Carbon-Impurity Affected Depth Elemental Distribution in Solution-Processed Inorganic Thin Films for Solar Cell...

Area of Science:

• Materials Science
• Renewable Energy
• Thin Film Technology

Background:

• Nonvacuum solution-based fabrication of inorganic thin films like copper indium gallium diselenide (CISe) commonly results in a doubled-layered structure.
• This structure includes a top dense inorganic film and a bottom carbon-containing residual layer.
• The role of this carbon layer in device performance, particularly regarding series resistance, is debated.

Purpose of the Study:

• To investigate the precise influence of the carbon residual layer on the performance of CISe solar cells.
• To clarify the contradictory views on whether the carbon layer limits device efficiency.

Main Methods:

• Utilized copper indium gallium diselenide (CISe) as a model system for experimental analysis.
• Analyzed the impact of varying carbon content on elemental distribution and film morphology during selenization.
• Fabricated and tested CISe solar cells with precursor films containing different amounts of carbon.

Main Results:

• Experimental evidence indicates the carbon residual layer is electrically benign.
• Carbon selectively hinders copper diffusion during selenization, affecting the top CISe layer's composition (Cu-deficient) and improving film morphology.
• Optimal carbon content in precursor films led to high CISe solar cell efficiencies up to 9.15%.

Conclusions:

• The carbon residual layer's impact on device efficiency is indirect, mediated through its influence on film composition and morphology.
• Controlling the intermediate amount of carbon in precursor films is crucial for optimizing CISe solar cell performance.
• The findings challenge the notion of the carbon layer solely as an efficiency-limiting factor.