Photovoltaic & Optoelectronic Device Group

Abstract:

All-inorganic CsPbI₃ perovskite nanocrystals (PNCs) have emerged as promising emitters for optoelectronic applications owing to their high color purity, tunable bandgap, and high photoluminescence quantum yield (PLQY). However, dynamic surface ligands, abundant trap states, and rapid halide ion migration limit their emission efficiency and operational stability. Here, methylammonium (MA⁺), formamidinium (FA⁺), and guanidinium (GA⁺) were systematically investigated as surface modulators for PNCs via an anti-solvent-assisted post-treatment strategy. Spectroscopic analyses and density functional theory calculations reveal that the passivation efficacy is determined by the strength and denticity of hydrogen-bonding interactions between the organic cations and the PNC surface. Among the three candidates, GA⁺ exhibits the highest efficacy owing to its trifunctional N─H groups, which enable robust multidentate surface interactions that suppress trap formation and halide ion migration. As a result, GA-treated PNCs achieve a PLQY of 99.3% and retain ∼80% of their initial PLQY after 9 days under ambient conditions. The resulting perovskite light-emitting diodes deliver a maximum external quantum efficiency of 10.2% and a maximum luminance of 473 cd m^-2, representing a significant improvement over pristine devices. These findings identify molecular hydrogen-bonding geometry as a key design parameter for surface engineering of efficient and stable PNC-based optoelectronic devices.

Abstract:

The practical application of perovskite nanocrystals has been hindered by their intrinsic instability, arising from the coupled effects of soft ionic lattices, ion migration, and surface reactions. A hierarchical shell strategy now addresses these intertwined degradation pathways through lattice-interface “interlocking”, achieving T90 values exceeding 27,000 h under continuous blue-light exposure. Notably, the resulting hierarchical shell-perovskite nanocrystals enable reliable colour-conversion display prototypes.

Abstract:

We investigate the impact of employing fullerene self-assembled monolayers (SAMs) in conjunction with SnO2 electron-transport layers (ETLs) in negative–intrinsic–positive (n–i–p) perovskite solar cells. We compare the efficacy of the fullerene-SAM surface-binding group—carboxylic or phosphonic acid—on the passivation, charge transport, and energetics of the modified-SnO2 surface. Planar n–i–p perovskite solar cells with these SAM-modified SnO2 exhibit significantly reduced hysteresis, and the steady-state maximum power point tracked efficiencies (η MPP) of the devices improved from an average of 18.6–20.0% comparing devices with neat SnO2 to the C60-PA SAM inclusion, respectively. While C60-PA SAM improved the initial solar cell efficiency, this benefit was not maintained during light exposure at elevated temperatures as the fullerene SAM weakened adhesion at the perovskite/metal oxide interface in the aged devices. These results highlight the importance of improving the mechanical robustness of perovskite/charge-transport layer interfaces under operational aging conditions.

Abstract:

ABSTRACT The development of stable and spectrally pure green emitters remains a critical challenge for high performance full color displays and solid‐state lighting. In this work, we present a simple and effective approach to fabricate perovskite light‐emitting diodes based on CsPbBr 3 quantum dots confined within a nanoporous silica scaffold. The introduction of linear (n) or branched (t) butylammonium bromide and crown ethers into the precursor solution prior to infiltration induces improved charge injection and transport across the active layer. This dual‐additive approach contributes to a dramatic enhancement in device performance, leading to a highest luminance exceeding 10,000 cd m − 2 , and markedly improved operational stability. The optimized devices exhibit ultrapure green emission centered at 520 nm with a narrow spectral width below 20 nm. The proposed method provides a versatile and scalable route toward bright, spectrally pure, and durable perovskite light‐emitting devices.

Abstract:

ABSTRACT Perovskite solar cells have achieved high efficiencies but remain limited by instabilities. For the opaque metal rear electrode, Au is commonly used to achieve stable operation but is impractical for scalable photovoltaics due to cost. We investigate the effect of a 5 nm chromium (Cr) interlayer beneath low‐cost metals (Al, Ag, Cu) to inhibit metal interdiffusion. Cr/Al electrodes yield devices with high efficiencies (up to 24.7%) and operational stability comparable to reference devices using Au rear electrodes under heat and light stress, with raw material costs reduced by five orders of magnitude. At the front semi‐transparent electrode, through which sunlight will be incident, we identify indium diffusion from indium tin oxide (ITO) as a key degradation mechanism, revealed via depth‐resolved mass spectrometry. We demonstrate that replacing ITO with fluorine‐doped tin oxide (FTO) substantially improves stability. Combining both improvements, FTO with Cr/Al contacts, produces devices retaining >66% of the initial efficiency after >1000 h ageing at 75 °C under simulated sunlight. These results highlight the critical role of electrode selection on perovskite solar cell durability and provide a practical route toward stable and cost‐effective perovskite photovoltaics.