Properties of Cu(In,Ga) Thin Films and Solar Cells Deposited by Hybrid Process

S Marsillac,H Khatri,K Aryal,R.W Collins

doi:10.1155/2012/385185

Abstract

Cu(In,Ga)Se2solar cells were fabricated using a hybrid cosputtering/evaporation process, and efficiencies as high as 12.4% were achieved. The films were characterized by energy-dispersive X-ray spectroscopy, glancing incidence X-ray diffraction, scanning electron microscopy, auger electron spectroscopy, and transmittance and reflectance spectroscopy, and their properties were compared to the ones of films deposited by coevaporation. Even though the films were relatively similar, the ones deposited by the hybrid process tend to have smaller grains with a slightly preferred orientation along the (112) axis and a rougher surface. Both types of films have uniform composition through the depth. Characterization of these films by variable angle of incidence spectroscopic ellipsometry allowed for the calculation of the position of the critical points, via calculation of the second derivative of the dielectric function and fit with critical points parabolic band oscillators. The solar cells were then characterized by current-voltage and quantum efficiency measurements. An analysis of the diode parameters indicates that the cells are mostly limited by a low fill factor, associated mostly with a high diode quality factor () and high series resistance ( ) .

Highlights

Many technology options exist nowadays to harvest the power of the sun, a sustainable energy source, and generate electricity directly from this source via the photovoltaic effect
The elemental composition of the films was determined by energy dispersive X-ray spectroscopy (EDS)
Glancing incidence X-ray diffraction (GIXRD) measurements were performed using CuKα-radiation (λ = 0.15418 nm) with a 0.01◦ step size and various incidence angles ranging from 0.5◦ to 10◦

Summary

Introduction

Many technology options exist nowadays to harvest the power of the sun, a sustainable energy source, and generate electricity directly from this source via the photovoltaic effect. Results for high-performance Cu(In,Ga)Se2 solar cells have been reported with absorber material prepared either by multisource coevaporation of the elements (Cu, In, Ga, and Se) at temperatures between 550–600◦C or by selenization of Cu, In, and Ga films in the presence of H2Se gas [1,2,3,4,5,6,7]. These techniques are currently implemented in companies such as Wurth Solar, Global Solar, or Solar Frontier. We will present results on the hybrid deposition and characterization of Cu(In,Ga)Se2 thin films and solar cells and will compare these results with those from solar cells in which the Cu(In,Ga)Se2 is purely coevaporated

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Conclusion