Incorporating CuInS2 quantum dots into polymer/oxide-nanoarray system for efficient hybrid solar cells

Abstract

This paper describes for the first time a feasible strategy to prepare efficient hybrid solar cells that combine ideal bulk-heterojunction architecture and wide spectral response in ternary photoactive layer. CuInS2 quantum dots (CuInS2-QDs) with different sizes were controllably synthesized by the solvothermal method; MEH-PPV–CuInS2 hybrids for harvesting photons in a broad spectral range up to 900nm were prepared by blending CuInS2-QDs with poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV), in which CuInS2-QDs aggregate into continuous and highly condensed interpenetrating nanochannels with the presence of effective MEH-PPV/CuInS2 interface for the energy transfer from MEH-PPV to CuInS2-QDs. Solar cells were fabricated by using the MEH-PPV–CuInS2 hybrids as light-harvester and vertically aligned TiO2 nanorod array (TiO2-NA) as a straightforward electron transporter, producing MEH-PPV–CuInS2/TiO2-NA devices with a ternary photoactive layer, and a power conversion efficiency of 1.60% was achieved under AM1.5 illumination. Compared to MEH-PPV/TiO2-NA binary solar cells, MEH-PPV–CuInS2/TiO2-NA ternary devices exhibit a much larger photocurrent and thereby efficiency. It is demonstrated that, in the ternary solar cells, photocurrent generation correlates dominantly with the light absorption property of MEH-PPV–CuInS2 hybrids, while open-circuit voltage is still mainly determined by the energy difference between the conduction band edge of TiO2 nanorods and the highest occupied molecular orbital level of the polymer. Based on the morphology and band alignments in the ternary system, the contributions of CuInS2-QDs to device performance and the related charge generation and transport processes are described.