Controlled electrodeposition of Cu–Ga from a deep eutectic solvent for low cost fabrication of CuGaSe2 thin film solar cells

Abstract

The electrochemical deposition of Ga and Cu-Ga alloys from the deep eutectic solvent choline chloride/urea (Reline) is investigated to prepare CuGaSe(2) (CGS) semiconductors for their use in thin film solar cells. Ga electrodeposition is difficult from aqueous solution due to its low standard potential and the interfering hydrogen evolution reaction (HER). Ionic liquid electrolytes offer a better thermal stability and larger potential window and thus eliminate the interference of solvent breakdown reactions during Ga deposition. We demonstrate that metallic Ga can be electrodeposited from Reline without HER interference with high plating efficiency on Mo and Cu electrodes. A new low cost synthetic route for the preparation of CuGaSe(2) absorber thin films is presented and involves the one-step electrodeposition of Cu-Ga precursors from Reline followed by thermal annealing. Rotating disk electrode (RDE) cyclic voltammetry (CV) is used in combination with viscosity measurements to determine the diffusion coefficients of gallium and copper ions in Reline. The composition of the codeposited Cu-Ga precursor layers can be controlled to form Cu/Ga thin films with precise stoichiometry, which is important for achieving good optoelectronic properties of the final CuGaSe(2) absorbers. The morphology, the chemical composition and the crystal structure of the deposited thin films are analysed by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). Annealing of the Cu-Ga films in a selenium atmosphere allowed the formation of high quality CuGaSe(2) absorber layers. Completed CGS solar cells achieved a 4.1% total area power conversion efficiency.

Insights into the Properties of Deep Eutectic Solvent Based on Reline for Ga-Controllable CIGS Solar Cell in One-Step Electrodeposition

“…[10][11][12][13] However, most of the works are carried out in aqueous solvents, in which hydrogen evolution reaction (HER) leads to low plating efficiencies and pinholes in the plating layer. 14,15 To avoid the occurrence of HER, researchers in recent years have turned to deep eutectic solvents (DES) as an electrolyte for electrochemical reactions due to their wide electrochemical window, high ionic conductivity, high solvation capacity, negligible vapor pressure and excellent stability. [16][17][18][19][20] Besides, DES, as a subclass of ionic liquids (ILs), is a green electrolyte for application in electroplating.…”

“…[16][17][18][19][20] Besides, DES, as a subclass of ionic liquids (ILs), is a green electrolyte for application in electroplating. [14][15][16][21][22][23] Reline, as one application of DES, is formed by choline chloride and urea at the ratio of 1:2. Harati et al fabricated successfully stoichiometric CIGS thin film by the one-pot electrodeposition in Reline as electrolyte.…”

A short review on the advancements in electroplating of CuInGaSe2 thin films

“…Table 1 [82]. Using DES such as reline, successful electrodeposition of CGSe has been reported [75]. Electrodeposition of Cu-Ga alloy using copper-gallium nitrate salts is also a good approach, where the inclusion of Ga takes place in the form of oxides/ hydroxides [63].…”

Low melting mixtures in organic synthesis – an alternative to ionic liquids?

“…3 Table 14 shows the conductivities observed in DESs which are comparable to ionic liquids; 44,45 DESs are therefore a highly investigated medium for electrochemical applications. [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63] Readers interested in electrodeposition from ILs and DESs will find a good review in ref. 64.…”