Efficient PbS quantum dots tandem solar cells through compatible interconnection layer

Abstract

Lead sulfide quantum dots (PbS QDs) hold unique characteristics, including bandgap tunability, solution-processability etc., which make them highly applicable in tandem solar cells (TSCs). In all QD TSCs, its efficiency lags much behind to their single junction counterparts due to the deficient interconnection layer (ICL) and defective subcells. To improve TSCs performance, we developed three kinds of ICL structures based on 1.34 and 0.96 eV PbS QDs subcells. The control, 1,2-ethanedithiol capped PbS QDs (PbS-EDT)/Au/tin dioxide (SnO2)/zinc oxide (ZnO), utilized SnO2 layer to obtain high surface compactness. However, its energy level mismatch causes incomplete recombination. Bypassing it, the second ICL (PbS-EDT/Au/ZnO) removed SnO2 and boosted the power conversion efficiency (PCE) from 5.75% to 8.69%. In the third ICL (PbS-EDT/poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)/Au/ZnO), a thin layer of PTAA can effectively fill fissures on the surface of PbS-EDT and also protect the front cells from solvent penetration. This TSC obtained a PCE of 9.49% with an open circuit voltage of 0.91 V, a short circuit current density of 15.47 mA/cm2, and a fill factor of 67.7%. To the best of our knowledge, this was the highest PCE achieved by all PbS QD TSCs reported to date. These TSCs maintained stable performance for a long working time under ambient conditions.