Donor:Acceptor Janus Nanoparticle‐Based Films as Photoactive Layers: Control of Assembly and Impact on Performance of Devices

Abstract

polymer solar cells (PSCs) can address the increasing global demand for renewable energy. [1,2] The deposition of the active layer in PSCs is generally processed with a halogenated solvent such as chloroform (CF), chlorobenzene (CB), and dichlorobenzene (DCB). [3][4][5] However, halogen atoms are detrimental to the human body and ecosystems; and therefore, substituting these toxic solvents is required for largearea fabrication and commercialization of PSCs. [6] The fabrication of semiconducting donor:acceptor (D:A) nanoparticles (NPs) dispersed in water offers a good solution to this issue [7,8] because it solves the problem of most organic photo-active donor/ acceptor materials having low solubility in green solvents. [9] On the other hand, the donor/acceptor phase morphology can be designed and well-controlled on the nanoscale. [10] Excitons dissociation can occur at the donor/acceptor (D/A) interface within the NPs, enabling them to extract electrons/holes efficiently. [11] Owing to their well-controlled internal nanostructures and environment-friendly processing, the aqueous D:A NP inks have been successfully applied to photocatalysis, [10][11][12][13] organic field-effect transistors, [14,15] photodetectors, [16] and photovoltaics. [17][18][19] However, the deposition of these aqueous NPs on substrates for applications remains a significant challenge. Generally, the most common approach is spin-coating. However, the concentration of D:A NP inks should be relatively high for this procedure (generally over 40 mg mL −1 ). [18] However, the donor and acceptor materials are often wasted during the coated process, especially for water-processable NPs. Furthermore, the concentration of surfactants should also be well-controlled to achieve the high quality of the spin-coated layers. Too high or low concentration leads to pinholes in the deposited layer. [20] However, the remaining surfactants would affect the performance of the devices. [20] In addition, the spin-coating approach cannot meet different substrates and large-scale manufacture. More importantly, the packing density of particles and surface morphology of the NP layer cannot be controlled through the spin-coating technique.Compared with spin-coating, air/water interfacial selfassembly is a simple, low-cost, and efficient approach to getting two-dimensional (2D) NP arrays. [21] Since Langmuir reported Water-processable organic semiconductor nanoparticles (NPs) are considered promising materials for the next-generation of optoelectronic applications due to their controlled size, internal structure, and environmentally friendly processing. Reasonably, the controllable assembly of donor:acceptor (D:A) NPs on large areas, quality, and packing density of deposited films, as well as layer morphology, will influence the effectiveness of charge transfer at an interface and the final performance of designed optoelectronic devices.This work represents an easy and effective approach for designing self-assembled monolayers of D:A NPs. In this self-assembly procedure, ...