Electrochemical Etching of CuInSe2

M. BERRUET; M. A. FRONTINI; M. VAZQUEZ

Niza, Francia

Congreso; 61st Meeting of the International Society of Electrochemistry.; 2010

CuInSe2 (CISe) is a p-type semiconductor, frequently used as the absorbing layer in photovoltaic solar cells. Its high absorption coefficient and a bandgap energy of 1.0 eV make it suitable for this application. However, binary phases such as copper and indium selenides can be formed during the synthesis and tend to be detrimental as regards the performance of the solar cell. This work aims at comparing the efficiency of electrochemical and conventional (KCN) etching, performed on CISe that has been deposited on top of conductive glass (TCO, SnO2:F) by two different techniques: electrodeposition (ED) and successive ionic layer adsorption and reaction (SILAR). The ED has been carried out potentiostatically at -0.8 V for 60 min, using a single bath. The electrolyte consisted of 0.4 mol/L sodium citrate containing 3 mmol/L CuCl2, 6mmol/L InCl3 and 5 mmol/L SeO2 [1]. The films were annealed at 400C for 20 min. The SILAR method employed a Na2SeSO3 anionic solution (pH 8.5) and a cationic solution containing a mixture of cupric and indium chloride aqueous solutions with chelating agents (pH=8) [2]. SILAR depositions were carried out at 80ºC performing 78 cycles of alternated immersions. The films were annealed in argon atmosphere at 400ºC for 1 hour. Electrochemical etching was carried out in acid (A) and basic (B) solutions: (A) potentiodynamically, from −0.5 to +0.5 VSCE at 10 mV/s in the 0.1mol/L H2SO4 solution (pH=1.2), and (B) potentiostatically at +0.4 V in 0.1 mol/L NaOH solution (pH=13.2) and later removing the formed oxides (or hydroxides) by immersion in acidic solutions (1 min in 0.1 M H2SO4 at −0.3 V) [3]. The efficiency of the etching treatments is compared by analyzing the deposits by X-ray diffraction (normal and glazing incidence) and EDX. The results show that samples of CISe obtained by different techniques present a differential response to the etching treatments. It is also clear that the chemical etching is a more superficial way of attack, while the electrochemical etching is able to affect the composition of the samples in greater depth. Also, while CN- etching mainly dissolves secondary phases containing Cu(II), the electrochemical procedure also affects In(III) compounds.