processes which influence the TRPL decay are: 
• Radiative and nonradiative recombination
• Surface recombination
• Carrier drift in an electric field
• Absorber inhomogeneity
• Material degradation
• Minority carrier trapping  (capture and emission)
• For kesterites, the connection between PL time decay and the assumed minority charge lifetime is not apparent. (For CdTe technology is correlated)
• V-TRPL: In contrast to CIGSe the TRPL data of kesterites shows no dependence on voltage.  

Characterization techniques:

• Steady-state PL (photoluminescence)
• TRPL - Time-resolved photoluminescence is used to study carrier dynamics and quantify absorber quality in semiconductors: (Minority carrier lifetime and charge carrier density)
• Intensity-dependent TRPL
• Voltage-dependent TRPL
• Temperature-dependent TRPL  

Video: Analysis of techniques for measuring carrier recombination lifetime

Author:  Dr. Richard K. Ahrenkiel is a Research Professor of Metallurgical and Materials Engineering at the Colorado School of Mines in Golden, Colorado.

Abstract

Rapid, accurate and contactless measurement of the recombination lifetime is a very important activity in photovoltaics. The excess carrier lifetime (Δn(t)) is the most critical and variable parameter in the development of photovoltaic materials. Device performance can be accurately predicted from the lifetime measurement of the starting material. However, there is no single measurement that directly measures the bulk lifetime as all measurements are based on a device model.

A primary issue is that the lifetime is a function of excess carrier lifetime, and measurements must be linked to an injection level. The most common measurements are based on either photoconductive (PCD) or photoluminescence (TRPL) decay. PC decay senses the product of excess carrier concentration (Δn) and mobility (μ (Δn)). This mobility variation must be included in order to extract the true excess carrier lifetime. TRPL works best for direct band gap materials and therefore is not applicable to silicon. For polycrystalline materials, shallow traps distort the measurement and must be included in the analysis of the data. Finally, surface and interface recombination have a profound influence on most measurements and must be minimized for accurate measurement of the true bulk lifetime.

Both techniques and analysis methods will be discussed in this seminar. Typical sample measurements will be shown, including representative thin film and wafer materials that are currently popular in the photovoltaic community.

Richard Keith Ahrenkiel (2013), "Analysis of Techniques for Measuring Carrier Recombination Lifetime," https://nanohub.org/resources/19884