Preparation of In-rich CuInSe2 photovoltaic films by varying the concentration of sorbitol as the third complexing agent

摘要

Ternary or quartenary chalcopyrite compounds, such as CuInSe2, Cu(In,Ga)Se2, CuIn(Se,S)_2 and CuGaSe2, are excellent materials in inorganic thin film solar cells due to their high absorption coefficients (～10~5cm~(-1)). These films have been prepared by coevaporation or sputtering in a vacuum chamber. Alternative non-vacuum fabricating processes have attracted considerable attention from the point of processing cost. Electrodeposition is an alternative to prepare a dense, smooth, and continuous film of CuInSe2. The CuInSe2 can be further crystallized and its grains are grown through a high-temperature annealing step. For a high-efficiency solar cell, the film needs to be In-rich. Namely, the atomic ratio of [Gu]/[In] needs to be as low as 0.85～0.95. The In-rich films can be prepared by using high-concentration In precursors or by using complexing agents in the electrodeposition. KCN treatment of the annealed CuInSe2 film also reduces the [Cu]/[In] ratio by etching secondary phases of Cu_xSe concentrated around the film surface. However, excessive KCN etching can produce pinholes, crevices or dents, which cause shunt paths in the device. In order to prepare an In-rich film along with the alleviated KCN etching, large amount of In needs to be deposited during electrodeposition. With the known binary complexing agents, sulfamic acid and potassium biphthalate, there is a limit to increase the In content in the CuInSe2 film. However, we could prepare a continuous and smooth In-rich film by adapting sorbitol as the third complexing agent. This study exhibits the adjustment of the complexing agents and the effect of sorbitol for preparing a device-quality CuInSe2 film.