Solution-processed CuSCN/WS2 hole transport layer for enhancing efficiency of organic solar cells

Two-dimensional (2D) transition metal dichalcogenides (TMDs) materials have been applied in organic solar cells (OSCs), which possess excellent light transmittance, good charge carrier selectivity and high mobility. Herein, high quality 2D material of tungsten disulfide (WS2) nanosheets is synthesized by liquid exfoliation method, which is used to form a double-layer hole transport layer with soluble copper(I) thiocyanate (CuSCN). The introduction of WS2 nanosheets smooth the surface of CuSCN hole transport layers (HTL) and modify the interface between CuSCN HTL and light absorber. The cells using double-layer CuSCN/WS2 as HTL exhibit higher light photon utilization, weaker recombination loss compared to the reference cell with pristine CuSCN HTL. More importantly, it has been proved that the WS2 nanosheets act as intermedium between light absorbers and CuSCN, which contribute to efficient hole extraction process. As a result, a champion power conversion efficiency (PCE) of 9.00% is obtained in PTB7-Th:PC71BM light absorber based cell using CuSCN/WS2 as HTL, which is > 16% higher than the PCE of 7.75% achieved in reference cell with pristine CuSCN HTL. This result proves that 2D TMDs materials are promising candidates as charge selectivity for highly efficient solar cells.