Abstract
The two-step process including the deposition of the metal precursors followed by heating the metal precursors in a vacuum environment of Se overpressure was employed for the preparation of Cu(In,Ga)Se2 (CIGS) films. The CIGS films selenized at the relatively high Se flow rate of 25 Å/s exhibited improved surface morphologies. The correlations among the two-step process parameters, film properties, and cell performance were studied. With the given selenization conditions, the efficiency of 12.5% for the fabricated CIGS solar cells was achieved. The features of co-evaporation processes including the single-stage, bi-layer, and three-stage process were discussed. The characteristics of the co-evaporated CIGS solar cells were presented. Not only the surface morphologies but also the grading bandgap structures were crucial to the improvement of the open-circuit voltage of the CIGS solar cells. Efficiencies of over 17% for the co-evaporated CIGS solar cells have been achieved. Furthermore, the critical factors and the mechanisms governing the performance of the CIGS solar cells were addressed.
Highlights
The CIGS-based films are commonly prepared by the two-step or co-evaporation processes, where the two-step process is called the sulfurization after selenization (SAS) process [1].The thin-film CIGS solar cells have reached efficiencies of over 20%, where the CIGS films were prepared by the co-evaporation method [2,3,4,5]
The CIGS films were prepared by the two-step process which consisted of the preparation of the metal precursors followed by heating the metal precursors in an environment containing an overpressure of Se vapor
Characteristics of a CIGS solar cell prepared by the two-step process, (c) the derivative of dJ/dV for the determination of the shunt characteristics, (d) the derivative of dV/dJ in forward bias with fit used to determine the series resistance and the diode ideality factor, and (e) ln(J + JSC − GV) with fit used to determine the reverse saturation current density and the diode ideality factor. (Eff. and Eff.active denote the total-area efficiency and active-area efficiency, respectively)
Summary
The CIGS-based films are commonly prepared by the two-step or co-evaporation processes, where the two-step process is called the sulfurization after selenization (SAS) process [1]. The two-step and co-evaporation processes have been widely employed for mass production of the large-scale CIGS-based modules [11,12]. Another favorite approach in CIGS industry is the rapid thermal process (RTP), in which a thin Se layer is first capped on the top of metal precursors, CuInGa compounds, and the diluted H2 S gas is supplied to simultaneously sulfurize and selenize the precursors to form the Cu(In,Ga)(S,Se) (CIGSS) films in an RTP furnace [13]. The co-evaporation process is a superior approach for the fabrication of CIGS-based solar cells with respect to device performance, high efficiencies can be achieved with the two-step process. The correlations of the deposition process, film properties, and cell performance were investigated
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