Effects of sputtering technique on quaternary sputtered Cu(In,Ga)Se2 films

While Cu(In,Ga)Se2 (CIGS) has established itself as the thin film photovoltaic material of choice with current record efficiencies in excess of 20%, current high-efficiency laboratory-scale fabrication techniques, such as multi-stage evaporation, are ill suited to mass production. Quaternary-sputtering is a promising alternative technique for CIGS deposition, where a single sputtering target made from CIGS itself in the desired stoichiometry is used as the sole deposition source. Devices made using this technique do not require any additional post deposition selenium treatment and have demonstrated peak efficiency in our laboratory in excess of 10%, showing the potential of quaternary sputtering. In an effort to reduce deposition times, we have fabricated films using pulsed DC sputtering, which substantially reduces the substrate time-at-temperature during absorber formation. DC-sputtered films are observed to have reduced surface roughness and different internal morphology from RF-sputtered films, but show increased crystallographic alignment along the (112) plane. DC-sputtered CIGS is thickness-limited to less than 600 nm due to excessive target damage and exhibits power conversion efficiencies of 5-6%.

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