Engineering topics
Wang, Jiantao
Publications and source records attributed to Wang, Jiantao.
Sustainable materials acceleration platform reveals stable and efficient wide-bandgap metal halide perovskite alloys
The vast chemical space of emerging semiconductors, like metal halide perovskites, and their varied requirements for semiconductor applications have rendered trial-and-error environmentally unsustainable. Here, in this work, we demonstrate RoboMapper, a materials acceleration platform (MAP), that achieves 10-fold research acceleration by formulating and palletizing semiconductors on a chip, thereby allowing high-throughput (HT) measurements to generate quantitative structure-property relationships (QSPRs) considerably more efficiently and sustainably. We leverage the RoboMapper to construct QSPR maps for the mixed ion FA 1-y Cs y Pb(I 1-x Br x ) 3 halide perovskite in terms of structure, bandgap, and photostability with respect to its composition. We identify wide-bandgap alloys suitable for perovskite-Si hybrid tandem solar cells exhibiting a pure cubic perovskite phase with favorable defect chemistry while achieving superior stability at the target bandgap of ~1.7 eV. RoboMapper’s palletization strategy reduces environmental impacts of data generation in materials research by more than an order of magnitude, paving the way for sustainable data-driven materials research.
Enhancing Photostability of Sn-Pb Perovskite Solar Cells by an Alkylammonium Pseudo-Halogen Additive
High-performance tin-lead perovskite solar cells (PSCs) are needed for all-perovskite-tandem solar cells. However, iodide related fast photodegradation severely limits the operational stability of Sn-Pb perovskites despite the demonstrated high efficiency and thermal stability. Herein, this work employs an alkylammonium pseudo-halogen additive to enhance the power conversion efficiency (PCE) and photostability of methylammonium (MA)-free, Sn-Pb PSCs. Density functional theory (DFT) calculations reveal that the pseudo-halogen tetrafluoroborate (BF 4 - ) has strong binding capacity with metal ions (Sn 2+ /Pb 2+ ) in the Sn-Pb perovskite lattice, which lowers iodine vacancy formation. Upon combining BF 4 - with an octylammonium (OA + ) cation, the PCE of the device with a built-in light-scattering layer is boosted to 23.7%, which represents a new record for Sn-Pb PSCs. The improved efficiency benefits from the suppressed defect density. Under continuous 1 sun illumination, the OABF 4 embodied PSCs show slower generation of interstitial iodides and iodine, which greatly improves the device photostability under open-circuit condition. Moreover, the device based on OABF 4 retains 88% of the initial PCE for 1000 h under the maximum-power-point tracking (MPPT) without cooling.
Bifacial all-perovskite tandem solar cells
The efficiency of all-perovskite tandem devices falls far below theoretical efficiency limits, mainly because a widening bandgap fails to increase open-circuit voltage. We report on a bifacial all-perovskite tandem structures with an equivalent efficiency of 29.3% under back-to-front irradiance ratio of 30. This increases energy yield and reduces the required bandgap of a wide-bandgap cell. Open-circuit voltage deficit is therefore minimized, although its performance under only front irradiance is not ideal. The bifacial device needs a sputtered rear transparent electrode, which could reduce photon path length and deteriorate stability of Pb-Sn perovskites. Embedding a light-scattering micrometer-sized particle layer into perovskite to trap light, effectively increases absorptance by 5 to 15% in the infrared region. Using a nonacidic hole transport layer markedly stabilizes the hole-extraction interface by avoiding proton-accelerated formation of iodine. These two strategies together increase efficiency of semitransparent Pb-Sn cells from 15.6 to 19.4%, enabling fabrication of efficient bifacial all-perovskite tandem devices.
Solution Processed Ternary Tin (II) Alloy as Hole–Transport Layer of Sn–Pb Perovskite Solar Cells for Enhanced Efficiency and Stability
Tin-lead (Sn-Pb) narrow bandgap (NBG) perovskites show great potential in both single-junction and all-perovskite tandem solar cells. Sn-Pb perovskite solar cells (PSCs) are still limited by low charge collection efficiency and poor stability. Here, we report a ternary Sn (II) alloy of SnOCl as the hole-transport material (HTM) with a work function of 4.95 eV for Sn-Pb PSCs. The solution processed SnOCl layer has a texture structure which not only reduces the optical loss of the devices but also changes grain growth of Sn-Pb perovskites and boosts the carrier diffusion length to 3.63 μm. The formation of small perovskite grains at the HTM/perovskite interface is suppressed. These result in an almost constant internal quantum efficiency of 96 ± 2% across the absorption spectrum of Sn-Pb perovskites. The SnOCl HTM significantly enhances the stability of Sn-Pb PSCs with 87% of its initial efficiency retained after 1-sun illumination for 1,200 h, and keep 85% efficiency under 85°C thermal stress for 1,500 h. Furthermore, the hybrid HTM further improve the stabilized efficiencies of single-function Sn-Pb PSCs and all-perovskite tandem solar cells to 23.2% and 25.9%, respectively. This discovery opens an avenue to the multi-component metal alloys as HTM in PSCs.
Carbazole-Based Hole Transport Polymer for Methylammonium-Free Tin-Lead Perovskite Solar Cells with Enhanced Efficiency and Stability
As the most commonly used hole transport material (HTM) in tin-lead (Sn-Pb) perovskite solar cells (PSCs), poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) limits the power conversion efficiency (PCE) and stability of the PSCs due to its acidic characteristics. Herein, an easily synthesized polymer HTM poly[(phenyl)imino[9-(2-ethylhexyl)carbazole]-2,7-diyl] (CzAn) with a shallow highest occupied molecular orbital (HOMO) level of -4.95 eV is used in a p-i-n structure, methylammonium-free, Sn-Pb PSC to replace PEDOT:PSS. Upon optimization using doping and surface engineering, high quality Sn-Pb PSCs could be successfully fabricated, boosting the PCE to 22.6% (stabilized PCE of 21.3%) compared with 21.2% for PEDOT:PSS. The perovskite films prepared on the modified CzAn HTM possess improved crystallinity, reduced trap-state density, and larger carrier mobility resulting in PSCs with greatly improved stability.
A universal wet-chemistry synthesis of solid-state halide electrolytes for all-solid-state lithium-metal batteries
Solid-state halide electrolytes have gained revived research interests owing to their high ionic conductivity and high-voltage stability. However, synthesizing halide electrolytes from a liquid phase is extremely challenging because of the vulnerability of metal halides to hydrolysis. In this work, ammonium-assisted wet chemistry is reported to synthesize various solid-state halide electrolytes with an exceptional ionic conductivity (>1 microsiemens per centimeter). Microstrain-induced localized microstructure change is found to be beneficial to lithium ion transport in halide electrolytes. Furthermore, the interfacial incompatibility between halide electrolytes and lithium metal is alleviated by transforming the mixed electronic/ionic conductive interface into a lithium ion–conductive interface. Such all-solid-state lithium-metal batteries (ASSLMBs) demonstrate a high initial coulombic efficiency of 98.1% based on lithium cobalt oxide and a high discharge capacity of 166.9 microampere hours per gram based on single-crystal LiNi 0.6 Mn 0.2 Co 0.2 O 2 . This work provides universal approaches in both material synthesis and interface design for developing halide-based ASSLMBs.
Deciphering Interfacial Chemical and Electrochemical Reactions of Sulfide-Based All-Solid-State Batteries
Large interfacial resistance resulting from interfacial reactions is widely acknowledged as one of the main challenges in sulfide electrolytes (SEs)-based all-solid-state lithium batteries (ASSLBs). However, the root cause of the large interfacial resistance between the SEs and typical layered oxide cathodes is not fully understood yet. Here we deciphered that interfacial oxygen loss from single-crystal LiNi 0.5 Mn 0.3 Co 0.2 O 2 (SC-NMC532) chemically oxidizes Li 10 GeP 2 S 12 , generating oxygen-containing interfacial species. Meanwhile, the interfacial oxygen loss also induces a structural change of oxide cathodes (layered-to-rocksalt). Besides, the high operation voltage can electrochemically oxidize SEs to form non-oxygen species (e.g. polysulfides). These chemically and electrochemically oxidized species, together with the interfacial structural change, are responsible for the large interfacial resistance at the cathode interface. More importantly, the widely adopted interfacial coating strategy is effective in suppressing chemically oxidized oxygen-containing species and mitigating the coincident interfacial structural change but is unable to prevent electrochemically induced non-oxygen species. These findings provide a deeper insight into the large interfacial resistance between the typical SE and layered oxide cathodes, which may be of assistance for the rational interface design of SE-based ASSLBs in future.