Enhancing the Power Output of InSe-Based Screen-Printed Flexible Thermoelectric Generators through a Bi-Te-Co-Doping Strategy.

The advancement of flexible thermoelectric generators (FTEGs) is hindered by the brittleness, rigidity, and complex processing of conventional materials, as well as challenges in achieving both mechanical durability and efficient charge transport. Although single-element doping, alloying, and nanostructuring have been explored to enhance thermoelectric performance, they often require complex synthesis or cause trade-offs between electrical and thermal transport. Here, we show that Bi/Te codoping in indium selenide (InSe) provides a more effective approach by simultaneously optimizing carrier concentration and introducing phonon scattering centers, thereby achieving balanced improvements in the Seebeck coefficient, electrical conductivity, and thermal conductivity. Bi/Te codoped InSe powders were synthesized via a conventional solid-state reaction method, and flexible FTEGs were subsequently fabricated using a facile and scalable screen-printing technique, providing a cost-effective and industrially viable alternative. Structural analysis confirms the formation of phase-pure hexagonal InSe, with enhanced crystallinity achieved at an optimal 4% Bi doping level. Hall effect measurements reveal that codoping significantly improves electrical properties, resulting in a high Seebeck coefficient (-452 μV/K), increased voltage output (47 mV), and superior power output (∼0.14 nW at ΔT = 116 °C) for the In0.96Bi0.04Se0.97Te0.03 composition, representing a 6-fold increase in power output compared to pristine InSe. Moreover, the fabricated devices exhibit exceptional flexibility and mechanical reliability, maintaining electrical performance with ∼5% resistance variation under bending and 500 mechanical cycles. This work not only demonstrates a high-performing n-type InSe-based flexible thermoelectric material but also establishes a practical route toward scalable, wearable energy-harvesting devices.