Fabrication of Robust Nanoscale Contact between a Silver Nanowire Electrode and CdS Buffer Layer in Cu(In,Ga)Se2 Thin-film Solar Cells

Summary

In this protocol, we describe the detailed experimental procedure for the fabrication of a robust nanoscale contact between a silver nanowire network and CdS buffer layer in a CIGS thin-film solar cell.

Abstract

Silver nanowire transparent electrodes have been employed as window layers for Cu(In,Ga)Se₂ thin-film solar cells. Bare silver nanowire electrodes normally result in very poor cell performance. Embedding or sandwiching silver nanowires using moderately conductive transparent materials, such as indium tin oxide or zinc oxide, can improve cell performance. However, the solution-processed matrix layers can cause a significant number of interfacial defects between transparent electrodes and the CdS buffer, which can eventually result in low cell performance. This manuscript describes how to fabricate robust electrical contact between a silver nanowire electrode and the underlying CdS buffer layer in a Cu(In,Ga)Se₂ solar cell, enabling high cell performance using matrix-free silver nanowire transparent electrodes. The matrix-free silver nanowire electrode fabricated by our method proves that the charge-carrier collection capability of silver nanowire electrode-based cells is as good as that of standard cells with sputtered ZnO:Al/i-ZnO as long as the silver nanowires and CdS have high-quality electrical contact. The high-quality electrical contact was achieved by depositing an additional CdS layer as thin as 10 nm onto the silver nanowire surface.

Introduction

Silver nanowire (AgNW) networks have been extensively studied as an alternative to indium tin oxide (ITO) transparent conducting thin films due to their advantages over conventional transparent conducting oxides (TCOs) in terms of lower processing cost and better mechanical flexibility. Solution-processed AgNW network transparent conducting electrodes (TCEs) have thus been employed in Cu(In,Ga)Se₂ (CIGS) thin-film solar cells^1,2,3,4,5,6. Solution-processed AgNW ....

Protocol

1. Preparation of Mo-coated glass by DC magnetron sputtering

1. Load cleaned glass substrates into a DC magnetron and pump down to below 4 x 10^-6 Torr.
2. Flow Ar gas and set the working pressure to 20 mTorr.
3. Turn on plasma and increase the DC output power to 3 kW.
4. After pre-sputtering of 3 min for target cleaning, begin the Mo deposition until the Mo film thickness reaches approximately 350 nm.
5. Set the working pressure to 15 mTorr while maintaining the same output power (i.e., 3 kW).
6. Resume the Mo deposition until the total thickness of Mo reaches approximately 750 nm.

Results

The layer structures of the CIGS solar cells with (a) standard ZnO:Al/i-ZnO and (b) AgNW TCE are shown in Figure 3. The surface morphology of CIGS is rough, and a nanoscale gap can form between the AgNW layer and the underlying CdS buffer layer. As highlighted in Figure 3A, the 2^nd CdS layer can be selectively deposited onto the nanoscale gap to create a stable electrical contact. The detailed explanation on the format.......

Discussion

Note that the deposition time of the 2^nd CdS layer must be optimized to achieve the optimal cell performance. As the deposition time increases, the thickness of the 2^nd CdS layer increases, and consequently, the electrical contact will improve. However, further deposition of the 2^nd CdS layer will result in a thicker layer that reduces light absorption, and the device efficiency will decrease. We achieved the best cell performance with 10 min of deposition time for the 2^nd CdS .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Mo	Materion	Purity: 3N5	Mo sputtering
Cu	5N Plus	Purity: 4N7	CIGS deposition
In	5N Plus	Purity: 5N	CIGS deposition
Ga	5N Plus	Purity: 5N	CIGS deposition
Se	5N Plus	Purity: 5N	CIGS deposition
Ammonium acetate	Alfa Aesar	11599	CdS reaction solution
Ammonium hydroxide	Alfa Aesar	L13168	CdS reaction solution
Cadmium acetate dihydrate	Sigma-Aldrich	289159	CdS reaction solution
Thiourea	Sigma-Aldrich	T8656	CdS reaction solution
Silver Nanowire	ACSMaterial	AgNW-L30	AgNW dispersion