Download or read book Characterization of Photocurrent and Voltage Limitations of Copper(indium, Gallium)selenide Thin-film Polycrystalline Solar Cells written by Christopher P. Thompson and published by ProQuest. This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thin film polycrystalline CdS/Cu(In, Ga)(Se, S) 2 solar cells have great potential as a candidate for high efficiency, high throughput, low cost production. Cu(In, Ga)Se 2 devices have laboratory efficiencies approaching 20% and module efficiencies around 11%. However, most progress in device optimization has been the result of empirical studies; little is known about the device defect structure, and even less is known about the control of defects within the Cu(In, Ga)(Se, S) 2 absorber. Despite years of study, the complex nature of the Cu(In, Ga)(Se, S) 2 system has made progress towards a fundamental understanding of device behavior, and limiting defects a slow affair. The goal of this work is to shed further light on the nature of the limitations on photocurrent and voltage. The main topics covered in this thesis are: (1) fitting quantum efficiency curves calculated from an analytical model to measured quantum efficiency curves, and (2) Open circuit voltage temperature measurements. For the first section, series of devices with varying absorber layers will be analyzed, using the minority carrier diffusion length as the only fitting parameter. All other variables within the model will be supplied from direct and indirect measurements. We show that by using quantum efficiency, capacitance-voltage, and current-voltage measurements, we can generate excellent fits using only diffusion length as a fitting parameter. It is found that for Cu(In, Ga)Se 2 devices with E G [approximate]1.2eV, L=1000-1500nm.; for wide bandgap devices, with E G [approximate]1.4eV, L=10-400nm; for devices with E G [approximate]1.2eV, deposited with a low substrate temperature, L=650nm. Wide bandgap devices long wavelength collection is limited by minority carrier diffusion. For the second section, V OC (T) measurements are taken on devices with a wide range of absorbers, including some previously un-measured devices; absorbers grown with a Na deficiency. Analysis will focus on the activation energy of the dominant recombination mechanism, as well as low temperature saturation of V OC . Both of these parameters shed light on the limiting properties of devices. Cu(In, Ga)Se 2 with bandgap ranging from 1.2eV-1.4eV are limited by Shockley Read Hall recombination, and have a ratio of saturation voltage to bandgap of 80%. Lowering the electrical quality of the absorber by depositing the Cu(In, Ga)Se 2 layer at lower substrate temperature decreases the ratio of saturation voltage to bandgap to 64%, as a result of increased bandtail defect states. CuInS 2 devices and Cu(In, Ga)Se 2 devices with low or no Na are limited by hetero-interface recombination, and have a saturation voltage to bandgap ratio of ~60%.