Kesterite Inorganic-Organic Heterojunction for Solution Processable Solar Cells

New synthesis of solution processable kesterite and kesterite-phenoxazine nanopowders were presented. The direct band-gap semiconductor Cu₂ZnSnS₄ has attracted the attention of many due to its large absorption coefficient (α > 10⁴ cm^-1) and (optical) band-gap energy close to the optimal value for solar light conversion (1.4-1.6 eV). The presence of a kesterite nanocrystal structure has been investigated and confirmed by (HR)TEM, X-ray powder diffraction, EDX and EXAFS measurements. Low-temperature photoluminescence (PL) measurements indicate the absence of PL in the Cu₂ZnSnS₄ nanocrystals. Electrochemical studies helped to prove that an inorganic-organic heterojunction of nanokesterite-phenoxazine was obtained. Device studies showed a two fold improvement in efficiency upon addition of a kesterite or phenoxazines-kesterite layer.