Biphasic Dip Coating for Versatile and Material-Efficient Nanoparticle Thin Films.

Colloidal quantum dot (cQD) thin films are central to solution-processed optoelectronics, yet scalable deposition methods that preserve device performance while improving material utilization remain limited. Here, we adapt a biphasic meniscus dip coating strategy that enables controlled deposition of cQD films while substantially reducing the volume of active nanocrystal solution required. In this approach, a thin cQD layer is supported by an immiscible underlayer, such that film formation occurs exclusively at the liquid-air interface of the active phase. Using this geometry, we fabricate PbS quantum dot photodetectors with responsivities up to ∼1000 mA/W at 1200 nm, comparable to conventional spin-coated devices. Relative to spin coating, the biphasic configuration reduces active solution consumption by up to 20-fold while maintaining film quality and reproducible device performance. A mass-volume cost analysis shows that the reduced active reservoir shifts the economic viability of dip coating into thickness and throughput regimes more relevant to practical device fabrication. We further extend the method to CsPbBr3 nanocrystals and curved substrates, highlighting its generality across material systems and geometries. Together, these results establish biphasic dip coating as a material-efficient and device-compatible manufacturing strategy for solution-processed optoelectronics.