An Extended Analytical Solution of the Non-Stationary Heat Conduction Problem in Multi-Track Thick-Walled Products during the Additive Manufacturing Process

An analytical model has been developed for calculating three-dimensional transient temperature fields arising in the direct deposition process to study the thermal behavior of multi-track walls with various configurations. The model allows the calculation of all characteristics of the temperature fields (thermal cycles, cooling rates, temperature gradients) in the wall during the direct deposition process at any time. The solution of the non-stationary heat conduction equation for a moving heat source is used to determine the temperature field in the deposited wall, taking into account heat transfer to the environment. The method considers the size of the wall and the substrate, the change in power from layer to layer, the change in the cladding speed, the interpass dwell time (pause time), and the heat source trajectory. Experiments on the deposition of multi-track block samples are carried out, as a result of which the values of the temperatures are obtained at fixed points. The proposed model makes it possible to reproduce temperature fields at various values of the technological process parameters. It is confirmed by comparisons with experimental thermocouple data. The relative difference in the interlayer temperature does not exceed 15%.

Direct deposition of lead sulfide nano-optoelectronic films on polymer substrate

Nanocrystals have exhibited unique optoelectronic properties and demonstrated a wide range of applications in light-emitting devices, semiconductor devices and solar cell devices. However, previous studies usually deposit nanocrystal films on traditional rigid substrates, limiting their applications in large-scale, direct-deposited flexible device fabrication processes, such as roll-to-roll printing process. Here, we report a direct deposition method for lead sulfide (PbS) nanocrystal films on flexible polymer substrates. By adding triethanolamine-coordinated Pb precursors to the reaction system to enhance the adhesion to the substrate and controlling the precursor ratios, we obtained high-quality flexible PbS films. The film is composed of octahedral PbS nanocrystals with preferred (111) orientation. The optical band gap of the nanocrystal films can be tuned from 1.32 eV to 1.60 eV by adjusting the ratio of the precursors, and an ideal band gap of 1.4 eV for single-junction solar cells was also obtained when Pb to S ratio reaches 1.4:1. More importantly, the flexible PbS films exhibit high charge carrier mobility of up to 25 cm2 V[Formula: see text] s[Formula: see text], which is comparable to that of PbS films grown on traditional rigid substrates (e.g. silicon wafers or glasses). To our knowledge, this mobility is also the highest for PbS fabricated directly on flexible substrates. Our study provides a new approach for the preparation of low-cost and roll-to-roll processable nanocrystal films for future flexible optoelectronic devices.