Prof Yen-Hung Lin

Abstract:

Metal-halide perovskite solar cells (PSCs) achieve high power-conversion efficiencies but remain susceptible to photo-induced degradation caused by mobile ions and phase segregation. Here, we investigate positional isomers of pyridine-carboxylic acid, namely pyridine-2-carboxylic acid (2-PC) and pyridine-4-carboxylic acid (4-PC), as anti-solvent additives to clarify how functional-group orientation governs defect passivation and photo-induced degradation. Both additives improve film morphology and reduce trap density; however, 4-PC, in which the carboxyl group is positioned opposite the pyridine nitrogen, provides markedly stronger passivation by virtue of its more favorable passivation geometry. As a result, 4-PC suppresses light-induced photoluminescence red shift, reduces trap density by approximately 27%, and enables unencapsulated devices to retain over 88% of their initial efficiency after 1000 h. Spectroscopic and transient analyses further indicate that 4-PC simultaneously passivates Pb-related defects and halide vacancies, thereby suppressing ion migration and halide phase segregation under operating conditions. These findings establish positional-isomer engineering as a practical molecular design principle for developing simple yet effective anti-solvent additives toward improved photo-induced phase stability in perovskite photovoltaics.

Abstract:

The development of highly efficient deep-blue fluorescent materials with Commission Internationale de l’Eclairage (CIE) coordinates approaching the BT.2020 standard in organic light-emitting diodes (OLEDs) is still a challenging task. Herein, two star-shaped near-ultraviolet/deep-blue emitters (BuCzI-2CN and BuCzI-3CN) possessing carbazole electron-donor moieties, cyano electron-acceptor groups, and an imidazole core are synthesized. Twisted and bipolar diphenyl-imidazole, carbazole and cyano moieties are linked through a benzene bridge to construct a steric structure for charge-balanced and stable near-ultraviolet emitters. Results show that the cyano acceptors enhance the electron transport capability successfully, while exhibiting saturated near-ultraviolet/deep-blue emission at 425 nm and 408 nm, along with the CIEy coordinates of 0.058 and 0.045 with high solid-state photoluminescence quantum yields of 50% and 42.3%, respectively. When incorporated into OLED devices, they show near-ultraviolet/deep-blue electroluminescence with CIEy coordinates ranging from 0.043 to 0.049 in solution-processed devices, matching the BT.2020 standard. Notably, the BuCzI-2CN based vacuum-processed OLED achieves a maximum external quantum efficiency (EQE) of 4.01%, a low turn-on voltage of 3.2 V, and a luminance of 3079 cd m⁻². These findings may provide new insights for the development of charge-balanced and highly efficient near-ultraviolet and deep-blue emitters.

Abstract:

Monolithic all-perovskite tandem solar cells (TSCs) offer a route beyond single-junction efficiency limits through band-gap engineering. However, stability is hampered by hygroscopic degradation and phase segregation of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), the most common hole-transport material for narrow band-gap subcells. Here, we investigate the interface-mediated crystallization dynamics in mixed tin-lead (Sn-Pb) perovskites through in situ studies. We find that solvent-underlayer synergetic interactions with PEDOT:PSS induce metastable phase segregation during crystallization. Replacing PEDOT:PSS with a phenothiazine-functionalized interface facilitates direct phase transition and achieves preferential (100) orientation, yielding high-quality perovskite films. This enables a single-junction narrow band-gap subcell with 23.2% efficiency. Furthermore, we apply a hybrid interlayer integrating thiol and phosphonic acid anchoring groups on SnO2/Au, achieving a dense interconnecting layer for monolithic all-perovskite TSCs with 29.1% efficiency. The device retains 90% of the initial efficiency over 800 h of maximum power point tracking under simulated 1-sun illumination at 40°C, demonstrating robust operational stability.

Abstract:

The commercialization of perovskite solar cells (PSCs) is bottlenecked by inefficient trial-and-error approaches reliant on human expertise in both materials discovery and device fabrication^1-3. Here we introduce an autonomous closed-loop framework that integrates machine learning (ML)-driven materials discovery with an automated manufacturing platform. The system uses active learning and quantum modelling to rapidly identify high-performance molecules and the platform uses Bayesian optimization and symbolic regression in a feedback loop to continuously refine the fabrication process. This integrated approach enabled the discovery of a passivation molecule, 5-(aminomethyl)nicotinonitrile hydroiodide (5ANI), which yielded 0.05-cm² solar cells with a power conversion efficiency (PCE) of 27.22% (certified maximum power point tracking (MPPT) efficiency of 27.18%) and 21.4-cm² mini-modules with a PCE of 23.49%. Moreover, the devices exhibited long-term operational stability, retaining 98.7% of their initial efficiency after 1,200 h of continuous operation under the ISOS-L-1I protocol. Crucially, the automated platform achieved an efficiency reproducibility nearly five times that of manual fabrication. This work establishes an automated closed-loop system that synergizes ML-powered discovery with the high-fidelity data from automated manufacturing, setting a benchmark for autonomous discovery and manufacturing in photovoltaics and materials.

Abstract:

All-inorganic perovskite solar cells (PSCs) have emerged as a prominent research focus because the high thermal/photo stability they can offer is critical to commercialization of the burgeoning photovoltaic (PV) technology. However, there remain issues pertaining to the susceptibility of the all-inorganic perovskites to surface degradation from moisture ingress under ambient conditions and the suboptimal PV efficiency that still lags substantially behind that of their organic-inorganic hybrid counterparts. To address these challenges, this work employs an in situ self-assembly strategy to construct a 1D/3D perovskite heterojunction on top of the all-inorganic perovskite using tetrabutylammonium trifluoromethanesulfonate (TTFS). While typical ammonium salts only provide a cationic barrier or weak passivation, the TTFS-based design uniquely synergizes a hydrophobic cationic barrier with strong anionic passivation, and concurrently creates fast electron extraction channels through a nanostructured interface. This approach overcomes the conventional trade-off between stability and efficiency. By exploiting it to optimize a semi-transparent wide-band PSC for 4-terminal (4-T) tandem devices, a certified power conversion efficiency (PCE) of 17.10% was achieved together with exceptional operational stability under maximum power point (MPP) tracking-maintaining 80% of the initial PCE (T₈₀) after operating for 1210 hours at 65 °C and 650 hours at 85 °C (ISOS-L-2). When it is combined with a narrow-band all-inorganic PSC in the 4-T tandem configuration, a certified efficiency of 21.54% was obtained, which is the highest reported for this type of tandem cells. Through synergistic optimization of interface stabilization and tandem optoelectronic management, this work provides valuable insights for developing efficient and stable all-inorganic perovskite tandem solar cells.