Nanoscale Investigation Of Potential Distribution In Operating Cu In Ga Se2 Thin Film Solar Cells

The distribution of the electrostatic potential in and between the materials in Cu(In,Ga)Se2 thin-film solar cells has a major impact on their superior performance. This thesis reported on the nanoscale imaging of the electrostatic potential on untreated cross sections of operating Cu(In,Ga)Se2 solar cells using Kelvin probe force microscopy.

As an alternative for Si-based solar cells Cu2ZnSn(S,Se)4 (CZTSSe) and Cu(In,Ga)Se2 (CIGS) thin film solar cells have recently received great attention as their efficiency has been steadily increased over the past decades. Nevertheless, the efficiency is still below the theoretically predicted upper limit, which is mainly related to inhomogeneities in the absorber composition, structural defects, and the formation of secondary phases. This thesis provides insights into efficiency-limiting properties of highly efficient Ge-doped CZTSe, CZTSSe, and CIGS thin film solar cells by accessing local compositional, structural, microstructural, and functional properties using a combinatorial approach of electron- and advanced synchrotron-based methods at the nanoscale: First, it has been demonstrated that an exceptionally homogeneous element distribution in the CZTSe absorber accompanied by the absence of harmful Cu-, Zn- or Sn-based secondary phases is achieved by introducing small amounts of Ge during the synthesis. Within the absorber, Ge is heterogeneously incorporated into the CZTSe matrix, but also forms nanoscale GeO2 secondary phases. Second, the interplay of performance-limiting nanoscale features in CZTSSe solar cells were revealed. Investigations of the local composition indicates the formation of harmful ZnS(Se) secondary phases whose presence, number, and dimension increases strongly with the reduction of Cu and the increase of Zn content. Furthermore, the local composition of the CZTSSe phase shows strong variations within the absorber, which significantly reduces the efficiency. Third, a CIGS solar cell that underwent a post-deposition treatment with RbF was investigated in a combinatorial approach, which simultaneously monitors the local composition and device functionality. This work demonstrates that Rb-enriched grain boundaries have a negligible influence on the collection efficiency, indicating the passivation of detrimental defects.

This book offers a bird’s-eye view of the recent development trends in photovoltaics – a big business field that is rapidly growing and well on its way to maturity. The book describes current efforts to develop highly efficient, low-cost photovoltaic devices based on crystalline silicon, III–V compounds, copper indium gallium selenide (CIGS) and perovskite photovoltaic cells along with innovative, cost-competitive glass/ flexible tubular glass concentrator modules and systems, highlighting recent attempts to develop highly efficient, low-cost, flexible photovoltaic cells based on CIGS and perovskite thin films. This second edition presents, for the first time, the possible applications of perovskite modules together with Augsburger Tubular photovoltaics.

Thin-film solar cells are either emerging or about to emerge from the research laboratory to become commercially available devices finding practical various applications. Currently no textbook outlining the basic theoretical background, methods of fabrication and applications currently exist. Thus, this book aims to present for the first time an in-depth overview of this topic covering a broad range of thin-film solar cell technologies including both organic and inorganic materials, presented in a systematic fashion, by the scientific leaders in the respective domains. It covers a broad range of related topics, from physical principles to design, fabrication, characterization, and applications of novel photovoltaic devices.

Thin-film solar cells potentially offer a suitable technology for solving the energy production problem with an environmentally friendly method. This book presents a range of scientific and technological aspects on thin film semiconductors, deposition technologies, basic properties and device physics of high-efficiency thin film solar cells.