The effect of water on colloidal quantum dot solar cells

Abstract

Almost all surfaces sensitive to the ambient environment are covered by water, whereas the impacts of water on surface-dominated colloidal quantum dot (CQD) semiconductor electronics have rarely been explored. Here, strongly hydrogen-bonded water on hydroxylated lead sulfide (PbS) CQD is identified. The water could pilot the thermally induced evolution of surface chemical environment, which significantly influences the nanostructures, carrier dynamics, and trap behaviors in CQD solar cells. The aggravation of surface hydroxylation and water adsorption triggers epitaxial CQD fusion during device fabrication under humid ambient, giving rise to the inter-band traps and deficiency in solar cells. To address this problem, meniscus-guided-coating technique is introduced to achieve dense-packed CQD solids and extrude ambient water, improving device performance and thermal stability. Our works not only elucidate the water involved PbS CQD surface chemistry, but may also achieve a comprehensive understanding of the impact of ambient water on CQD based electronics.

Fundamental Processes and Practical Considerations of Lead Chalcogenide Mesocrystals Formed via Self-Assembly and Directed Attachment of Nanocrystals at a Fluid Interface

“…Zherebetskyy et al showed that dissociated water molecules can hydroxylate the PbS NC surface . More recently, Shi et al examined the detailed impact of surface hydroxylation on PbS NC fusion, electronic structure, and device performance . In all cases, it is important to perform the purification process in a short period of time to minimize exposure to air or preferably perform the purification process in an inert atmosphere if possible.…”

“…86 More recently, Shi et al examined the detailed impact of surface hydroxylation on PbS NC fusion, electronic structure, and device performance. 87 In all cases, it is important to perform the purification process in a short period of time to minimize exposure to air or preferably perform the purification process in an inert atmosphere if possible. For the most reproducible results, ligand coverage can be determined qualitatively using FTIR 75,88 and quantitatively via 1 H-NMR; 51,85,89,90 typical ligand coverages are in the range of 1−5 ligands/nm 2 .…”

Unprecedentedly Large Photocurrents in Colloidal PbS Quantum-Dot Solar Cells Enabled by Atomic Layer Deposition of Zinc Oxide Electron Buffer Layer

“…7 Imbalanced size distribution would cause charge trapping at larger dots with lower band gap. 8 Similar problems could occur when nonpassivated surface defects of QDs function as trapping sites. 9,10 Correspondingly, enormous efforts were given to develop passivation skills as well as to improve the size uniformity.…”

“…Second, the charge transport within QD films is predominantly determined by the size uniformity of the QDs as well as their surface property . Imbalanced size distribution would cause charge trapping at larger dots with lower band gap . Similar problems could occur when nonpassivated surface defects of QDs function as trapping sites. , Correspondingly, enormous efforts were given to develop passivation skills as well as to improve the size uniformity. , Third, lack of back surface field in the QD layer may deteriorate carrier extraction from the backside.…”

Guanidinium-Pseudohalide Perovskite Interfaces Enable Surface Reconstruction of Colloidal Quantum Dots for Efficient and Stable Photovoltaics

“…In the former, the successful demonstration of solution-phase ligand exchange has enabled highly passivated CQDs. However, it has recently been found that oxidative species in ambient conditions, such as oxygen and humidity, result in oxidation of the CQD surface, causing detrimental effects on the device. − In the latter case, chemical treatments have improved electronic coupling over the CQDs by connecting them, but this approach conversely compromises the surface passivation, such as merging of CQDs …”