Effective charge separation of inverted polymer solar cells using versatile MoS₂ nanosheets as an electron transport layer

Molybdenum disulfide (MoS₂) has been extensively used as a hole transport layer in many inverted polymer solar cell devices. However, its potential as an electron transport layer in a solar cell device has rarely been reported. In this paper, we demonstrate an iPSC with enhanced photovoltaic performance by the introduction of a MoS₂ nanosheet (NS) interlayer. Herein, MoS₂ NS thin films were uniformly deposited on a polyethylenimine ethoxylated polymer by an electrostatic interaction. The MoS₂ NS interlayer in the iPSC device plays important roles as a sub-photo sensitizer and an electron transport layer and provides effective charge separation for the enhancement of device performance. iPSCs with MoS₂ NSs based on bulk heterojunction active materials such as P3HT:PC₆₀BM, PTB7:PC₇₁BM and PTB7-Th:PC₇₁BM showed maximum power conversion efficiencies of 3.54%, 8.12%, and 9.08%, respectively, which were 27%, 11%, and 15% higher than those of the reference, respectively. Furthermore, the enhanced photovoltaic performance and electron transport mechanism of the iPSCs with the MoS₂ NSs were confirmed experimentally using finite-difference-time-domain modeling and time-correlated single photon counting (TCSPC) measurements. The computational simulation results showed that the light absorption of the iPSCs with the MoS₂ NS interlayer was slightly better than that of the iPSCs without the MoS₂ NS interlayer. The electron decay time of PTB7:PC₇₁BM with the MoS₂ NS interlayer at a wavelength of 700 nm was reduced to 60 ps from 100 ps of PTB7:PC₇₁BM without the MoS₂ NS interlayer. The efficient light absorption and electron transfer characteristics of MoS₂ NSs significantly improved the photovoltaic conversion performance of the iPSC devices.