UNITED SOLAR SYSTEMS CORP Improvement of MultiJunction Solar

UNITED SOLAR SYSTEMS CORP. Improvement of Multi-Junction Solar Cells with nc-Si: H Middle and Bottom Cell Baojie Yan, Guozhen Yue, Gautam Ganguly, Jeffrey Yang and Subhendu Guha United Solar Ovonic Corporation Troy, Michigan, USA This work supported by the National Renewable Energy Laboratory under Thin-Film Partnership Program

UNITED SOLAR SYSTEMS CORP. OUTLINE • What had been achieved before last team meeting • New Results 1. nc-Si: H single-junction solar cells on small-area substrate 2. a-Si: H/a-Si. Ge: H/nc-Si: H triple-junction cells on small-area substrate 3. a-Si: H/nc-Si: H triple-junction cells on small-area substrate 4. a-Si: H/nc-Si: H double-junction cells on large-area substrate • Summary

Key results achieved in last team meeting 1. 2. 3. 4. 8. 4% initial and 8. 2% stable active-area efficiency for a nc-Si: H single-junction cell made with MVHF at 5 -8 Å/s. 13. 1% initial and 11. 5% stable active-area efficiency for an a-Si: H/nc -Si: H double-junction structure made with MVHF at 5 -8 Å/s. 14. 6% initial and 12. 6% stable active-area efficiency for an a-Si: H/a. Si. Ge: H/nc-Si: H triple-junction structure made with RF at 1 Å/s. 9. 5% stable aperture-area (420 cm 2) efficiency for an encapsulated a. Si: H/nc-Si: H double-junction structure made with RF at 1 Å/s.

UNITED SOLAR SYSTEMS CORP. Key techniques for improving MVHF nc-Si: H solar cells Higher pressure and high power • • Increase the deposition rate Reduce the ion bombardment under high pressure Smaller spacing between the cathode and substrate • • • For stable plasma at a given power For uniformity To reduce the powder formation Hydrogen Dilution Profiling • • To control the material structure evolution To keep the structure close to the amorphous/ nanocrystalline transition

UNITED SOLAR SYSTEMS CORP. nc-Si: H single-junction solar cells used as the middle cell In a-Si: H/nc-Si: H triple-junction structure Initial and stable active-area performances of nc-Si: H single-junction cells made with MVHF at high rates.

UNITED SOLAR SYSTEMS CORP. Initial (a) J-V characteristics and (b) quantum efficiency of the best nc-Si: H single-junction solar cell using MVHF.

UNITED SOLAR SYSTEMS CORP. nc-Si: H single-junction solar cells used as the bottom cell in triple-junction structure Initial and stable active-area performances of nc-Si: H single-junction cells made with MVHF at high rates.

UNITED SOLAR SYSTEMS CORP. Initial (a) J-V characteristics and (b) quantum efficiency of a MVHF nc-Si: H single-junction solar cell with high current.

UNITED SOLAR SYSTEMS CORP. a-Si: H middle cells J-V characteristics of a-Si. Ge: H middle cells on SS substrate. The J-V measurements were made under an AM 1. 5 solar simulator with a 530 -nm long pass filter with QE calibration for the Jsc.

UNITED SOLAR SYSTEMS CORP. Current status of a-Si: H/a-Si. Ge: H/nc-Si: H triple-junction cells Initial and stable active-area performances of a-Si: H/a-Si. Ge: H/nc-Si: H triple-junction cells made with RF and MVHF.

UNITED SOLAR SYSTEMS CORP. (a) J-V characteristics and (b) quantum efficiency of an a-Si: H/a-Si. Ge: H/nc-Si: H triplejunction solar cell, where the a-Si: H top and a-Si. Ge: H middle cells were made using RF glow discharge at a low rate and the nc-Si: H bottom cell made with MVHF at a high rate.

UNITED SOLAR SYSTEMS CORP. Current status of a-Si: H/nc-Si: H triple-junction cells Initial and stable active-area performances of a-Si: H/nc-Si: H triplejunction cells.

UNITED SOLAR SYSTEMS CORP. Initial (a) J-V characteristics and (b) quantum efficiency of the best a-Si: H/nc-Si: H triple-junction solar cell.

UNITED SOLAR SYSTEMS CORP. RF nc-Si: H single-junction cells on large area substrate (14 × 15 in 2). The nc-Si: H intrinsic layer was deposited in 50 minutes.

UNITED SOLAR SYSTEMS CORP. RF a-Si: H/nc-Si: H double-junction cells on large area substrate (14 × 15 in 2). The nc-Si: H intrinsic layer in the bottom cell was deposited in 50 minutes.

UNITED SOLAR SYSTEMS CORP. Uniformity of an a-Si: H/nc. Si: H doublejunction cells over an area of larger than 400 cm 2

UNITED SOLAR SYSTEMS CORP. (Left) picture of an encapsulated a-Si: H/nc-Si: H double-junction cell with an aperture area of 420 cm 2 and (right) its AM 1. 5 I-V characteristics.

UNITED SOLAR SYSTEMS CORP. Stable performance of a-Si: H/nc-Si: H double-junction cells measured at United Solar and NREL

Progress in the optimization of multi-junction solar cells with nc-Si: H in the bottom cell.

SUMMARY • • 8. 99% initial and 8. 50% stable active-area efficiency for a nc-Si: H single-junction cell made with MVHF at 5 -8 Å/s 15. 1% initial active-area efficiency for an a-Si: H/a-Si. Ge: H/nc-Si: H triple-junction structure, where the top and the middle cells were made with RF at a low rate, the bottom cell with MVHF at a high rate 14. 1% initial and 13. 2% stable active-area efficiency for an a-Si: H/nc-Si: H triple-junction structure, where the top were made with RF at a low rate, the middle and bottom cell with MVHF at a high rate 9. 5% stable aperture-area (420 cm 2) efficiency for an encapsulated a. Si: H/nc-Si: H double-junction structure.