Transparent Electrode and Buffer Layer Combination for Reducing Carrier Recombination and Optical Loss Realizing over a 22%-Efficient Cd-Free Alkaline-Treated Cu(In,Ga)(S,Se)2 Solar Cell by the All-Dry Process

Jakapan Chantana; Yu Kawano; Takahito Nishimura; Yoshinori Kimoto; Takuya Kato; Hiroki Sugimoto; Takashi Minemoto

doi:10.1021/acsami.0c01980

Transparent Electrode and Buffer Layer Combination for Reducing Carrier Recombination and Optical Loss Realizing over a 22%-Efficient Cd-Free Alkaline-Treated Cu(In,Ga)(S,Se)₂ Solar Cell by the All-Dry Process

ACS Appl Mater Interfaces. 2020 May 13;12(19):22298-22307. doi: 10.1021/acsami.0c01980. Epub 2020 May 4.

Authors

Jakapan Chantana^{1

2}, Yu Kawano¹, Takahito Nishimura³, Yoshinori Kimoto⁴, Takuya Kato⁴, Hiroki Sugimoto⁴, Takashi Minemoto¹

Affiliations

¹ Department of Electrical and Electronic Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan.
² Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan.
³ Ritsumeikan Global Innovation Research Organization, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan.
⁴ Atsugi Research Center, Advanced Technology Research Laboratories, Idemitsu Kosan Co., Ltd., Atsugi, Kanagawa 243-0206, Japan.

PMID: 32320201
DOI: 10.1021/acsami.0c01980

Abstract

The structures of K or Cs alkaline-treated Cu(In,Ga)(S,Se)₂ (CIGSSe) solar cells are developed, and their carrier recombination rates are scrutinized. It is determined that short-circuit current density (J_SC) is enhanced (decreased optical loss), when ZnS(O,OH), (Cd,Zn)S, and Zn_0.8Mg_0.2O buffers with a large band gap energy (E_g) are applied as a replacement of CdS buffer. The J_SC is further increased, reducing the optical loss more, when Zn_0.9Mg_0.1O:B is used as the transparent conductive oxide (TCO) with a larger E_g and lower free carrier absorption than those of ZnO:Al. Furthermore, all carrier recombination rates throughout the devices with K or Cs treatment, especially at the buffer/absorber interface and in the quasi neutral region, are reduced, thereby reducing open-circuit voltage deficit (V_OC,def), well consistent with the simulated ones. The carrier recombination rate at the buffer/absorber interface is further decreased, when the CdS and (Cd,Zn)S buffers, deposited by chemical bath deposition, are applied, leading to the greater reduction of the V_OC,def and the high conversion efficiency (η) of about 21%. Under the trade-off between V_OC,def and optical loss, the highest η of 22.6% is attained with the lowest power loss (or the highest V_OC × J_SC) in the Cs-treated Cd-free CIGSSe solar cell with an optimized structure of glass/Mo/CIGSSe/Zn_0.8Mg_0.2O/Zn_0.9Mg_0.1O:B, fabricated by the all-dry process, where the Zn_0.8Mg_0.2O buffer is prepared by the sputtering method. This occurs because the J_SC is the highest attributable to the larger E_g of Zn_0.8Mg_0.2O buffer than those of the CdS and (Cd,Zn)S.

Keywords: (Cd,Zn)S; Cu(In,Ga)(S,Se)2 thin-film solar cell; Zn1−xMgxO; Zn1−xMgxO:Al; Zn1−xMgxO:B; carrier recombination rates.