Copper thiocyanate (CuSCN): an efficient solution-processable hole transporting layer in organic solar cells†
Here, we report copper(I)thiocyanate (CuSCN) as an efficient and solution-processable hole transport layer (HTL) in bulk heterojunction solar cells. Three different combinations of the most studied active layers of P3HT:PC61BM, PCDTBT:PC71BM and PTB7:PC71BM were used for photovoltaic device fabrication with the simplest device structure of ITO/CuSCN/active layer/Al. The use of CuSCN as an HTL has improved light absorption within the active layer and thereby leads to up to 5.94% and 4.60% power conversion efficiencies (PCEs) for the active layers of PCDTBT:PC71BM and PTB7:PC71BM, respectively. These results are slightly better when compared to the devices fabricated using thermal deposition of MoO3 and solution processed deposition of PEDOT:PSS as an HTL under similar conditions. We have observed that the annealing temperature for HTLs in organic solar cells has a significant effect on the PCE, specifically the fill factor (FF) and short-circuit current (Jsc). In the present work, the resulting HTLs were characterized using UV-vis-NIR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) for better understanding. Finally, we have provided a further example of solution-processable CuSCN as an efficient HTL in organic solar cells, in general.