Efficiency enhancement of flexible Cu(In,Ga)Se₂solar cells deposited on polyimide-coated soda lime glass substrate by alkali treatment

Abstract

Alkali treatment effects on Cu(In,Ga)Se2 (CIGS) solar cells deposited on polyimide-coated soda lime glass (PI-coated SLG) were investigated. CIGS on PI-coated SLG shows Na diffusion from the substrate, which should be controlled to obtain high efficiencies. Further incorporation of Na was achieved by enhancing diffusion from the substrate or by external incorporation using post-deposition treatment (PDT) methods. Both methods lead to a high efficiency of approximately 15%. Moreover, aside from Na, K was also incorporated by KF-PDT, resulting in efficiency improvement from 12% for an untreated CIGS to more than 18% at the maximum substrate temperature of 450 °C, which is comparable to CIGS deposited at higher temperatures using the same equipment. It was also found that the alkali concentration of CIGS deposited on PI-coated SLG shows almost the same behavior as that of a film deposited on a rigid glass, suggesting that the deposition technique for CIGS on the rigid glass can be applied to flexible substrates.

Growth-Promoting Mechanism of Bismuth-Doped Cu(In,Ga)Se2 Solar Cells Fabricated at 400 °C

“…They are both believed to be essential for fabricating a high-performance device. As is widely reported, the incorporation of Na can effectively enhance the carrier concentration because of defect passivation; the incorporation of K can increase the donor defect (Cd Cu + ) density to form the surface inversion layer and decrease the valence band maximum at the absorber surface to reduce the heterojunction interface recombination. ,− Generally, during annealing at an elevated temperature (550 °C), the diffusion amount of alkali metal ions from the SLG substrate into the CIGS layer can satisfy the demand of device performance improvement. In this study, alkali metal ions should have been severely inadequate because low temperatures could reduce the thermal diffusion of alkali metal ions from the SLG substrate into the CIGS layer.…”

A Study of Doping Profile for the Site Selectively Zn‐Doped p‐type Cu(In,Ga)Se2 Thin Film for Solar Cell

“…Recently, the post deposition treatment (PDT) with alkaline element such as Na, K, Rb, and Cs, greatly enhances η . This improvement is considered to be due to the increase of carrier concentration in the CIGS absorber . At present, the intentionally undoped CIGS film used for the solar cell has carrier concentration p of 10 15 ≈ 10 16 cm −3 .…”