Improving PbS Colloidal Quantum Dot Solar Cell Performance via Solution-Phase Engineering

Lead Sulfide (PbS) colloidal quantum dots (CQDs) are promising materials for flexible and wearable photovoltaic devices and technologies due to their low cost, solution processibility and bandgap tunability with quantum dot size. However, PbS CQD solar cells have limitations on performance efficiency due to charge transport losses in the CQD layers and hole transport layer (HTL). This study pursues two promising techniques in parallel to address these challenges. Solution-phase annealing of the absorbing PbS-PbX2 (X = Br, I) layer can reduce charge transport losses by removing oleic acid and parasitic hydroxyl ligands. Additionally, optoelectronic simulations are used to show that HTL performance can be improved by the addition of a 2D transition metal dichalcogenide (TMD) layer to the PbS CQD-based HTL. We use solution-phase exfoliation to produce and incorporate 2D WSe2 nanoflakes into the HTL. We report a power conversion efficiency (PCE) increase of up to 3.4% for the solution-phase-annealed devices and up to 1 % for the 2D WSe2 HTL augmented devices. A combination of these two techniques should result in high-performing PbS CQD solar cells, paving the way for further advancements in flexible photovoltaics.