Philip Jackson, Dimitrios Hariskos, Roland Wuerz, Wiltraud Wischmann and Michael Powalla
Thin films of Cu(In,Ga)Se2 (CIGS) due to their exceptionally good light absorption properties can get by with a very thin photo-active layer of only 2–3 μm whilst still catching the sun's energy. With such a sparing use of materials as compared to traditional technologies based on silicon, thin-film solar cells promise a major production cost reduction. Up to now, however, thin-film photovoltaics never could reach the same conversion efficiency level as the silicon based devices. Now CIGS, with a new record efficiency of 20.8% on the laboratory scale (see the Letter by Philip Jackson et al., pp. 219–222), for the first time outshines a major silicon competitor, multicrystalline silicon (20.4%). The key to this break-through was the application of a new doping technique. Doping in CIGS is significantly more complex than in silicon solar cells due to its multinary structure, the various intrinsic crystal defects and the diffusion of various contaminants from the glass substrate. The improvement in controlling this complex doping process has led to a remarkable increase in device performance. Due to the more complex physical and chemical environment of CIGS and the resulting multifaceted interactions, the new doping technique also enables production of CIGS solar cells with higher band gaps and higher open-circuit voltages.