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Title: Application of photoluminescence imaging and laser-beam-induced-current mapping in thin film solar cell characterization

Abstract

My research projects are focused on application of photonics, optics and micro- fabrication technology in energy related fields. Photonic crystal fabrication research has the potential to help us generate and use light more efficiently. In order to fabricate active 3D woodpile photonic structure devices, a woodpile template is needed to enable the crystal growth process. We developed a silica woodpile template fabrication process based on two polymer transfer molding technique. A silica woodpile template is demonstrated to work with temperature up to 900 C. It provides a more economical way to explore making better 3D active woodpile photonic devices like 3D photonic light emitting diodes (LED). Optical research on solar cell testing has the potential to make our energy generation more e cient and greener. PL imaging and LBIC mapping are used to measure CdTe solar cells with different back contacts. A strong correlation between PL image defects and LBIC map defects is observed. This opens up potential application for PL imaging in fast solar cell inspection. 2D laser IV scan shows its usage in 2D parameter mapping. We show its ability to generate important information about solar cell performance locally around PL image defects.

Authors:
 [1]
  1. Iowa State Univ., Ames, IA (United States)
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1417978
Report Number(s):
IS-T 3207
DOE Contract Number:
AC02-07CH11358
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 14 SOLAR ENERGY

Citation Formats

Liu, Geyuan. Application of photoluminescence imaging and laser-beam-induced-current mapping in thin film solar cell characterization. United States: N. p., 2017. Web. doi:10.2172/1417978.
Liu, Geyuan. Application of photoluminescence imaging and laser-beam-induced-current mapping in thin film solar cell characterization. United States. doi:10.2172/1417978.
Liu, Geyuan. Sat . "Application of photoluminescence imaging and laser-beam-induced-current mapping in thin film solar cell characterization". United States. doi:10.2172/1417978. https://www.osti.gov/servlets/purl/1417978.
@article{osti_1417978,
title = {Application of photoluminescence imaging and laser-beam-induced-current mapping in thin film solar cell characterization},
author = {Liu, Geyuan},
abstractNote = {My research projects are focused on application of photonics, optics and micro- fabrication technology in energy related fields. Photonic crystal fabrication research has the potential to help us generate and use light more efficiently. In order to fabricate active 3D woodpile photonic structure devices, a woodpile template is needed to enable the crystal growth process. We developed a silica woodpile template fabrication process based on two polymer transfer molding technique. A silica woodpile template is demonstrated to work with temperature up to 900 C. It provides a more economical way to explore making better 3D active woodpile photonic devices like 3D photonic light emitting diodes (LED). Optical research on solar cell testing has the potential to make our energy generation more e cient and greener. PL imaging and LBIC mapping are used to measure CdTe solar cells with different back contacts. A strong correlation between PL image defects and LBIC map defects is observed. This opens up potential application for PL imaging in fast solar cell inspection. 2D laser IV scan shows its usage in 2D parameter mapping. We show its ability to generate important information about solar cell performance locally around PL image defects.},
doi = {10.2172/1417978},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat May 06 00:00:00 EDT 2017},
month = {Sat May 06 00:00:00 EDT 2017}
}

Thesis/Dissertation:
Other availability
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  • The results of experimental measurements and characterization of high efficiency, thin film CuInSe/sub 2//Cd(Zn)S solar cells provided by Boeing are reported. These devices are produced by elemental evaporation; they have very high I/sub SC/ but lower than expected V/sub OC/ and FF. An automated, multi-purpose experimental station was developed which can carry out capacitance, current, spectral response measurements as a function of voltage, frequency, wavelength, light bias intensity and temperature. The device is modeled as a p-i-n heterojunction where the interface largely determines the device properties and transport. Long time constants of capacitance transients were observed as light or voltagemore » bias was changed. From such transient data it is deduced that a bulk deep level hole trap exists in the selenide which has a density nearly the same as the free carrier density. It was also observed that the photocurrent is strongly bias dependent in violation of the superposition principle. It is shown, by using chopped light data of collection efficiency and the dark I-V, that the light diode can be fully explained on the basis of a voltage.« less
  • In an effort to develop a more full characterization tool of shape memory alloys, a new technique is presented for the mechanical characterization of microactuators and applied to SMA thin films. A test instrument was designed to utilize a spring-loaded transducer in measuring displacements with resolution of 1.5 pm and forces with resolution of 0.2 mN. Employing an out-of-plane loading method for freestanding SMA thin films, strain resolution of 30με and stress resolution of 2.5 MPa were achieved. This new testing method is presented against previous SMA characterization methods for purposes of comparison. Four mm long, 2 μm thick NiTiCumore » ligaments suspended across open windows were bulk micromachined for use in the out-of-plane stress and strain measurements. The fabrication process used to micromachine the ligaments is presented step-by-step, alongside methods of fabrication that failed to produce testable ligaments. Static analysis showed that 63% of the applied strain was recovered while ligaments were subjected to tensile stresses of 870 MPa. In terms of recoverable stress and recoverable strain, the ligaments achieved maximum recovery of 700 MPa and 3.0% strain. No permanent deformations were seen in any ligament during deflection measurements. Maximum actuation forces and displacements produced by the 4 mm ligaments situated on 1 cm square test chips were 56 mN and 300 μm, respectively. Fatigue analysis of the ligaments showed degradation in recoverable strain from 0.33% to 0.24% with 200,000 cycles, corresponding to deflections of 90 μm and forces of 25 mN. Cycling also produced a wavering shape memory effect late in ligament life, leading to broad inconsistencies of as much as 35% deviation from average. Unexpected phenomena like stress-induced martensitic twinning that leads to less recoverable stress and the shape memory behavior of long life devices are addressed. Finally, a model for design of microactuators using shape memory alloys is presented to illustrate how results obtained from these tests can be interpreted and applied to the creation of MEMS devices.« less
  • The main goals of this thesis were to compare Cu/sub 2/S/CdS and Cu/sub 2/S/ZnCdS cells using Cu/sub 2/S/CdS cells as a reference, and to understand the operation and properties of Cu/sub 2/S/ZnCdS cells in order to improve cell performance. Four different measurements were used: electric, spectral, capacitance, and deep trap. I-V measurements give important electric parameters of the cells; cell efficiency, fill factor, short-circuit current, open circuit voltage, shunt resistance, and series resistance are reported. Spectral response with and without bias light were measured for both Cu/sub 2/S/CdS and Cu/sub 2/S/ZnCdS cells. White and blue bias light enhance the spectralmore » response, while red bias light quenches the response. This is attributed to ionization and filling of deep traps near the junction. Capacitance measurements on both cell types show that 1/C/sup 2/ versus voltage is quite flat, which indicates the existence of an i-layer (insulation layer) in the CdS or ZnCdS near the junction. Three methods - photocapacitance, space-charge-limited current, and thermally stimulated current techniques - were used for deep trap measurements. Photocapacitance measurements indicate one deep donor energy and two deep acceptor energy levels. These trap energies become larger as the content of Zn in ZnCdS increases.« less
  • Many problems generally associated with heteroepitaxial growth of semiconducting materials were much in evidence. In particular, interfacial diffusion resulting in autodoping of both substrate and the grown epilayer precluded rectifying heterojunction formation for ZnSiAs/sub 2/ layers grown on Ge, GaAs or Si substrate. The lattice mismatch of about three percent between silicon and ZnSiAs/sub 2/ provided additional problems of microcracks in and nonadherence of the epilayers. This other set of problems was rectified by the in-situ growth of a silicon buffer layer just prior to the ZnSiAs/sub 2/ deposition. Blocking heterojunction formation was achieved between vacuum evaporated CdS at aboutmore » 200/sup 0/C and 660/sup 0/C MO-CVD grown ZnSiAs/sub 2/ layers on Ge and Si (with a Si buffer layer). In the latter case a cascade structure resulted with photoresponse characteristics showing additive open circuit voltages for the two junctions. Models have been formulated for the dark-current transport in the n-CdS/ZnSiAs/sub 2/ heterojunctions and the photovoltaic spectral response in p-ZnSiAs/sub 2//n/sup +//p-Si structures. The current transport model envisages a trapping-recombination assisted tunneling mechanism in the heterojunctions. The ZnSiAs/sub 2/ layer plays a passive photo-attenuator role in the spectral response model. Computer simulations give close fit between the theory and experimental observations. Parameters deduced from experimental data and theoretical models include effective trapping density for 77/sup 0/ < T < 300/sup 0/K in the n-CdS/p-ZnSiAs/sub 2/ heterojunctions, carrier concentrations in ZnSiAs/sub 2/ and an electron affinity value for MO-CVD grown ZnSiAs/sub 2/ layer. This is the first time that an experimental value for the electron affinity in ZnSiAs/sub 2/ has been reported.« less