1. The project at a glance

The next generation of optoelectronics needs emerging semiconductors that combine high performance with low manufacturing costs. Lead halide perovskites are exceptional optoelectronic materials, but their success is held back by poor long-term stability. The MIX2FIX project (“Hybrid, organic-inorganic chalcogenide optoelectronics”) addresses this challenge by pioneering a new class of solution-processable optoelectronic devices based on air-stable, non-toxic metal chalcogenides combined with an organic component.

The core concept is to replace the halide framework of perovskites with a stable metal chalcogenide. This retains the ease of solution processing while giving the new compounds attractive optoelectronic properties. To raise the quality of these organic–inorganic hybrids, the project adapts proven optimisation strategies from perovskite technology, including trap passivation, control of crystal orientation, heterostructuring and interface engineering.

MIX2FIX thus develops new functional hybrids at the boundary between perovskite and chalcogenide thin-film technologies. By offering stable, competitive and eco-friendly alternatives, the project supports the transition towards green, sustainable optoelectronics for photovoltaics, light-emitting diodes and other advanced applications.

2. Objectives

MIX2FIX was designed around three ambitious, interrelated objectives:

• Objective 1: Design and develop a new class of eco-friendly, optoelectronically active organic–inorganic chalcogenide thin films, not explored before, by adapting crystallisation strategies from perovskite technology.
• Objective 2: Raise the optoelectronic quality of the new hybrids towards that of the best single-crystal semiconductors, such as GaAs, by optimising them for controllable charge separation, low defect densities and preferred crystal orientation.
• Objective 3: Integrate the optimised materials into solar cells and light-emitting diodes (LEDs) with efficiency and long-term stability comparable to, or higher than, those of lead halide perovskite or chalcopyrite devices.

3. Main achievements

Drawing on the hybrid organic–inorganic design of halide perovskites, MIX2FIX developed air-stable hybrid chalcogenides and advanced both material families in solar cells, LEDs and neuromorphic devices. More specifically:

• Dopant-free chalcogenide solar cells: We systematically optimised dopant-free P3HT hole-transport layers in planar Sb₂S₃ solar cells. This showed that polymer concentration critically governs charge-carrier dynamics, and the optimised cells reached a competitive power conversion efficiency of 5.2%.
• Heavy-metal-free quantum dots and LEDs: Formamidinium acetate engineering raised the photoluminescence quantum yield of shell-free CuInS₂ quantum dots to 94%, enabling efficient deep-red LEDs. We also developed a direct, low-temperature synthesis of device-grade Zn-alloyed AgIn₅S₈ inks. In AgInS₂/ZnS LEDs, FABr interlayers overcame the hole-injection bottleneck and significantly improved both external quantum efficiency and operational stability.
• Retina-inspired optoelectronic synapses: Iodide-capped PbS nanocrystal arrays operated as optoelectronic inhibitory synapses across the visible (RGB) spectrum. They reproduced key biological synaptic behaviours at low energy (~40 nJ per event), a step towards artificial visual processing.

In parallel, the project returned to the halide perovskites that inspired it, applying new surface-chemistry and interface-engineering strategies to improve their efficiency, stability and use in neuromorphic devices:

• Defect passivation in perovskites: A post-treatment with a thiol-functionalised tertiary ammonium halide (DEAET) regulated residual PbI₂ at FAPbI₃ surfaces, giving solar cells with efficiencies up to 21% and high operational stability. Mitigating residual FAI yielded efficient FAPbI₃ LEDs that remained stable for 15 days unencapsulated in air, while in situ polystyrene ligands gave CsPbBr₃ quantum dots with near-unity emission efficiency and improved moisture stability.
• High-endurance, ultralow-power optoelectronic memristors: We developed reconfigurable FA₂PbI₄/SiO₂ bilayer memristors and flexible 2D perovskite crossbar arrays, using non-destructive gas-phase condensation to soft-land Ag and Pt nanoparticles. This interface engineering delivered endurance above 10¹¹ switching cycles and energy consumption as low as ~10 fJ per spike.
• Multimodal reservoir computing: Low-power perovskite memristors were integrated into fused reservoir computing architectures that emulate biological multisensory processing, enabling real-time audio-visual processing and 84% accuracy in multicolour image recognition. Lead-free perovskite sensory neurons further extended this approach to neuromorphic visual perception.

4. Publications

A selection of the most important publications from the project:

1. Orfanoudakis, S.; Dallas, P.; Zacharopoulos, N.; Tsipas, P.; Banis, A.; Tsetseris, L.; Kontos, A. G.; Stergiopoulos, T. Shell-Free CuInS₂ Nanocrystals with Near-Unity Photoluminescence for Deep-Red LEDs. ACS Appl. Opt. Mater. 2026, 4 (1), 140–147. https://doi.org/10.1021/acsaom.5c00499
2. Theofylaktos, L.; Kalafatis, A.; Harlaftis, F.; Orfanoudakis, S.; Symeonidou, E.; Karnachoriti, M.; Mavropoulis, A.; Dimitrakis, P.; Banis, A.; Oikonomopoulos, P.; Bousoulas, P.; Kontos, A. G.; Stergiopoulos, T. Impact of P3HT Hole Transport Layer Thickness on Carrier Dynamics in Sb₂S₃ n–i–p Planar Solar Cells. J. Phys.: Energy 2026, 8 (2), 025002. https://doi.org/10.1088/2515-7655/ae5a01
3. Dallas, P.; Tzitzios, V. K.; Givalou, L.; Tsipas, P.; Basina, G.; Sakellis, E.; Boukos, N.; Stergiopoulos, T. Effects of Ligand Coordination on Ag₈SnS₆ as a Photoabsorber for Thin Film Solar Cells. J. Mater. Chem. C 2025, 13 (16), 7996–8005. https://doi.org/10.1039/d5tc00397k
4. Orfanoudakis, S.; Dimitriadi, M.; Zacharopoulos, N.; Banis, A.; Kontos, A. G.; Sakellariou, G.; Stergiopoulos, T. Stable, Near-Unity-PLQY CsPbBr₃ QDs by In Situ Hydroxyl-Terminated Polystyrene Ligands. ChemNanoMat 2026, 12 (5), e202600015. https://doi.org/10.1002/cnma.202600015
5. Orfanoudakis, S.; Yannakopoulou, K.; Morat, J.; Tsetseris, L.; Tsipas, P.; Skorda, S.; El Sachat, A.; Gao, F.; Kontos, A. G.; Stergiopoulos, T. Mitigating Residual FAI for Air-Stable FAPbI₃ LEDs. Small 2026. [https://doi.org/10.1002/smll.75332]
6. Orfanoudakis, S.; Gkini, K.; Harlaftis, F.; Tsipas, P.; Yannakopoulou, K.; Kontos, A. G.; Stergiopoulos, T. Thiol-Bearing Tertiary Alkylammonium Chloride for Regulation of PbI₂ Excess in FAPbI₃ Perovskite Solar Cells. ACS Appl. Energy Mater. 2026, 9 (7), 4005–4015. https://doi.org/10.1021/acsaem.6c00017
7. Bousoulas, P.; Orfanoudakis, S.; Tsetseris, L.; Tsioustas, C.; Skorda, S.; El Sachat, A.; Tsipas, P.; Kontos, A. G.; Stergiopoulos, T.; Tsoukalas, D. Low-Power Perovskite-Based Memristors Enable Fused Reservoir Computing and Neuromorphic Vision with Highly Accurate Color Perception. Small 2026, 22 (4). https://doi.org/10.1002/smll.202508167
8. Bousoulas, P.; Orfanoudakis, S.; Spathi, D.; Pagonis, V.; Tsetseris, L.; Tsioustas, C.; Tsipas, P.; Kontos, A. G.; Stergiopoulos, T.; Tsoukalas, D. Low Power FA₂PbI₄/SiO₂ Bilayer Memristors with Pt Nanoparticles Exhibiting Reconfigurable Synaptic and Neuron Properties for Compact Optoelectronic Neuromorphic Systems. Nano Lett. 2025, 25 (41), 14903–14912. https://doi.org/10.1021/acs.nanolett.5c03475
9. Bousoulas, P.; Orfanoudakis, S.; Tsioustas, C.; Vartian, R.; Cheliotis, I.; Oikonomopoulos, P.; Tsipas, P.; Spathi, D.; Kontos, A. G.; Zergioti, I.; Stergiopoulos, T.; Tsoukalas, D. Interfacial Engineering of Two-Dimensional Perovskite Memristors toward Reliable and Flexible Optoelectronic Memory Arrays. ACS Appl. Mater. Interfaces 2026, 18 (13), 19315–19326. https://doi.org/10.1021/acsami.6c00377
10. Bousoulas, P.; Orfanoudakis, S.; Tsioustas, C.; Galanos, A.; Zacharopoulos, N.; Stergiopoulos, T.; Tsoukalas, D. Neuromorphic Visual Perception through Multifunctional Lead-Free Perovskite Sensory Neurons. ACS Appl. Electron. Mater. 2026. https://doi.org/10.1021/acsaelm.6c01556.

5. Impact

MIX2FIX showed that the design principles behind the success of halide perovskites can be transferred to air-stable, less toxic metal chalcogenides, opening a route to solution-processable optoelectronics that avoids the stability drawbacks of lead-based perovskites. The project established that organic ligands and interface engineering can raise heavy-metal-free chalcogenide quantum dots to near-unity emission efficiency, making them credible candidates for next-generation displays and lighting. It also showed that low-temperature, ink-based processing can deliver device-grade chalcogenide films and nanocrystals for solar cells and LEDs.

Beyond its original scope, the project opened a new direction in light-driven neuromorphic hardware: electronic components that mimic how the brain processes information. Its perovskite and chalcogenide optoelectronic synapses and memristors combine very low energy consumption with high endurance, addressing one of the key bottlenecks of artificial intelligence: the energy cost of processing visual and sensory data. The perovskite work also fed back into the perovskite field itself through new surface treatments that improve both efficiency and stability.

By combining non-toxic emitters with bio-inspired hardware that operates at ultralow energies, the project responds directly to the growing societal and industrial demand for sustainable, energy-efficient electronics, laying the groundwork for greener next-generation smart technologies.

6. Acknowledgement

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 818615, MIX2FIX).