Chen Weijie

Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Jiachen Xi, Yeyong Wu, Weijie Chen, Qilong Li, Jiajia Li, Yunxiu Shen, Haiyang Chen, Guiying Xu, Heyi Yang, Ziyuan Chen, Na Li, Jian Zhu, Yaowen Li, Yongfang Li

An up-conversion nanoparticles and Mn^II-based perovskite core–shell heterostructures nanocomposite was successfully synthesized for the first time, which showed dual-color emissions under the excitation of UV light and IR laser. This work suggests its potential in high-quality optical anticounterfeiting.

Abstract

In view of their excellent luminescence properties, nanocrystalline metal halide perovskites have diverse optoelectronic applications, including those related to anticounterfeiting. However, high-quality optical anticounterfeiting typically requires multiple encryptions relying on several optical modes to ensure information security. Herein, an efficient anticounterfeiting strategy based on dual optical encryption is realized by combining up- and downconversion luminescence in a nanocomposite with NaYF₄ : Er³⁺,Yb³⁺ as core and a CsMnCl₃ as shell. The emission color of this nanocomposite depends on the penetration depth of incident radiation and can be changed by varying the excitation source (980 nm laser or UV light) to produce different luminescent patterns. This feature allows one to effectively improve the anticounterfeiting index and fabricate professional anticounterfeiting materials.

A molecularly engineered cyclobutane-based hole-transporting material synthesised using simple and green-chemistry-inspired protocols achieves an impressive efficiency of 21 % in perovskite solar cells and over 19 % in perovskite solar module with an active area of 30.24 cm².

Abstract

Hybrid lead halide perovskite solar cells (PSCs) have emerged as potential competitors to silicon-based solar cells with an unprecedented increase in power conversion efficiency (PCE), nearing the breakthrough point toward commercialization. However, for hole-transporting materials, it is generally acknowledged that complex structures often create issues such as increased costs and hazardous substances in the synthetic schemes, when translated from the laboratory to manufacture on a large scale. Here, we present cyclobutane-based hole-selective materials synthesized using simple and green-chemistry inspired protocols in order to reduce costs and adverse environmental impact. A series of novel semiconductors with molecularly engineered side arms were successfully applied in perovskite solar cells. V1366-based PSCs feature impressive efficiency of 21 %, along with long-term operational stability under atmospheric environment. Most importantly, we also fabricated perovskite solar modules exhibiting a record efficiency over 19 % with an active area of 30.24 cm².

Nature Energy, Published online: 16 December 2021; doi:10.1038/s41560-021-00953-z

Nature Energy, Published online: 16 December 2021; doi:10.1038/s41560-021-00944-0

The excellent suitability of bilayer organic photovoltaic devices for efficient indoor-light harvesting is demonstrated. Thanks to ideal interfacial contacts between photoactive and charge transport layers and minimized isolated donor and/or acceptor domains, bilayer devices show much smaller open-circuit voltage loss and high shunt resistance, leading to enhanced fill factor and max power output without light soaking.

Abstract

Indoor organic photovoltaics (OPVs) are a potential niche application for organic semiconductors due to their strong and well-matched absorption with the emission of indoor lighting. However, due to extremely low photocurrent generation, the device parameters critical for efficient indoor OPVs differ from those under 1 Sun conditions. Herein, these critical device parameters—recombination loss and shunt resistance (R _sh)—are identified and it is demonstrated that bilayer OPVs are suitable for indoor PV applications. Compared to bulk-heterojunction (BHJ), the open-circuit voltage loss of bilayer devices under low light intensities is much smaller, consistent with a larger surface photovoltage response, indicating suppressed recombination losses. The bilayer devices show a higher fill factor at low light intensities, resulting from high R _sh afforded by the ideal interfacial contacts between the photoactive and the charge transport layers. The high R _sh enables bilayer devices to perform well without a light-soaking process. Finally, the charge carriers are extracted rapidly in bilayers, which are attributed to strongly suppressed trap states possibly induced by isolated domains and non-ideal interfacial contacts in BHJs. This study highlights the excellent suitability of bilayer OPVs for indoor applications and demonstrates the importance of device architecture and interfacial structures for efficient indoor OPVs.

The buried ionic liquid functional layer provides electron-rich environment for the perovskite growth to suppress Sn²⁺ oxidation, resulting in improved bulk crystallinity. Consequently, a high efficiency of 11.28% is obtained for the inorganic CsPb_0.75Sn_0.25I₂Br perovskite solar cells (PSCs).

The enlightening inorganic Sn-based metal halide perovskites hold promise for environment-friendly and efficient energy conversion. However, the undesired Sn²⁺ oxidation and uncontrollable crystallization of the perovskite absorber slow the development of highly efficient Sn-based inorganic perovskite solar cells. Herein, an ionic liquid layer of 1-butylpyridinium bromide (BPB) is employed as a buried functional template for the growth of the inorganic CsPb_0.75Sn_0.25I₂Br perovskite absorber. The buried functional layer provides lone electron pairs from N atom to coordinate with the unsaturated metal ions (Pb and Sn) via the coupling effect. In addition, the electronegative atom from the hydrogen bond acceptor offers an electron-rich environment for the perovskite growth to suppress Sn²⁺ oxidation. More importantly, this positive effect transduces from the interface to the bulk perovskite growth, leading to enhanced crystallinity and thus reduced nonradiative trap defects. Consequently, the efficiency of the inorganic CsPb_0.75Sn_0.25I₂Br PSCs is improved from 6.80% to 11.28%, and the unencapsulated device exhibits superior ambient stability, maintaining 62% of its initial power conversion efficiency in dried air for 200 h. The buried ionic liquid functional layer approach provides an avenue for the development of high-efficiency Sn-based optoelectronics.

The resistance of perovskite solar cells (PSC) to potential induced degradation (PID) is investigated by the help of I–V curve, electroluminescence, external quantum efficiency measurements, and secondary ion mass spectrometry. The PSCs are PID proof when they are exposed to current system voltages but degrade very fast if they are exposed to a high voltage of −1000 V.

Potential-induced degradation (PID) is a solar cell-related degradation mechanism due to high potential difference in a photovoltaic (PV) module between the solar cells and its grounded frame. This type of degradation is well known for silicon PV; however, for perovskites it has not been thoroughly researched yet. Herein, the PID of perovskite solar cells is investigated for bias voltages of ±500 V, half of the currently used system voltage, and ±1000 V with regular I–V and electroluminescence measurements during the test. The devices show a high PID resistance under applied bias of ±500 V, far exceeding the recommended guidelines for silicon PV. However, for the bias voltage of –1000 V a rapid degradation is observed due to the ingress of sodium ions from the glass substrate as confirmed by the time-of-flight secondary ion mass spectrometry measurements of spatial and depth distribution of elements in solar cells. Positively biased devices show no degradation due to high voltage exposure. These results show promising signs that perovskite solar cells are PID proof for current PV system designs.

A new D–π–A-type Zinc zinc pyridine porphyrin derivative (ZnPP) is synthesized and used as a graded passivation molecular for modifying the perovskite solar cell (PSC). It is found that ZnPP treatment significantly improves the quality of perovskite films and passivates the defects, yielding devices with a high efficiency of 21.08% with fill factor (FF) of 82.91

While perovskite solar cells (PSCs) have recently experienced a rapid rise in power conversion efficiency (PCE), the prevailing PSCs still contain nondesirable defects in the interior and interface of the perovskite layer, which limits further enhancement in PCE and device stability. Herein, a new D–π–A-type zinc pyridine porphyrin derivative (ZnPP) is synthesized and used as a passivation molecular via the antisolvent process for modifying the typical perovskite bulk thin film, leading to a new type of PSC with a graded passivation of the perovskite layer. Impressively, it is found that ZnPP treatment significantly improves the quality of perovskite films and reduces charge transport losses through passivating the uncoordinated Pb²⁺ cations, yielding devices with a high efficiency of 21.08% with fill factor (FF) of 82.91% and demonstrating the promise of integration of perovskite bulk thin films with tailor molecular via graded modification.

Herein, a simple dynamic vacuum-assisted low-temperature engineering is developed to prepare high quality CsPbIBr₂ film (VALT-CsPbIBr₂ film). The derived VALT-CsPbIBr₂ PSCs yield a superior PCE of 11.01% with a remarkable fill factor of 75.31%, which both are impressive among the reported CsPbIBr₂ PSCs. Meanwhile, VALT-CsPbIBr₂ PSCs feature stronger endurance against heat and moisture than control ones.

Among all-inorganic perovskite photoactive materials, CsPbIBr₂ demonstrates the most balanced trade-off between optical bandgap and phase stability. However, the poor quality and high-temperature engineering of CsPbIBr₂ film hinder the further optimization of derived perovskite solar cells (PSCs). Herein, a simple dynamic vacuum-assisted low-temperature engineering (merely 140 °C) is proposed to prepare high-quality CsPbIBr₂ film (VALT-CsPbIBr₂ film). Compared to HT-CsPbIBr₂ film processed via conventionally high temperature (280 °C), VALT-CsPbIBr₂ film presents higher crystallinity and more full coverage consisting of larger grains and fewer grain boundaries, which results in intensified light-harvesting capability, reduced defects, and extended charge carrier lifetime. Benefiting from those improved merits, VALT-CsPbIBr₂ PSCs show lower trap-state densities, more proficient charge dynamics, and larger built-in potential than HT-CsPbIBr₂ PSCs. Consequently, VALT-CsPbIBr₂ PSCs deliver a higher efficiency of 11.01% accompanied by a large open-circuit voltage of 1.289 V and a remarkable fill factor of 75.31%, being highly impressive among those reported CsPbIBr₂ PSCs. By contrast, the efficiency of HT-CsPbIBr₂ PSCs is only 9.00%. Moreover, VALT-CsPbIBr₂ PSCs present stronger endurance against heat and moisture than HT-CsPbIBr₂ PSCs. Herein, a feasible avenue to fabricate efficient yet stable all-inorganic PSCs via low-temperature engineering is provided.

Based on theoretically calculated Gibbs free energies (∆G) of Cs-Pb-Br derivatives, the 0D Cs₄PbBr₆ phase is suppressed by optimizing the fabrication method, delivering a champion efficiency of 10.67% for all-inorganic CsPbBr₃ PSC.

Abstract

The precise phase control of Cs-Pb-Br derivatives from 3D CsPbBr₃ to 0D Cs₄PbBr₆ highly determines the photovoltaic performance of all-inorganic CsPbBr₃ perovskite solar cells (PSCs). Herein, the preferred phase conversion from precursor to Cs-Pb-Br derivatives is revealed by theoretically calculating the Gibbs free energies (∆G) of various phase conversion processes, allowing for a simplified multi-step solution-processable spin-coating method to hinder the formation of detrimental 0D Cs₄PbBr₆ phase and enhance the photovoltaic performance of a PSC because of its large exciton binding energy, which is regarded as a recombination center. By further accelerating the interfacial charge extraction with a novel 2D transition metal dichalcogenide ReSe₂, the hole-free CsPbBr₃ PSC achieves a champion efficiency of 10.67% with an impressive open-circuit voltage of 1.622 V and an excellent long-term stability. This work provides an in-depth understanding on the precise Cs-Pb-Br perovskite phase control and the effect of derivatives on photovoltaic performance of advanced CsPbBr₃ PSCs.

A novel local Hubbard U method resolves challenges in simulating defected semi-conducting oxides under electric field. This approach reveals that the oxygen vacancy dipole moment correlates positively with lattice volume and B-site cation electronegativity. The predicted relationships among point defect polarization, mechanical strain, and transition metal chemistry provide insights for properties of memristive materials and devices under high electric fields.

Abstract

Polarization of ionic and electronic defects in response to high electric fields plays an essential role in determining properties of materials in applications such as memristive devices. However, isolating the polarization response of individual defects has been challenging for both models and measurements. Here the authors quantify the nonlinear dielectric response of neutral oxygen vacancies, comprised of strongly localized electrons at an oxygen vacancy site, in perovskite oxides of the form ABO₃. Their approach implements a computationally efficient local Hubbard U correction in density functional theory simulations. These calculations indicate that the electric dipole moment of this defect is correlated positively with the lattice volume, which they varied by elastic strain and by A-site cation species. In addition, the dipole of the neutral oxygen vacancy under electric field increases with increasing reducibility of the B-site cation. The predicted relationship among point defect polarization, mechanical strain, and transition metal chemistry provides insights for the properties of memristive materials and devices under high electric fields.

Highly efficient state-of-the-art PM6:Y6 based organic solar cells with a ternary architecture are achieved, which feature a record efficiency of 18.13% and an impressive fill factor of 80.10%.

Abstract

Ternary architecture is an efficient strategy to boost desired power conversion efficiency of single-junction organic solar cells (OSCs). Here, a ternary OSC by incorporating a compatible acceptor ITIC-M as a third component into state-of-the-art PM6:Y6 blend is reported, yielding a power conversion efficiency of 18.13% and an impressive fill factor of 80.10%. The efficiency is the highest record for the PM6:Y6 based ternary devices reported to date. The full advantages of the designed ternary heterojunction are the good complementary light absorption that increases the photocurrent, and the matched interfacial electronic structures featuring so-called pinning energies that facilitate exciton separation and suppress charge recombination loss. Furthermore, ITIC-M plays a vital role in optimizing the micromorphology of the ternary blend with better dispersity, well-formed fibrillar structure and enhanced crystallinity, thus boosting the charge transport and device performance.

Nature Energy, Published online: 13 December 2021; doi:10.1038/s41560-021-00954-y

Nature Energy, Published online: 13 December 2021; doi:10.1038/s41560-021-00941-3

Spray deposited SnO₂ (spray-SnO₂) film enables a power conversion efficiency (PCE) of 20.1% for FAPbI₃-based perovskite solar cells (PSCs). The PSCs based on large-area (62.5 cm²) spray-SnO₂ films deposited on multiple substrates (S1–S10) display highly consistent PCE, manifesting its scalability potential.

Abstract

The performance and scalability of perovskite solar cells (PSCs) is highly dependent on the morphology and charge selectivity of the electron transport layer (ETL). This work demonstrates a high-speed (1800 mm min⁻¹), room-temperature (25 °C–30 °C) deposition of large-area (62.5 cm²) tin oxide films using a multi-pass spray deposition technique. The spray-deposited SnO₂ (spray-SnO₂) films exhibit a controllable thickness, a unique granulate morphology and high transmittance (≈85% at 550 nm). The performance of the PSC based on spray-SnO₂ ETL and formamidinium lead iodide (FAPbI₃)-based perovskite is highly consistent and reproducible, achieving a maximum efficiency of ≈20.1% at an active area (A) of 0.096 cm². Characterization results reveal that the efficiency improvement originates from the granular morphology of spray-SnO₂ and high conversion rate of PbI₂ in the perovskite. More importantly, spray-SnO₂ films are highly scalable and able to reduce the efficiency roll-off that comes with the increase in contact-area between SnO₂ and perovskite film. Based on the spray-SnO₂ ETL, large-area PSC (A = 1.0 cm²) achieves an efficiency of ≈18.9%. Furthermore, spray-SnO₂ ETL based PSCs also exhibit higher storage stability compared to the spin-SnO₂ based PSCs.

Semitransparent organic photovoltaics (ST-OPVs) have been receiving tremendous attention because they of their tunable energy levels and rising power conversion efficiency (PCE). The steady increase of the PCE with high transmittances in the visible range results from improvements of narrow-bandgap donors and acceptors. Moreover, advanced device structure designs with narrow-bandgap materials can further push the performance of ST-OPVs.

Abstract

Solar energy offers an alternative solution to the global community's growing energy demands. Semitransparent organic photovoltaics (ST-OPVs) have received tremendous attention due to their tunable energy levels and rising power conversion efficiency (PCE). Because of its transparency, ST-OPVs are able to serve as the power-generating roof of the greenhouse, and color-tunable walls/windows for modern buildings or façades. With the rapid development of narrow-bandgap semiconductors to absorb near-infrared photons, the performances of ST-OPVs has progressed with PCEs over 12% with average visible transmittances over 20%. Here, recent developments in ST-OPVs based on narrow-bandgap donors and non-fullerene acceptors are reviewed. Several strategies for chemical structures design have been reported to lower bandgaps semiconductor materials. The recent developments of non-fullerene acceptor structures for ST-OPVs are categorized into A-D-A, A-π-D-π-A, and A-DAD-A by the structure alignment. From device perspectives, the strategies such as ternary blend, distributions of donors and acceptors in active layers, tandem and transparent conductive electrodes for high-performance ST-OPVs are summarized. To conclude, some insightful guidelines for future developments in ST-OPVs from both materials and device points of views are provided.

Two small-molecule donors, SM-BF1 and SM-BF2, are synthesized by a low-cost synthesis route utilizing cheap raw materials. The champion device based on SM-BF1:Y6 shows a power conversion efficiency (PCE) of 15.71%, benefitted from its better miscible morphology and more balanced charge-carrier transport characteristics. Furthermore, through the figure of merit (FOM) analysis, SM-BF1 also shows a good prospect for commercial application.

Abstract

Low cost, high efficiency, and high stability are the three key issues of organic solar cells (OSCs) that should be carefully considered to meet the requirement of future commercial applications. Therefore, the development of high-performance organic photovoltaic materials with low synthetic cost has been becoming a crucial challenge in the field of OSCs. Herein, two new low-cost small-molecule donors (SM-BF1 and SM-BF2) are designed and synthesized with a facile synthetic route by replacing 4-bromo-2-fluorobenzenethiol and 4-bromo-3-fluorobenzenethiol with low-cost 4-bromo-2-fluoro-1-iodobenzene and 4-bromo-3-fluoro-1-iodobenzene as key raw materials. Besides, the influence of the chemical steric effect of the phenyl conjugated side chains of the benzodithiophene (BDT) unit on photophysical properties, charge transfer, and photovoltaic properties are deeply investigated by the modulation of fluorine atom substituted position. As a result, SM-BF1 with ortho-fluorinated substituent has outstanding crystallization properties and better miscibility with acceptor Y6 and exhibits more desirable morphology and more balanced charge-carrier transport properties, leading to a superior power conversion efficiency (PCE) to 15.71%. More encouragingly, according to the figure of merit (FOM) and the industrial figure of merit (i-FOM) to evaluate the small-molecule donors, the SM-BF1-based device has excellent potential for future commercial applications.