# Presentation: 502977

## UNITED SOLAR SYSTEMS CORP.

***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.

***UNITED SOLAR SYSTEMS CORP.***

_**OUTLINE**_
** ****What had been achieved before last team meeting**
** ****New Results**
-  nc-Si:H single-junction solar cells on small-area substrate
-  a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells on small-area substrate
-  a-Si:H/nc-Si:H/nc-Si:H triple-junction cells on small-area substrate
-  a-Si:H/nc-Si:H double-junction cells on large-area substrate
** ****Summary**

**Key results achieved in last team meeting**
- 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-SiGe:H/nc-Si:H triple-junction structure made with RF at 1 Å/s.

## UNITED SOLAR SYSTEMS CORP.

***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.

***UNITED SOLAR SYSTEMS CORP.***

**nc-Si:H single-junction solar cells used as the middle cell**
**In a-Si:H/nc-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.

***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.

***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.

***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.

***UNITED SOLAR SYSTEMS CORP.***

**a-Si:H middle cells**

- J-V characteristics of a-SiGe:H middle cells on SS substrate.  The J-V measurements were made under an AM1.5 solar simulator with a 530-nm long pass filter with QE calibration for the Jsc.** **

## UNITED SOLAR SYSTEMS CORP.

***UNITED SOLAR SYSTEMS CORP.***

**Current status of a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells**

**Initial and stable active-area performances of a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells made with RF and MVHF.**

## UNITED SOLAR SYSTEMS CORP.

***UNITED SOLAR SYSTEMS CORP.***

- (a) J-V characteristics and (b) quantum efficiency of an a-Si:H/a-SiGe:H/nc-Si:H triple-junction solar cell, where the a-Si:H top and a-SiGe: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.

***UNITED SOLAR SYSTEMS CORP.***

**Current status of a-Si:H/nc-Si:H/nc-Si:H triple-junction cells **

**Initial and stable active-area performances of a-Si:H/nc-Si:H/nc-Si:H triple-junction cells.**

## UNITED SOLAR SYSTEMS CORP.

***UNITED SOLAR SYSTEMS CORP.***

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

## UNITED SOLAR SYSTEMS CORP.

***UNITED SOLAR SYSTEMS CORP.***

- RF nc-Si:H single-junction cells on large area substrate (14 ×15 in2). The nc-Si:H intrinsic layer was deposited in 50 minutes.

## UNITED SOLAR SYSTEMS CORP.

***UNITED SOLAR SYSTEMS CORP.***

- RF a-Si:H/nc-Si:H double-junction cells on large area substrate (14 ×15 in2). The nc-Si:H intrinsic layer  in the bottom cell was deposited in 50 minutes.

## UNITED SOLAR SYSTEMS CORP.

***UNITED SOLAR SYSTEMS CORP.***

- Uniformity of an a-Si:H/nc-Si:H double-junction cells over an area of larger than 400 cm2

## UNITED SOLAR SYSTEMS CORP.

***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 AM1.5 I-V characteristics.**

## UNITED SOLAR SYSTEMS CORP.

***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-SiGe: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/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 cm2) efficiency for an encapsulated a-Si:H/nc-Si:H  double-junction structure.