Lead sulphide (PbS) nanocrystals (NCs) are promising materials for low-cost, high-performance optoelectronic devices. So far, PbS NCs have to be first synthesized with long-alkyl chain organic surface ligands and then be ligand-exchanged with shorter ligands (two-steps) to enable charge transport. However, the initial synthesis of insulated PbS NCs show no necessity and the ligand-exchange process is tedious and extravagant. Herein, we have developed a direct one-step, scalable synthetic method for iodide capped PbS (PbS-I) NC inks. The estimated cost for PbS-I NC inks is decreased to less than 6 $·g−1, compared with 16 $·g−1 for conventional methods. Furthermore, based on these PbS-I NCs, photodetector devices show a high detectivity of 1.4 × 1011 Jones and solar cells show an air-stable power conversion efficiency (PCE) up to 10%. This scalable and low-cost direct preparation of high-quality PbS-I NC inks may pave a path for the future commercialization of NC based optoelectronics.

Current efforts on lead sulfide quantum dot (PbS QD) solar cells are mostly paid to the device architecture engineering and postsynthetic surface modification, while very rare work regarding the optimization of PbS synthesis is reported. Here, PbS QDs are successfully synthesized using PbO and PbAc · 3H O as the lead sources. QD solar cells based on PbAc-PbS have demonstrated a high power conversion efficiency (PCE) of 10.82% (and independently certificated values of 10.62%), which is significantly higher than the PCE of 9.39% for PbO-PbS QD based ones. For the first time, systematic investigations are carried out on the effect of lead precursor engineering on the device performance. It is revealed that acetate can act as an efficient capping ligands together with oleic acid, providing better surface coverage and replace some of the harmful hydroxyl (OH) ligands during the synthesis. Then the acetate on the surface can be exchanged by iodide and lead to desired passivation. This work demonstrates that the precursor engineering has great potential in performance improvement. It is also pointed out that the initial synthesis is an often neglected but critical stage and has abundant room for optimization to further improve the quality of the resultant QDs, leading to breakthrough efficiency.

PbS quantum-dot (QD) solar cells are promising candidates for low-cost solution-processed photovoltaics. However, the device fabrication usually requires ten more times film deposition and rinsing steps, which is not ideal for scalable manufacturing. Here, a greatly simplified deposition processing is demonstrated by replacing methanol with acetonitrile (ACN) as the rinsing solvent. It is discovered that ACN can effectively "cure" the film cracks generated from the volume loss during the solid-state ligand-exchange process, which enables the deposition of thick and dense films with much fewer deposition steps. Meanwhile, due to the aprotic nature of ACN, fewer trap states can be introduced during the rinsing process. As a result, with only three deposition steps for the active layer, a CPVT-certified 11.21% power conversion efficiency is obtained, which is the highest efficiency ever reported for PbS QD solar cells employing a solid-state ligand-exchange process. More importantly, the simple film-deposition processing provides an opportunity for the future application of QDs in low-cost printing of optoelectronic devices.

Colloidal quantum dot (CQD) solar cells processed from pre-exchanged lead sulfide (PbS) inks have received great attention in the development of scalable and stable photovoltaic devices. However, the current hole-transporting material (HTM) 1,2-ethanedithiol-treated PbS (PbS-EDT) CQDs have several drawbacks in terms of commercialization, including the need for oxidation and multilayer fabrication. Conjugated polymers are an alternative HTM with adjustable properties. Here we propose a series of conjugated polymers (PBDB-T, PBDB-T­(Si), PBDB-T­(S), PBDB-T­(F)) for PbS CQD solar cells as HTMs. Through polymer side-chain engineering, we optimize the model polymer PBDB-T to tune the energy levels, increase hole mobility, improve solid-state ordering, and increase free carrier density. CQD solar cells based on modified polymer PBDB-T­(F) exhibit a best power conversion efficiency (PCE) of 11.2%, which outperforms the devices based on conventional PbS-EDT HTM (10.6%) and is currently the highest PCE for PbS solar cells based on organic HTMs.

A multiple-passivation strategy by solution-phase ligand engineering in lead halide exchanged QDs ink is presented, which result in remarkably improved colloidal stability of QDs ink and enhanced device performance.