Tunable Device Parameters of Polymer/CuInS<SUB>2</SUB> Solar Cells Depending on CuInS<SUB>2</SUB> Quantum Dot Size

This paper reports tunable device parameters of polymer/CuInS2 solar cells depending on CulnS2 quantum dot size, for the first time. The CuInS2 quantum dots (CuInS2-QDs) of tunable sizes displayed size-dependent band gaps, following by the size-dependent morphologies and optical properties in MEH-PPV-CuInS2 composites. Polymer/CulnS2 solar cells with poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) as polymer exhibited tunable device parameters depending on CuInS2-QDs size, resulting in a maximum power conversion efficiency of ca. 0.12% under the monochromic illumination at 470 nm in the device with the small-sized CuInS2-QDs. The origins for size-dependent performance in the solar cells are elucidated, which suggests that the higher short circuit current (Jsc) in the MEH-PPV/CuInS2 device with the small-sized QDs may due to the increased MEH-PPV/CuInS2 interface areas, while the higher open circuit voltage (Voc) may result from the higher energy difference between the conduction band position (Ec) of CuInS2-QDs and the highest occupied molecular orbital (HOMO) of the polymer. In particular, it is found that the device Voc is linearly dependent on the energy difference between Ec of CuInS2-QDs and HOMO of the polymer.