Atomic layer deposition of zinc oxide and indium sulfide layers for Cu(In,Ga)Se2 thin-film solar cells

Atomic layer deposition (ALD) of ZnO and indium sulfide layers has been investigated. In situ monitoring at the monolayer level has been made by using quartz crystal microgravimetry (QCM), with a special focus on extrinsic doping of ZnO with Al. Cu(In,Ga)Se2/In2S3 (ALE)/ZnO (ALE) cells present efficiencies up to 13.5%. Indium sulfide layers used in these cells are characterized by a high band-gap value (up to 3.3 eV). They possess an amorphous like structure and a composition close to In2S3 as determined by Rutherford Back Scattering measurements. Lowering of the band-gap and crystallization take place under annealing, indicating that the high band-gap value of ALE indium sulfide layer is most likely related to structural effects.