PhD Thesis Colloquium: Mr. Mohammed Hadhi PP (12/01/26)
Thesis title:
Directed assembly of nanomaterials towards scalable and reliable solution-processed electronics
Faculty advisor(s):
Prof. Subho Dasgupta
When?
12th January, 2026 (Monday), 4:00 PM (India Standard Time)
Where
KPA Auditorium, Department of Materials Engineering
Abstract:
Solution-processed electronics represent a transformative platform for realizing large-area, flexible, low-cost, and sustainable electronic systems and solutions with potential applications spanning from wearable devices, disposable sensors, bioelectronics, Internet of Things (IoT) to neuromorphic computing. Despite over two decades of intensive research, the commercial viability of solution-processed thin-film transistors (TFTs) remains constrained by numerous fundamental challenges, including device-to-device variability, scalability limitations, operational reliability, fabrication economics, and insufficient application-level validation. This dissertation addresses these critical bottlenecks through the development and comprehensive investigation of electric-field-assisted directed nanomaterial assembly for TFT fabrication and their applications in various disciplines. The primary objective of this research is to advance the state-of-the-art in solution-processed electronics by establishing a universal, material-agnostic, and substrate-independent semiconductor assembly framework that concurrently enhances the variability, scalability, performance, sustainability and cost-effectiveness of the TFTs. This work demonstrates that precise control with electrokinetic assembly enables deterministic placement and alignment of semiconducting nanomaterials, thereby overcoming the inherent stochastic limitations of conventional solution-processing techniques. At first, device variability by a combination of two solution processing techniques has been examined through the controlled dielectrophoretic assembly of semiconducting nanomaterials. By optimizing assembly parameters, deterministic nanomaterial placement with nearly 100% positioning probability could be achieved, overcoming the stochastic nature of conventional solution processing techniques. Indium oxide nanowire devices thus fabricated on rough paper substrates using the directed assembly approach exhibit 3.5× lower device-to-device variability compared to inkjet-printed counterparts, while maintaining high electrical performance with an On-Off ratio of 107, mobility of 42 cm2 V-1 s-1, and mechanical robustness down to a bending radius of 1.5 mm.
Next, scalability and performance have further been demonstrated using high-mobility two-dimensional semiconductors. Dielectrophoretic forces enable single-flake assembly within transistor channels, eliminating inter-flake junction resistance and enabling near-intrinsic charge transport. Wafer-scale fabrication of 16,000 transistors on a 3-inch wafer has been achieved within 8 minutes, with yields exceeding 97%. The resulting devices exhibit excellent operational stability, high current densities up to 200 µA µm-1, mobility values averaging at 51 cm2 V-1 s-1, and overall electrical performance comparable to vapor-deposited counterparts. Vertical nanochannel transistors further achieved an On-current density as high as 1 mA µm-1. Further, to address fabrication cost and energy consumption, a self-powered nanomaterial assembly approach is introduced using a triboelectric nanogenerator fabricated from low-cost disposable shoe cover. Powered solely by human motion, this system generates the electric fields required for nanomaterial assembly without external power sources. The feasibility of this approach is demonstrated through the fabrication of TFTs, diodes, and volatile organic compound sensors, establishing a pathway toward energy-autonomous and sustainable electronics manufacturing.
Finally, the versatility of the fabricated devices has been demonstrated across multiple application domains. Paper-based TFTs exploit slow ionic dynamics arising from electrolyte–cellulose interactions to emulate synaptic behaviour, enabling functions, such as speech recognition derived from eye-movement signals. In parallel, single-flake TFTs enable high-frequency digital operation, achieving voltage gains up to 9.5, rail-to-rail switching at 2 kHz, and the realization of all fundamental logic gates. Overall, this thesis establishes electric-field-assisted directed assembly as a comprehensive and scalable strategy to overcome some of the longstanding limitations in solution-processed electronics and paves way towards a strong possibility for industrial adoption and commercial success.