Na‐Diffusion Enhanced p‐type Conductivity in Cu(In,Ga)Se₂: A New Mechanism for Efficient Doping in Semiconductors

Abstract

A new mechanism responsible for the hole concentration increase in the CIGS thin films after Na doping is proposed. At high temperature, a high concentration of Na is doped into the grains. After cooling and water rinsing, the solubility of Na becomes lower, so Na diffuses out of the grains with high concentration of Cu vacancies and hole carriers formed.

Alkali Atoms Diffusion Mechanism in CuInSe2 Explained by Kinetic Monte Carlo Simulations

“…The vacancymediated diffusion of Na has a larger migration barrier than those of K and Rb, whereas interstitial Na (Na i ) atoms diffuse faster than heavier AM in the interstitial site. It was suggested by Yuan et al [44] that the outdiffusion of Na and K atoms from the absorber layer could be the reason for the enhancement of hole concentration. [39] In addition, the presence of Na atoms in the grain interior (GI) indicates the high mobility of Na atoms (Na interstitial diffusion).…”

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

“…From computational studies 29,30 , the capture of Na by V Cu and formation of sodium on copper (Na Cu ) antisite defects in CIGS seems thermodynamically favourable, even considering the most recent Na Cu formation energies calculated with a more reasonable Na electrochemical potential 31,32 . However, it is well known that Na segregates mostly to grain boundaries 33–35 .…”

Role of surface microstructure of Mo back contact on alkali atom diffusion and Ga grading in Cu(In,Ga)Se2 thin film solar cells

“…[12][13][14][15][16][17] The most common approach for the incorporation of alkali atoms in CIGS layer was their natural diffusion from SLG substrate which contained Na and sometimes also K. 18,19 The incorporation of alkali atoms could greatly enhance both the structural and the electrical properties of CIGS absorber materials in comparison with the sodium-free glass. [12][13][14][15][16][17] The most common approach for the incorporation of alkali atoms in CIGS layer was their natural diffusion from SLG substrate which contained Na and sometimes also K. 18,19 The incorporation of alkali atoms could greatly enhance both the structural and the electrical properties of CIGS absorber materials in comparison with the sodium-free glass.…”

“…19,21,22 However, excessive Na diffusion from the SLG substrate not only hindered the grain size of CIGS film but also degraded its electrical property as well as the device performances with higher defect density. 16 Very recently, some researchers have conducted an oxidation treatment to their Mo back contact films prior to CIGS deposition and believed that MoO 3 on the surface of Mo back contact plays a key role by reacting with alkali cations from glass and releasing them towards CIGS film upon an alkali concentration difference. 16 Very recently, some researchers have conducted an oxidation treatment to their Mo back contact films prior to CIGS deposition and believed that MoO 3 on the surface of Mo back contact plays a key role by reacting with alkali cations from glass and releasing them towards CIGS film upon an alkali concentration difference.…”