The field of optoelectronics has seen transformative advances with the emergence of twistronics, a discipline focused on angle-engineered heterostructures. By precisely controlling the rotational alignment between stacked two-dimensional materials, researchers can manipulate electronic and optical properties with unprecedented precision. This capability has opened new avenues for designing tunable photodiodes, light-emitting devices, and sensors with tailored performance metrics. Central to these developments are moiré excitons, which arise from the periodic potential modulation in twisted heterostructures, enabling fine control over light-matter interactions.

Moiré excitons form when two atomically thin semiconductors, such as transition metal dichalcogenides (TMDCs), are stacked with a slight rotational misalignment. The resulting moiré pattern creates a superlattice that localizes excitons—bound electron-hole pairs—at specific energy levels determined by the twist angle. For instance, in a heterobilayer of MoSe2-WSe2 twisted at 5 degrees, moiré excitons exhibit sharp photoluminescence peaks with energies shifted by approximately 30 meV compared to the untwisted case. This energy tuning directly influences the absorption and emission spectra, making twistronics a powerful tool for optoelectronic design.

One of the most promising applications of twistronics is in tunable photodiodes. By adjusting the twist angle between TMDC layers, the spectral response of these devices can be precisely engineered. A study involving a MoS2-WS2 heterostructure demonstrated that varying the twist angle from 0 to 60 degrees resulted in a photoresponse shift across a range of 1.5 to 2.0 eV. This tunability allows the same material system to target different wavelengths without requiring chemical composition changes. Additionally, the quantum efficiency of such devices can exceed 20% at optimal twist angles, rivaling conventional photodiodes while offering superior flexibility in design.

The photoresponse of twisted heterostructures is not limited to simple absorption shifts. The moiré potential also enhances exciton lifetimes by suppressing non-radiative recombination pathways. In twisted bilayer MoTe2, exciton lifetimes have been measured at up to 10 nanoseconds, significantly longer than the sub-nanosecond lifetimes observed in monolayers. This extended lifetime improves charge collection efficiency in photodetectors, leading to higher responsivity. Experimental data from a 15-degree-twisted MoS2-MoSe2 device showed a responsivity of 0.5 A/W under 650 nm illumination, outperforming many traditional semiconductor photodiodes in this spectral range.

Beyond photodiodes, twistronics enables novel light-emitting devices with adjustable emission wavelengths. A notable example is the development of twist-angle-dependent LEDs using WSe2-MoS2 heterostructures. At a twist angle of 10 degrees, these devices emit light at 1.65 eV, while a 20-degree twist shifts the emission to 1.55 eV. The ability to modulate emission energy purely through structural alignment eliminates the need for alloying or doping, simplifying fabrication and reducing material constraints. Furthermore, the external quantum efficiency of these LEDs reaches 8% at room temperature, demonstrating their practical viability.

The impact of twistronics extends to photovoltaic applications, where moiré excitons can enhance light absorption and carrier extraction. In a study involving twisted graphene-TMDC heterostructures, the moiré superlattice was shown to increase photon absorption by 15% compared to random stacking. This enhancement arises from the additional electronic states introduced by the moiré potential, which create more pathways for exciton generation. When integrated into solar cells, such structures have achieved power conversion efficiencies of 12%, highlighting their potential for next-generation photovoltaics.

Challenges remain in scaling twistronics for industrial applications. Precise angle control at wafer scales requires advanced fabrication techniques, such as transfer-printing with sub-degree accuracy. Thermal stability is another concern, as small temperature variations can alter twist angles and degrade device performance. However, recent progress in encapsulation methods has improved thermal robustness, with some twisted heterostructures maintaining their optoelectronic properties up to 200 degrees Celsius.

The future of twistronics in optoelectronics lies in expanding the library of materials and exploring more complex heterostructures. For example, combining TMDCs with graphene or hexagonal boron nitride could unlock additional functionalities, such as ultrafast charge transfer or enhanced light extraction. Theoretical models predict that trilayer twisted systems could exhibit even richer excitonic behavior, with potential applications in quantum light sources.

In summary, twistronics represents a paradigm shift in optoelectronic engineering, offering unparalleled control over device performance through angular design. Moiré excitons serve as the cornerstone of this approach, enabling tailored photoresponse in tunable photodiodes, LEDs, and solar cells. While technical hurdles persist, the rapid progress in fabrication and characterization techniques suggests that angle-engineered heterostructures will play a central role in the next generation of optoelectronic technologies. The ability to fine-tune optical properties without altering chemical composition provides a versatile platform for innovation, paving the way for devices with customized performance metrics across a broad spectral range.