High Efficiency Cascade Solar Cells
This report summarizes the main work performed by New Mexico State University and University of Houston on a DOE sponsored project High Efficiency Cascade Solar Cells. The main tasks of this project include materials synthesis, characterization, theoretical calculations, organic solar cell device fabrication and test. The objective of this project is to develop organic nano-electronic-based photovoltaics. Carbon nanotubes and organic conjugated polymers were used to synthesize nanocomposites as the new active semiconductor materials that were used for fabricating two device architectures: thin film coating and cascade solar cell fiber. Chemical vapor deposition technique was employed to synthesized a variety of carbon nanotubes (single-walled CNT, doubled-walled CNT, multi-walled CNT, N-doped SWCNT, DWCNT and MWCNT, and B-doped SWCNT, DWCNT and MWCNT) and a few novel carbon structures (CNT-based nanolance, nanocross and supported graphene film) that have potential applications in organic solar cells. Purification procedures were developed for removing amorphous carbons from carbon nanotubes, and a controlled oxidation method was established for partial truncation of fullerene molecules. Carbon nanotubes (DWCNT and DWCNT) were functionalized with fullerenes and dyes covalently and used to form nanocomposites with conjugated polymers. Biologically synthesized Tellurium nanotubes were used to form composite with the conjugated polymers as well, which generated the highest reported optical limiting values from composites. Several materials characterization technique including SEM/TEM, Raman, AFM, UV-vis, adsorption and EDS were employed to characterize the physical and chemical properties of the carbon nanotubes, the functionalized carbon nanotubes and the nanocomposites synthesized in this project. These techniques allowed us to have a spectroscopic and morphological control of the composite formation and to understand the materials assembled. A parallel 136-CPU Beowulf computer cluster was launched intended to be used as the main computational tool for the theoretical part of this project. The mechanism of surface carboxylation of pristine and defective carbon nanotubes were studied using the computation method. Theoretical studies of boron- and nitrogen-doped carbon nanotubes functionalized with chemical groups, and CdSe/ZnSe, ZnSe/CdSe, CdTe/ZnTe, and ZnTe/CdTe core-shell semiconductor nanoparticles embedded in electroactive polymers were also carried out. We have successfully fabricated singular champion cells with Voc of 0.6 V and Jsc of 15 mA, and developed the pixel cells and with a working areas over 25mm2, 2.5 % efficiency for a multicell arrangement, and a stability of 40% of their initial efficiency after 11,000 minutes. We have also demonstrated the feasibility of using a gold film as an alternative semi-transparent electrode for organic solar cell applications. An efficiency of 1.9 % (JSC of 7.01 mA/cm2, VOC of 0.55 V, FF of 0.49) can be reached by using the gold film as an anode instead of ITO. Two new vertical organic solar cell architectures: stack cells and wrap cells, suitable as an alternative to planar devices were developed as well. We have proved the feasibility of replacing ITO with more traditional metals without hindering performance, and developed natural encapsulation techniques during device fabrication. Optical modeling of the stack cells was also performed to enhance our understanding of this device configuration.
- Research Organization:
- New Mexico State Univ., Las Cruces, NM (United States)
- Sponsoring Organization:
- EERE: Solar Energy Technologies Program
- DOE Contract Number:
- FG36-08GO88008
- OSTI ID:
- 1015879
- Report Number(s):
- DOE/GO/88008-1
- Country of Publication:
- United States
- Language:
- English
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