Solution-Processed in Situ Growth of CuInS2 Nanoparticle Films for Efficient Planar Heterojunction Solar Cells with a Dual Nature of Charge Generation

Abstract

A facile solution-processing method featuring the applications of a stable molecular precursor solution and the repetition of spin-coating and annealing for film growth is reported for the in situ growth of CuInS2 nanoparticle films on TiO2/CdS film to provide TiO2/CdS/CuInS2 ternary superstrate heterojunction films for efficient solar cells. The novel and stable planar solar cells are fabricated using Spiro-OMeTAD as hole transporting material (HTM) and achieved a peak power conversion efficiency of 6.31% under AM 1.5 illumination at the optimized CuInS2 thickness of 200 nm and annealing temperature of 270 °C for CuInS2 formation. The efficiency is the highest among the CuInS2-based planar solar cells derived from molecular precursor methods; in particular, adopting HTM results in the open-circuit voltage up to 0.78 V, much higher than that of the similar devices without HTM. Our results demonstrate a dual nature of excitonic and nonexcitonic charge generation mechanisms in such solar cells. A depletion-...