# Presentation: 130985

## High Efficiency CIGS Thin Film Solar Cells: Laboratory Perspective

**K. Ramanathan, R. Dhere, J. Keane, B. To, R. Bhattacharya, M. Contreras, and R. Noufi**
**National Center for Photovoltaics, NREL**

**2005 SETP Review Meeting, Denver, CO**

## Introduction

**CIS thin-film PV is a success story**
**Fine example of moving R&D work to commercialization**
**Concerted effort is still needed:**
**Increase efficiency in all systems**
**Simplify device structures**
**Understand electronic effects at interfaces**
**Simplify deposition processes to increase speed, reduce cost**

## Outline

**High Efficiency CIGS Solar Cells**
**Thin CIGS cells**
**Low Temperature Deposition**
**Deposition from Low Purity Sources**
**Conclusions**

## Standard Cell Structure

**ZnO**

**CdS, 50 nm**

**CIGS, 2.5 μm**

**Mo, 0.8 μm **

**Float Glass**

## High Efficiency Solar Cells

## Towards Twenty

**Towards Twenty**

## CIGS Solar Cells with Eg=1.1-1.2 eV

- 26% Ga/(In+Ga)

- 31% Ga/(In+Ga)

## * Uncertainty is 3% of absolute value

| Bandgap (eV) | Voc (V) | Jsc (mA/cm2) | Fill Factor (%) | Efficiency* (%) |
| --- | --- | --- | --- | --- |
| 1.10 | 0.701 | 34.60 | 79.65 | 19.3 |
| 1.12 | 0.704 | 34.33 | 79.48 | 19.2 |

| 1.22 | 0.740 | 31.72 | 78.47 | 18.4 |
| --- | --- | --- | --- | --- |
| 1.21 | 0.737 | 31.66 | 78.08 | 18.2 |

| 1.15 | 0.720 | 32.86 | 80.27 | 19.0 |
| --- | --- | --- | --- | --- |
| 1.17 | 0.731 | 31.84 | 80.33 | 18.7 |

## Efficiency vs. CIGS Bandgap

**Efficiency vs. CIGS Bandgap**

## A decade of collaboration

**N****a**** higher, N****t**** lower than other materials**

**Cell Level Stability: Unchanged**
**Transient Effects: Negligible**
**Band gap grading: Ongoing**

**Electronic processes at the junction:**
**Cd PE, Zn doped junctions **

## Thin CIGS Solar Cells

## Thin CIGS Solar Cells

**Indium availability and price are  concerns for CIS PV.**
**Began work to fabricate solar cells on thinner (≤1 μm) absorbers grown by modified 3-stage process.**
**Thin absorbers also fabricated using co-deposition of all elements.**

## 1-μm thick absorbers

**1-μm thick absorbers**

**3-stage**

**Co-deposition**

**V****oc****= 0.654 V; **
**J****sc****= 31.6 mA/cm****2**
**FF= 78.3%; Eff = 16.2%**

**V****oc****= 0.699 V; **
**J****sc****= 30.6 mA/cm****2**
**FF= 75.4%; Eff = 16.1%**

## Thinner Absorbers

**0.75 μm (12.5%)**

**0.4 μm (9.1%)**

## QE

## 0.4 μm cell - Optical

**0.4 μm cell - Optical**

## Latest Result for 1 μm

**Latest Result for 1 μm**

## Thin Cells Summary

| t (μm) | Voc (V) | Jsc (mA/cm2) | FF (%) | Eff (%) |
| --- | --- | --- | --- | --- |
| 1.0 (3 stg) | 0.678 | 31.9 | 79.2 | 17.15 |
| 1.0 (codep) | 0.699 | 30.6 | 75.4 | 16.0 |
| 0.75 | 0.652 | 26.0 | 74.0 | 12.5 |
| 0.40 | 0.565 | 21.3 | 75.7 | 9.1 |
| 1.4 (450 ̊C) | 0.585 | 31.1 | 70.6 | 12.9 |

**Thin Cells Summary**

## Growth from Low Purity Metals

## Working with

**low purity metals**

**Substantial savings if one can use 3N or 4N purity metals (In, Ga). 10-20% @ 100 MW level**
**II-VI and I-III-VI****2**** compounds appear to be tolerant to extrinsic impurities (exceptions Cd, Zn, halogens in CIGS)**
**Impurities may not evaporate, incorporate or be electrically active**

## Sodalime silicate glass has plenty of impurities!

**Sodalime silicate glass has plenty of impurities!**
**SiO****2****	****	****72.8%**
**Na****2****O****	****	****12.7**
**CaO****	****	****8.1**
**MgO****	****	****3.8**
**Al****2****O****3****	****	****1.4**
**K****2****O****	****	****0.8**
**Other (Fe)****	****0.4**

## Fe, Pb, Cd, Zn, Sn present in the 0.1% of low purity metals.

| Process
Condition | Voc 
(V) | Jsc (mA/cm2) | FF (%) | Eff (%) |
| --- | --- | --- | --- | --- |
| 99.999% | 0.671 | 33.1 | 77.3 | 17.1 |
| 99.9% | 0.624 | 34.5 | 72.1 | 15.5 |

**Fe, Pb, Cd, Zn, Sn present in the 0.1% of low purity metals.**
**Exact amounts in the film to be determined.**

## Demonstrated high efficiency CIGS solar cells with high Voc and fill factors. Efficiency ≥ 19% for Eg of 1.15–1.2 eV.
Presented new results on thin CIGS solar cells made by three-stage process and co-deposition. 17% efficiency at 1 μm, 9% at 0.4 μm.
Processing at lower temperatures, low purity metals appear promising.

**Presented new results on thin CIGS solar cells made by three-stage process and co-deposition. 17% efficiency at 1 μm, 9% at 0.4 μm.**
**Processing at lower temperatures, low purity metals appear promising.**

**Conclusions**

## F.S. Hasoon
J. Dolan
G. Teeter
T. Moriarty
X. Wu

**J. Dolan**
**G. Teeter**
**T. Moriarty**
**X. Wu**

**Acknowledgments**

**T.J. Coutts**
**H.S. Ullal**
**B. von Roedern**
**K. Zweibel**
**D. Tarrant**