Spray-deposited CuInSe2 nanocrystal photovoltaics

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Abstract
Photovoltaic devices (PVs) were fabricated by spray-coating an ink of copper indium diselenide (CIS) nanocrystals as the light-absorbing layer. Without high-temperature post-deposition annealing, PVs were made on glass and plastic substrates with power conversion efficiencies of up to 1.9% and 1.1%, respectively, under AM1.5 illumination. The mild processing conditions also enabled fabrication of alternative device structures that are not compatible with conventional high-temperature PV processing, including substrate and superstrate designs, and devices with transparent back contacts of conducting indium tin oxide (ITO) and plastic substrates. Device performance is observed to be limited by poor charge extraction from the nanocrystal films, with the highest efficiencies being obtained from PVs with relatively thin absorber layers. To improve light absorption without sacrificing internal quantum efficiency, stacked PVs were fabricated, which exhibited improved short-circuit current and power conversion efficiency compared to stand-alone single junction devices.