Hall effect measurements on Bridgman-grown CuInSe2 with sodium
H F Myers1, C H Champness, I Shih
1Department of Electrical and Computer Engineering, McGill University, Montreal, QC, Canada.
Nanotechnology
|March 9, 2010
Summary
Sodium addition to copper indium selenide (CIS) monocrystals did not significantly alter electrical properties. However, slight decreases in hole concentration were observed with excess selenium and sodium, suggesting potential roles for grain boundaries in photovoltaic device performance.
Area of Science:
- Materials Science
- Solid-State Physics
- Photovoltaics
Background:
- Sodium incorporation enhances polycrystalline Cu(In,Ga)Se2 and CuInSe2 solar cells.
- Sodium is typically found at grain boundaries, not within crystal grains, implying grain boundary influence.
Purpose of the Study:
- To investigate the effect of sodium on the properties of large monocrystals of CuInSe2.
- To understand sodium's role in photovoltaic performance by studying bulk material properties.
Main Methods:
- Grew CuInSe2 monocrystals using the vertical-Bridgman method with varying sodium content.
- Introduced excess selenium to simulate cell fabrication conditions.
- Performed resistivity and Hall effect measurements on the grown crystals.
Main Results:
- No significant changes in resistivity or majority hole concentration were observed.
- A slight decrease in hole concentration was noted in excess selenium samples with 0.2-0.3 at.% sodium.
- Hole mobility showed no clear trend, but increased with 0.2 at.% sodium addition in both sample types.
Conclusions:
- Sodium's impact on bulk CuInSe2 properties is minimal under these conditions.
- The performance enhancement in polycrystalline cells likely stems from sodium's interaction with grain boundaries, not bulk effects.
- Further research into grain boundary phenomena is warranted.
