Effect of different alkali (Li, Na, K, Rb, Cs) metals on Cu2ZnSnSe4 solar cells

Publication date: Available online 15 November 2016
Source:Thin Solid Films
Author(s): Aniket Mule, Bart Vermang, M. Sylvester, Guy Brammertz, Samaneh Ranjbar, Thomas Schnabel, Nikhil Gampa, Marc Meuris, Jef Poortmans
It is well established that the addition of sodium (Na) to chalcopyrite or kesterite based solar cells markedly increases the solar cell performance. In this work, we explore the effect of Na and other alkali metals like potassium (K), rubidium, caesium and lithium (Li) – on pure selenide Cu2ZnSnSe4 (CZTSe) solar cells. We demonstrate the deposition of alkali metals using spin coating on e-beam evaporated metal precursors. The stack of metal precursors with alkali layer was then selenised at high temperatures to obtain a good quality CZTSe absorber. The diffusion of alkali metals into the absorber layer was confirmed using glow discharge optical emission spectroscopy. Samples doped with Na or K have shown improvement in the open circuit voltage. A maximum power conversion efficiency of 8.3% (without anti-reflection coating) and a top open circuit voltage 430mV was achieved for combination of K and Na. Amongst the rest of alkali metals, Li looks the most promising dopant as far as optoelectronic properties are concerned.