Influence of Cu off-stoichiometry on wide band gap CIGSe solar cells

H. Marko (1) , Ludovic Arzel (1) , Arouna Darga (2) , Nicolas Barreau (1) , Sébastien Noël , Denis Mencaraglia (2) , John Kessler (1)

1 IMN - Institut des Matériaux Jean Rouxel
2 LGEP - Laboratoire de génie électrique de Paris

The electric properties of solarcells based on co-evaporated Cu(In,Ga)Se2 (CIGSe) thin film show a good tolerance regarding the absorber Cu content (y = [Cu]/([In] + [Ga])) for standard Ga concentration, i.e. x = [Ga] / ([In] + [Ga]) ~ 0.3. In the present contribution, we show that this tolerance is lost when the gallium content is increased. Wide bandgap CIGSe samples (x ~ 0.55) with a variation in y from 0.97 to 0.84 have been grown. The efficiency of the cells decreases from 12.6% to 6.5% for y = 0.97 and 0.84 respectively. For the lowest y, the efficiency is harmed because of a low short-circuit current density (Jsc), an increased voltage dependency in the current collection, which affects the fill factor (FF), and a decrease of the open-circuit voltage (Voc). For y = 0.97 and 0.84 respectively, the decrease of the activation energy (Ea) from 1.36 to 1.24 eV indicates a shift of the area of the dominant recombination from the space charge region towards the interface. There seems to be evidence that reducing the Cu-content in the CIGSe thin film will cause a decrease in the width of the space charge region. Solarcells based on Cu-rich CIGSe (1.03 < y < 1.09) have also been fabricated and characterized. A strong deterioration of their electrical properties is observed despite the KCN etch of the segregated Cu2 − xSe binary phases at the surface, suggesting the presence of residual Cu2 − xSe precipitates within the layer.

H. Marko, Ludovic Arzel, Arouna Darga, Nicolas Barreau, Sébastien Noël, et al.. Influence of Cu off-stoichiometry on wide band gap CIGSe solar cells. Thin Solid Films, 2011, 519 (21), pp.7228-7231. ⟨10.1016/j.tsf.2010.12.174⟩. ⟨hal-00710734⟩