Periodic Reporting for period 1 - MaDLED (Mastering Electronic Doping in Tin-Halide Perovskites to Develop Near Infrared Light Emitting Diodes)
Periodo di rendicontazione: 2024-01-01 al 2025-12-31
Near-infrared light (NIR, roughly 800–1000 nm) is widely used in everyday technologies, from secure sensing and night-vision style detection to biomedical imaging and optical communications. Today’s mainstream NIR emitters often rely on high-temperature vacuum epitaxy of inorganic semiconductors, which can be costly and difficult to scale to large areas or flexible formats. Solution-processed metal-halide perovskites offer an attractive alternative because they can be deposited at low temperature from inks, while keeping excellent optoelectronic properties.
However, pushing efficient emissions beyond 800 nm remain challenging. Tin-halide perovskites (THPs) are among the most promising candidates because their emission wavelength can be tuned from deep red to NIR region (670 – 1000 nm), and they enable lead-free device concepts that align with Europe’s ambition for greener electronics.
The central obstacle is that THPs tend to be strongly self p-doped due to the tin redox chemistry and defects. Excessive p-doping and deep trap states promote non-radiative losses (trap-assisted recombination and Auger recombination), lowering light-emission efficiency of LEDs.
The project’s overall objective was therefore to master and modulate self p-doping and defect chemistry in tin-halide perovskites, and to translate that understanding into improved NIR-LED performance and stability. This pathway to impact links fundamental photophysics (how charges recombine and where they are lost) to practical materials design and device engineering, targeting scalable NIR light sources for future sensing, health, and communication technologies.
However, pushing efficient emissions beyond 800 nm remain challenging. Tin-halide perovskites (THPs) are among the most promising candidates because their emission wavelength can be tuned from deep red to NIR region (670 – 1000 nm), and they enable lead-free device concepts that align with Europe’s ambition for greener electronics.
The central obstacle is that THPs tend to be strongly self p-doped due to the tin redox chemistry and defects. Excessive p-doping and deep trap states promote non-radiative losses (trap-assisted recombination and Auger recombination), lowering light-emission efficiency of LEDs.
The project’s overall objective was therefore to master and modulate self p-doping and defect chemistry in tin-halide perovskites, and to translate that understanding into improved NIR-LED performance and stability. This pathway to impact links fundamental photophysics (how charges recombine and where they are lost) to practical materials design and device engineering, targeting scalable NIR light sources for future sensing, health, and communication technologies.
The project combined thin-film engineering, advanced spectroscopy and microscopy, and LED device prototyping to address two tightly connected questions: (i) how to suppress tin oxidation and harmful defects while keeping beneficial levels of doping, and (ii) how to ensure efficient charge injection and radiative recombination in NIR-LED stacks. The work employed complementary characterization tools (e.g. photoluminescence mapping and quantum-yield analysis, transient spectroscopy to follow carrier dynamics, and structural probes to track crystallization and phase formation) to connect processing conditions with optoelectronic quality.
A key outcome was the demonstration of a molecularly engineered “self-encapsulated” tin-iodide perovskite thin film. By introducing a rationally designed organic molecule into the precursor solution, the film formation was slowed and guided in a way that (a) suppressed rapid degradation in air by mitigating Sn²⁺ oxidation; (b)reduced trap-related losses; and (c) enabled partial control over the p-doping level (without forcing the material to become fully intrinsic).
This self-encapsulation concept delivered clear, measurable improvements. This approach increased the photoluminescence quantum yield, with a reported peak of ~45% under relevant excitation conditions, indicating substantially reduced non-radiative losses. Meanwhile, the perovskite film retained ~60% of its initial photoluminescence after 100 minutes in ambient air (without external encapsulation), whereas reference films degraded immediately. Building on these higher-quality films, the project fabricated NIR-LEDs that achieved a record peak external quantum efficiency (EQE) of 12.4%. Notably, the devices demonstrated measurable functionality in ambient air without external encapsulation (even though long-duration air operation remains a challenge for the broader field).
A key outcome was the demonstration of a molecularly engineered “self-encapsulated” tin-iodide perovskite thin film. By introducing a rationally designed organic molecule into the precursor solution, the film formation was slowed and guided in a way that (a) suppressed rapid degradation in air by mitigating Sn²⁺ oxidation; (b)reduced trap-related losses; and (c) enabled partial control over the p-doping level (without forcing the material to become fully intrinsic).
This self-encapsulation concept delivered clear, measurable improvements. This approach increased the photoluminescence quantum yield, with a reported peak of ~45% under relevant excitation conditions, indicating substantially reduced non-radiative losses. Meanwhile, the perovskite film retained ~60% of its initial photoluminescence after 100 minutes in ambient air (without external encapsulation), whereas reference films degraded immediately. Building on these higher-quality films, the project fabricated NIR-LEDs that achieved a record peak external quantum efficiency (EQE) of 12.4%. Notably, the devices demonstrated measurable functionality in ambient air without external encapsulation (even though long-duration air operation remains a challenge for the broader field).
The project’s results go beyond the state of the art in two main ways. First, it establishes a design principle for tin-halide perovskite emitters: efficiency and stability are not improved by “removing doping at all costs”, but by balancing self-doping and trap densities so that radiative recombination is promoted while non-radiative pathways are suppressed. This perspective helps reconcile why strategies imported from photovoltaic perovskites (often aiming for intrinsic behavior) do not automatically translate to LEDs, especially in the deep-NIR regime. Second, the self-encapsulated thin-film strategy demonstrates that molecular design can simultaneously address multiple intrinsic bottlenecks of THPs (tin oxidation, film microstructure, traps, and inter-particle leakage pathways). The resulting NIR-LED performance—12.4% EQE—sets a new benchmark for tin-iodide perovskite LEDs and highlights a practical route toward air-tolerant processing. To accelerate uptake and success, key needs include: (i) further materials design to extend air operational stability from minutes/hours to device-relevant lifetimes, (ii) scale-up compatible coating strategies, and (iii) early engagement with manufacturing know-how and value chains for solution-processed emitters.