## Solid state, Semiconductors, Electrochemistry, and Nanowires for Solar Cells

Submitted by Jeremiah Duncan, Plymouth State UniversityThis learning object has not yet been tested.

This learning object has not yet been tested.

This Literature Discussion learning object (LO) is based on the paper “Template Electrodeposition of Single-Phase *p*- and *n*-Type Copper Indium Diselenide (CuInSe_{2}) Nanowire Arrays,” Emil A. Hernández-Pagán, Wei Wang, and Thomas E. Mallouk, *ACS Nano*, **2011**, 5 (4), pp 3237–3241. DOI: 10.1021/nn200373k

This paper is about the synthesis and characterization of CuInSe_{2} nanowires using templates and electrodeposition. It is found that varying the potential of the electrodeposition influences the relative stoichiometry of the Cu and In atoms. Lower (more negative) potentials result in In-rich, *n*-type nanowires and higher potentials result in Cu-rich, *p*-type nanowires. These materials may find utility in solar cells, and nanowire geometry is predicted to result in more efficient solar-to-electrical conversion.

This paper covers topics in the following four categories: 1) electrochemistry, 2) nanomaterials, 3) semiconductors, and 4) solid state structures (including diffraction). Because these topics may be covered in different orders by different instructors, this LO has been designed to be modular to allow this Literature Discussion to occur at various points in the curriculum. Learning goals and relevant guiding questions have thus been grouped under each of these categories to help focus discussions. This LO may serve as a good review at the end of a course that covers all of these categories, though there is more here than can likely be covered in a single class. Therefore, it is assumed that, when implemented, instructors will choose to use individual learning goals/guiding questions or entire categories. Please implement and post any handouts or modifications that you create!

The creators of this learning object gratefully acknowlege Tom Mallouk (The Pennsylvania State University) for his contributions and insights to our group's discussions.

In reading this paper and participating in the literature discussion, students will:

__Electrochemistry __

- Calculate concentrations of electrolyte components based on stoichiometry.
- Rank elements in order of ease of reduction.
- Apply knowledge from the electrochemical series to understanding the synthesis of CuInSe
_{2}. - Relate understanding of standard reduction potentials to topics in the current literature.

__Nanomaterials __

- Use TEM images to describe the dimensions of the synthesized nanowires.
- Describe a unique property of nanowires relative to the bulk material that may improve their utility in solar cells.
- Apply the relationship between grain size and peak broadening in XRD patterns using the Scherrer equation.

__Semiconductors__

- Define
*p*-type and*n*-type semiconductors. - Understand band diagrams for
*p*-type and*n*-type semiconductors and for*p-n*junctions and use these to explain the unique properties of a*p-n*junction. - Apply basic electron count process to predict doping type in extrinsic semiconductors.
- Distinguish the properties of direct and indirect band gap semiconductors.
- Describe quantitatively and qualitatively the relationships between semiconductor band gap energy and the absorption and reflection of visible light.
- Describe the four-probe method and distinguish between resistance and resistivity.

__Solid state__

- Understand ionic solid unit cells and how similar unit cells relate to each other:
- describe the zinc blende structure.
- describe the relationship of the zinc blende structure to the chalcopyrite structure.
- determine the coordination environments of atoms in the unit cell of chalcopyrite, specifically CuInSe
_{2}. - understand the concept of solid solutions and how different ions can occupy the same lattice sites in an extended ionic solid.

- Define the nomenclature of Miller indices for lattice planes. Relate a particular set of Miller planes for a material to the unit cell and observed peaks in X-ray powder diffraction patterns.
- Calculate and interpret mole ratios from elemental analysis data.