Cu(In,Ga)Se 2 films doped with different contents of silver ions (Ag + ) were successfully prepared using nonvacuum spin coating followed by selenization at elevated temperatures. Increasing the Ag + ion content increased the lattice parameters of the chalcopyrite structure, and shifted the A1 mode in the Raman signals to low frequencies. The band gaps of the prepared (Ag, Cu)(In,Ga)Se 2 (ACIGS) films were considerably increased, thereby increasing the open-circuit voltage (V oc ) of the solar cells. As Ag + ion content increased, the microstructures of ACIGS films became densified because the formed (Cu,Ag) 2 In alloy phase with a low melting point facilitated liquid-phase sintering. The evaporation of selenium species was correspondingly suppressed in the films during selenization, thereby reducing the selenium vacancies. The improvement in the microstructures and the defects of ACIGS films increased short-circuit current (J sc ) and fill factor of the solar cells. The spectral response of the solar cells was also enhanced remarkably. This study demonstrated that incorporation of Ag + ions into Cu(In,Ga)Se 2 films substantially improved the efficiency of the solar cells.

The effects of selenization temperatures on the phase formation and the photovoltaic properties of silver-ion-doped Cu(In,Ga) Se 2 (ACIGS) films were investigated. Cu 2 -x Se phase coexisted with CuInSe 2 phase in the films as the selenization temperature was relatively low. Increasing the selenization temperatures promoted the formation of the chalcopyrite phase and increased the grain size. Upon increasing the selenization temperature to 600°C, single-phased ACIGS films with a grain size of 2.1-2.2 lm were successfully synthesized. The incorporation of Ag + and Ga 3+ ions into CuInSe 2 during the phase formation of ACIGS elevated the band gaps of the films, thereby improving the open-circuit voltage (V oc ) of the solar cells. The grain growth on raising the selenization temperatures also elevated the short-circuit current (J sc ) values owing to the suppression of the electron-hole recombination at grain boundaries. In the diode analysis, the facilitated phase formation suppressed the shunt path, decreasing the values of the diode factor (A), shunt conductance (G), and saturated current (J o ), thereby improving the cell performance. In this study, ACIGS solar cells with an efficiency of 7.21% prepared via the nonvacuum process were first demonstrated.

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