Chemical disorder in semiconductors is important to characterize reliably because it affects materials performance, for instance by introducing potential fluctuations and recombination sites. It also ...represents a means to control material properties, to far exceed the limits of equilibrium thermodynamics. We present a study of highly disordered Cu–Zn–Sn–S (d-CZTS) films along the Cu2SnS3–Cu2ZnSnS4–ZnS binary line, deposited by physical vapor deposition. Deposition at low temperature kinetically stabilizes compositions that are well outside of the narrow, equilibrium solid solution of kesterite (Cu2ZnSnS4). Here we study d-CZTS and its thermal treatment using complementary characterization techniques: X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). We find that cations in d-CZTS are highly disordered while the sulfur anions remain in a well-defined, cubic close-packed lattice. On the atomic scale, composition fluctuations are accommodated preferentially by stacking faults. Kinetically-stabilized cation disorder can produce nonequilibrium semiconductor alloys with a wide range of band gap, electronic conductivity, and thermal conductivity. d-CZTS therefore represents a processing route to optimizing materials for optoelectronic device elements such as light absorbers, window layers, and thermal barriers.
Thin films of nitrogen-doped cuprous oxide (Cu sub(2)O:N) have been deposited by means of direct-current and radio-frequency sputtering using a metallic copper target and a mixture of argon, oxygen, ...and nitrogen for generating the plasma. The doping with nitrogen appears to significantly increase the electrical conductivity of the films. All samples exhibit a temperature-activated transport behavior. It is shown that the activation energy decreases proportionally to the reciprocal distance between nitrogen atoms, which indicates that a constant fraction of nitrogen is most likely substitutionally incorporated on oxygen site in the Cu sub(2)O lattice and acts as an acceptor. Nevertheless, Raman measurements suggest that molecular nitrogen can also be found in the samples, bound at different sites inside the bulk and at the surface.
Light management in the Si bottom cell of a GaAs/Si tandem system is crucial due to the bandgap mismatch of the two materials, which results in a low current of the bottom cell. To evaluate the light ...coupling and light trapping, we developed an optical model to simulate the light absorption in the silicon bottom cell. This optical model is an extension of Basore's analytical model. By comparing the simulation with the measurement of the prototype tandem solar cell, we find that the Si bottom cell can gain up to 2.4 mA/cm2 photocurrent by improving light coupling. In addition, we study the impact of the rear surface reflectance on the photocurrent in the Si bottom cell. We observed that ~17% relative increase in current generated in this bottom cell can be achieve by changing the rear surface design from a full area metal contact to a local-back-surface-field configuration.
This paper will provide detail on thin film manufacturing, price and application deployment from 1982, when a-Si entered commercial deployment to 2012. Regional shifts in thin film manufacturing will ...be explored along with aspects and attributes of thin film technologies in competition with crystalline technologies. Included will be brief discussion of the competitive, or, non-competitive attributes of current technology manufacturers as well as those not currently competing. This history will provide a basis for the development of three forecast scenarios to 2017. Forecast assumptions include the low incentive environment in which the photovoltaic industry is currently operating, tender based PPAs and tariffs, macroeconomic factors such as GDP, and effect on thin film technologies of a continued low pricing environment.
We demonstrate a tunable electron-blocking layer to enhance the performance of an Earth-abundant metal-oxide solar-cell material. A 5 nm thick amorphous ternary metal-oxide buffer layer reduces ...interface recombination, resulting in sizable open-circuit voltage and efficiency enhancements. This work emphasizes the importance of interface engineering in improving the performance of Earth-abundant solar cells.
An atomic-layer deposited, tunable amorphous zinc-tin-oxide buffer layer reduces dark saturation current and increases open-circuit voltage and fill-factor in all-metal-oxide thin film solar cells.
We numerically evaluate the device impact of photon re-absorption on InGaP/Si tandem solar cells using a coupled optical-electronic device model. The presented simulation results provide guidelines ...for designing high performance InGaP/Si tandem device. We find that including the effects of photon recycling (PR) and luminescent coupling (LC) results in a 12.5% increase in optimum top-cell thickness for a two-terminal configuration. Furthermore, PR and LC affect the sensitivity of the tandem's conversion efficiency to various device parameters. As the InGaP bulk lifetime increases, there is an absolute efficiency increase of up to 0.7% for the two-terminal as well as the four-terminal configuration. Considering PR and LC furthermore reduces the power generation sensitivity to shunting in the two-terminal configuration. For the four-terminal configuration, photon re-absorption has a less significant impact.
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 84-86).
One of the key ...technological objectives to further decrease the cost of silicon (Si) PV and enable manufacturing of crystalline silicon is to improve the quality of thin, kerfless Si wafers to monocrystalline equivalent. To aid wafer manufacturers to develop high-quality thin Si wafer substrates, performance-limiting defects in the bulk of thin kerfless Si wafers must be identified, and a means to accurately measure the bulk lifetime is necessary. With decreasing wafer thickness, however, the impact of surface recombination increases and dominates the effective lifetime measured by conventional methods. Therefore, the ability to decouple bulk-limited lifetime from surface-limited lifetime is desirable, ideally without the need for surface passivation. Herein, spectrally resolved transient absorption pump-probe spectroscopy and extensive Technology Computer Aided Design simulations are used to decouple the bulk- and surface-limited lifetimes of thin kerfless silicon wafers in a single measurement. A range of sample conditions are studied. It is observed that the technique can successfully provide reasonable upper and lower limits to the bulk and surface recombination parameters for thin kerfless silicon wafers.
by Sin Cheng Siah.
S.M.
PDF
