Comparative study of the influence of LiF, NaF, and KF on the performance of polymer bulk heterojunction solar cells

Abstract
Based on the well-known beneficial effect of a thin LiF layer underneath Al contacts for organic solar cells, a comparative study of interlayers made from the alkaline fluorides LiF, NaF, and KF is presented for polymer bulk heterojunctionsolar cells. The overall suitability of these materials and the underlying mechanisms are discussed. While an improvement in cell efficiency up to a factor of 2 can be reached with all three fluorides, the necessary thickness of the interlayer for maximum improvement is smallest for NaF and largest for LiF, suggesting the alternative use of NaF instead of LiF.