Preparation of CIGS Absorber Layer in Thin Film Solar Cells

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This tutorial outlines the key steps and considerations for preparing a high-quality copper indium gallium selenide (CIGS) absorber layer, which is critical for efficient thin film solar cells.

Author Julissa Green | Last edit 30/05/2025 by JulissaGreen

Difficulty

Hard

Duration

1 day(s)

Introduction

This tutorial provides a comprehensive, step-by-step guide on preparing the copper indium gallium selenide (CIGS) absorber layer, a critical component in thin film solar cells. It covers the sequential processes of magnetron sputtering to deposit Cu/In and CuInGa films with precise elemental control, followed by chemical vapor deposition (CVD) selenization to form the final CIGS absorber layer. The tutorial emphasizes the importance of controlling elemental ratios, especially the Cu/In and Ga/In proportions, to optimize film morphology, crystallinity, and photovoltaic performance. It also highlights practical considerations such as using solid selenium powder instead of toxic H2Se gas for safer and cost-effective selenization.

Materials

High-purity copper (Cu), indium (In), and gallium (Ga) sputtering targets
Solid-state selenium powder (or H2Se gas if available)
Substrate materials (e.g., glass or molybdenum-coated glass)
Inert gases (argon) for sputtering atmosphere

Tools

Magnetron sputtering system with co-sputtering capability
Chemical vapor deposition (CVD) furnace/system with temperature control
Oven or heating stage for selenization
Characterization instruments (X-ray diffraction, SEM, etc.)
Safety equipment for handling selenium and sputtering targets

Step 1 - Preparation of Cu/In Film by Magnetron Sputtering

Use co-sputtering to simultaneously deposit copper-indium (Cu/In) alloy and indium (In) elemental targets in the same sputtering chamber.
Precisely control the Cu/In elemental ratio, as it strongly influences film properties and solar cell performance.
Morphology varies with composition: Cu-rich films have a metallic luster and mirror-like surface, while In-rich films appear dark red with smaller grain sizes.
In-rich films are preferred as precursors because their small grain size facilitates better crystallization and smooth morphology after selenization, forming high-quality CIS and CIGS films.

Step 2 - Preparation of CuInGa Film by Magnetron Sputtering

Substitute a portion of indium (In) with gallium (Ga) in the CuInSe2 film to tune the band gap from 1.04 eV to 1.68 eV, optimizing solar cell efficiency.
Control Ga content carefully: high Ga concentrations can cause film cracking and formation of Cu1-xSe heterophases, which degrade electrical properties.
Optimal solar cell performance is achieved when Ga replaces about 30% of In. This balance minimizes cracking and maintains good electron transport, as confirmed by XRD analysis.

Step 3 - Preparation of CIGS Film by Chemical Vapor Deposition (CVD)

Subject the CuInGa precursor film to a two-step selenization process in a CVD system to form the final CIGS absorber layer.
Use solid-state selenium powder as a safer and cost-effective alternative to toxic H2Se gas.
The first selenization step vaporizes selenium to create a high selenide vapor concentration.
The second step thermally selenizes the alloy film, with temperature playing a critical role in film crystallinity and quality.

Notes and references

“Preparation of CIGS Absorber Layer.” Sputter Targets, Stanford Advanced Materials, www.sputtertargets.net/preparation-of-copper-indium-gallium-selenide-absorber-layer. Accessed 30 May 2025.
Green, Julissa. “An Introduction to CIGS Thin-Film Photovoltaics.” Sputter Targets, Stanford Advanced Materials, www.sputtertargets.net/blog/an-introduction-to-cigs-thin-film-photovoltaics.html. Accessed 30 May 2025.