CuInSe2 thin film solar cells synthesised from electrodeposited binary selenide precursors

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The fabrication of a CuInSe2 thin film solar cell from an electrodeposited precursor stack consisting of indium selenide and copper selenide layers is demonstrated. A best conversion efficiency of 5.5% was achieved, a higher efficiency than previously reported in literature. The thesis focuses on three main parts:
(i) electrochemistry of indium selenide: The incorporation of indium in the deposit requires the presence of selenium species. The obtained film consists of both amorphous In2Se3 and elemental Se. The Se/In ratio depends on the applied potential, although the deposition is mass transport controlled limited by the selenium ion concentration. The potential controls the balance of reduction kinetics between the In2Se3 and elemental Se and both compete for the same intermediate selenium species.
(ii) phase reactions during annealing: The small interface area between the electrodeposited indium selenide and the copper selenide layer slows down the interdiffusion during the annealing process. Therefore the temperature required to react the precursor is higher than reported for similar stacks in literature. Copper selenide is retained at the surface for a longer time during the annealing process, where it undergoes the transitions CuSe2 => CuSe => Cu2Se.
(iii) loss mechanisms in the solar cell: The highest solar cell conversion efficiency was obtained from a stoichiometric precursor compromising the advantages and disadvantages of Cu-poor and Cu-rich growth. The Cu-poor grown absorber showed a reverse pn-junction at the backside due to an incomplete reaction of the stack. The efficiency of the Cu-rich grown solar cell was limited by high interface recombination.