Graduate Student, Materials Chemistry
Department of Chemistry
University of Wisconsin-Madison

mcaban@chem.wisc.edu

Biographical Sketch
B.S. University of Puerto Rico-Rio Piedras, Chemistry, 2004-2009
PhD University of Wisconsin-Madison, 2009-Present

Research

My research involves the investigation of earth-abundant solar materials towards enabling inexpensive yet high performance photovoltaic devices (Ex. liquid-junction, solid-state, and hybrid devices.). One earth-abundant solar material that we are intensively investigating is iron pyrite (cubic FeS₂). As the most abundant sulfide mineral in the earth’s crust, iron pyrite practically has unlimited material supply to satisfy our energy demand. It is a very interesting semiconducting material for solar applications due to its band gap (0.95 eV), high absorption coefficient (6 × 10⁵ cm^-1) and other superior semiconducting properties (such as high carrier mobility and lifetime) in single-crystalline iron pyrite. Despite its attractive properties, high solar energy conversion efficiency has never been achieved with iron pyrite. Evidence suggests iron pyrite is a complex semiconductor that is riddled with various intrinsic bulk and surface defects, and it demands further investigation. Towards understanding such defects in iron pyrite, in my initial work, we achieved the synthesis of phase pure and single-crystalline iron pyrite nanostructures (Figure 1b-g),^6,7 with the purpose of utilizing them as suitable study platforms. In particular, we demonstrated that high-quality nanoscale iron pyrite building blocks, such as single-crystalline NWs and nanoplates (Figure 1b-g), are an attractive platform for the fundamental investigation of intrinsic semiconductor properties, including surface and interfacial properties.^2,6

In order to understand the origin of the low photovoltage and poor photovoltaic performance of iron pyrite materials, I conducted a comprehensive investigation on the properties of {100}-faceted n-type single crystals.¹ We utilized electrical transport, optical spectroscopy, surface photovoltage, photoelectrochemical measurements in aqueous and acetonitrile electrolytes, UV and X-ray photoelectron spectroscopy, and Kelvin force microscopy to characterize the bulk and surface defect states and their influence onthe semiconducting properties and solar conversion efficiency of iron pyrite single crystals. These insights were used todevelop a circuit model analysis for the electrochemical impedance spectroscopy that allowed a complete characterization of the bulk and surface defect states and the construction of a detailed band energy diagram for iron pyrite crystals (Figure 1h). A holistic evaluation revealed that the high-density of intrinsic surface states responsible for the strong Fermi level pinning cannot satisfactorily explain the low photovoltage; instead the ionization of high-density bulk deep donor states, likely resulting from bulk sulfur vacancies, creates a non-constant charge distribution and a very narrow surface space charge region that limits the total barrier height, and satisfactorily explains the limited photovoltage and poor photoconversion efficiency of iron pyrite single crystals.

Figure 1. (a) Photograph of mineral pyrite; (b) SEM images of phase-pure pyrite nanorods, microrods, nanobelts and nanoplates, and a lattice-resolved high-resolution transmission electron micrograph (HRTEM) showing their single-crystalline structure;^3,4 (c) Temperature-dependent electrical transport measurements for a single pyrite nanorod that illustrates the defect-mediated hopping conduction transport.³

Publications

1) Li, L.; Cabán-Acevedo, M.; Girard, S. N.; Jin, S. High-Purity Iron Pyrite (FeS₂) Nanowires as High-Capacity Nanostructured Cathodes for Lithium-Ion Batteries. Small. 2013, Submitted. (Co-First Author)

2) Faber, M. S.; Park, K.; Cabán-Acevedo, M.; Santra, P. K.; Jin, S. Earth-Abundant Cobalt Pyrite (CoS₂) Thin Film on Glass as a Robust, High-Performance Counter Electrode for Quantum Dot-Sensitized Solar Cells. J. Phys. Chem. Lett. 2013, 4, 1843-1849.

3) Cabán-Acevedo, M.; Liang, D.; Chew, K. S.; DeGrave, J. P.; Kaiser, N. S.; Jin, S. Synthesis, Characterization, and Variable Range Hopping Transport of Pyrite (FeS₂) Nanorods, Nanobelts, and Nanoplates. ACS Nano 2013, 7, 1731-1739.

4) Cabán-Acevedo, M.; Faber, M. S., Tan, Y., Hamers, R. J., Jin, S.Synthesis and Properties of Semiconducting Iron Pyrite (FeS₂) Nanowires. Nano Lett. 2012, 12, 1977.

5) Feliciano-Ramos, I.; Cabán-Acevedo, M.; Scibioh, A.; Cabrera, C. R. Self-assembled monolayers of l-cysteine on palladium electrodes. J Electroanal Chem.2010, 650. 98-104.

6) Cabán-Acevedo, M.; Liang, D.; Chew, K. S.; DeGrave, J. P.; Kaiser, N. S.; Jin, S. Synthesis, Characterization, and Variable Range Hopping Transport of Pyrite (FeS₂) Nanorods, Nanobelts, and Nanoplates. ACS Nano 2013, 7, 1731-1739.

7) Cabán-Acevedo, M.; Faber, M. S., Tan, Y., Hamers, R. J., Jin, S.Synthesis and Properties of Semiconducting Iron Pyrite (FeS₂) Nanowires. Nano Lett. 2012, 12, 1977.

8) Feliciano-Ramos, I.; Cabán-Acevedo, M.;Scibioh, A.; Cabrera, C. R. Self-assembled Monolayers of L-Cysteine on Palladium Electrodes. J. Electroanal. Chem.2010, 650. 98-104.

Conference Presentations

1) Cabán-Acevedo, M.; Faber, M. S.; Tan, Y.; Hamers, R. J.; Jin, S.Investigation of Surface Inversion and Improvement of Pyrite Single Crystals and Nanostructures for Solar Energy Conversion Application.Material Research Society (MRS) Spring 2013 Meeting. Poster.

2) Cabán-Acevedo, M.; Dong, L.; Jin, S.Investigation and Improvement of Nanostructure Pyrite for Solar Energy Conversion Application. International Conference on the Conversion and Storage of Solar Energy (IPS-19) 2012. Poster.

3) Cabán-Acevedo, M.; Liang, D.; Kwangsuk, P.; Matthew, F.S.; Kaiser, N.; Samad, L.; Jin, S. Enabling Earth-Abundant Pyrite (FeS₂) Semiconductor Nanostructure for High Performance Photovoltaic Devices. SunShot Summit 2012. Poster.

4) Cabán-Acevedo, M.; Faber, M. S., Tan, Y., Hamers, R. J., Jin, S.Synthesis of Pyrite Nanowires for High Performance and Inexpensive Photovoltaic Devices. Material Research Society (MRS) Fall 2011 Meeting. Poster.

5) Cabán, M. A.;Feliciano, I.; Cabrera, C. R. Study of L-Cysteine Self Assembled Monolayer on Palladium Surface. Electrochemical Society ECS Meeting Abstracts 2007, 701. 52-52. Poster

6) Cabán, M. A.;Feliciano, I.; Cabrera, C. R. Study of L-Cysteine Self Assembled Monolayer on Palladium Surface. Electrochemical Society ECS Meeting Abstracts 2007, 701. 52-52. Poster.