20%-efficient polycrystalline Cd(Se,Te) thin-film solar cells with compositional gradient near the front junction.

Area of Science:

• Materials Science
• Photovoltaics
• Semiconductor Physics

Background:

• Bandgap engineering is crucial for enhancing solar cell performance.
• Cadmium telluride (CdTe) solar cells are a leading thin-film technology.
• Achieving a bandgap gradient in CdTe cells has been a challenge.

Purpose of the Study:

• To demonstrate the realization of a bandgap gradient in CdTe thin-film solar cells.
• To improve open-circuit voltages (V_OCs) by suppressing recombination.
• To investigate the impact of a novel Cd(O,S,Se,Te) region on device performance.

Main Methods:

• Incorporation of oxygenated cadmium sulfide (CdS) and cadmium selenide (CdSe) layers.
• Formation of a Cd(O,S,Se,Te) region with the same crystal structure as the absorber.
• Utilizing commercial tin oxide (SnO₂) buffer layers.

Main Results:

• Successfully created a bandgap gradient in CdTe solar cells.
• Reduced hole density in the front junction region.
• Introduced a band alignment spike, suppressing nonradiative recombination.
• Achieved improved V_OCs and a champion device efficiency of 20.03% with a V_OC of 0.863 V.

Conclusions:

• The bandgap gradient effectively enhances V_OCs in CdTe solar cells.
• The novel Cd(O,S,Se,Te) region is key to achieving this gradient.
• This approach offers a promising pathway for further improving CdTe photovoltaic technology.