He Tingwei （何庭伟）

The ETL/perovskite interface is crucial for the photovoltaic performance of perovskite solar cells (PSCs) because of its key role in electrons transport and charge recombination. Herein, an ultrathin CaTiO3 layer has facilely been fabricated and incorporated between the mp-TiO2 and perovskite layers. Due to the trap passivation effect and the optimized energy level alignment induced by modification, the electron transport is facilitated while the charge recombination is suppressed effectively. Therefore, the champion device gains a maximum PCE of 19.12% with the enhanced photovoltaic performance. In addition, the stability of PSCs has also been ameliorated by modification, and about 85% of the initial efficiency can be maintained even after exposure in ambient for 1000h.

Owing to the easy migration of halogen ions in wide-bandgap perovskite, it will lead to the formation of a large number of uncoordinated Pb2+ to form deep-level defects, which seriously affects the power conversion efficiency (PCE) and stability of wide-bandgap perovskite solar cells (PSCs). The introduction of additives has been recognized as an effective method to improve these defects, especially Lewis acid-base additives. Herein, Lewis base molecule dibenzofuran (DBF) with π-conjugated system, which can form π-π stacked dimer, is used as a perovskite additive. The detailed crystallization process of perovskite main precursor triggered by DBF is measured by using laser scanning confocal microscopy. It is demonstrated that the addition of DBF in perovskite samples resulted in a deceleration of the crystallization process, which is due to the formation of Lewis acid-base complexes between DBF π-π stacked …

Wide‐bandgap mixed‐halogen perovskite materials are widely used as top cells in tandem solar cells. However, serious open‐circuit voltage (Voc) loss restricts the power conversion efficiency (PCE) of wide‐bandgap perovskite solar cells (PSCs). Herein, we show that the resulting methylammonium vacancies induce lattice distortion in methylammonium chloride‐assisted perovskite film, resulting in an inhomogeneous halogen distribution and low Voc. Thus, a lattice strain regulation strategy is reported to fabricate high‐performance wide‐bandgap PSCs. Rubidium (Rb) cations are introduced to fill the A‐site vacancy caused by the methylammonium volatilization, which alleviates shrinkage strain of the perovskite crystal. The reduced lattice distortion and increased halide ion migration barrier result in a homogeneous mixed‐halide perovskite film. Due to improved carrier transport and suppressed nonradiative …

Methylammonium chloride (MACl) additive is almost irreplaceable in high‐performance formamidine perovskite photovoltaics. Nevertheless, Some of the problems that can arise from adding MACl are rarely mentioned. Herein, it is proposed for the first time that the addition of MACl would cause the non‐stoichiometric ratio in the perovskite film, resulting in the halogen vacancy. It is demonstrated that the non‐synchronous volatilization of methylamine cations and chloride ions leads to the formation of halogen vacancy defects. To solve this problem, the NH4HCOO is introduced into the perovskite precursor solution to passivate the halogen vacancy. The HCOO− ions have a strong force with lead ions and can fill the halogen vacancy defects. Consequently, the champion devices' power conversion efficiency (PCE) can be improved from 21.23% to 23.72% with negligible hysteresis. And the unencapsulated device …

Electron transport layer (ETL) plays an important role in perovskite solar cells (PSCs). In this paper, a stable and cheap metal chelating agent, subnitrotriacetic acid (NTA), was used to modify SnO2 ETL in two ways:1) By incorporating NTA into SnO2 colloidal dispersion, the oxygen vacancy causing charge recombination was greatly reduced, and the recombination of psc was reduced by reducing the introduction of surface Ovs, 2) Spin-coating NTA at the SnO2/perovskite interface not only manages a large number of oxygen vacancies generated by high-temperature annealing, but also interacts with the unpaired Pb2+ in the perovskite absorption layer by interface modification of the Cdouble bondO bond in NTA, passivates the surface of the perovskite layer, inhibits ion migration, stabilize the perovskite structure, and avoid its collapse, while significantly reducing the defect state density. By inhibiting the shallow …

The hole transport layer (HTL)/anode interface plays an important role in high-performance regular Ag-based perovskite solar cells (PSCs). Usually, the charge barrier caused by the energy level mismatch at the HTL/Ag interface will lead to the abnormal s-type J-V curve, which seriously hindering the commercial application of Ag-based PSCs. Here, we introduce a solution processed molybdenum oxide (HxMoO3) into the HTL/Ag interface to form a double-hole HTL. The work function (WF) of HxMoO3 films can be adjusted by controlling the reaction time. The introduction of HxMoO3 can effectively change the energy-level bending orientation, promote the charge transport and suppresses carrier recombination, thus eliminate the s-type J-V curve. Finally, the Ag-based PSCs achieve a power conversion efficiency (PCE) of 23.16%. Meanwhile, the PCE of the four-terminal (4T) perovskite/silicon tandem cell reaches …

Organic-inorganic hybrid perovskite materials with distinctive optoelectronic properties have attracted much interest in the field of solar cells. As the light absorber, the quality of perovskite films is crucial to the performances of perovskite solar cells. Anti-solvent engineering seems to be an efficient method in preparing high-quality perovskite films, but mostly used anti-solvents are toxic, such as chlorobenzene (CB), which is harmful to the environmental protection. In the present work, we used the green anti-solvent diethyl carbonate (DEC) instead of CB, demonstrated that the DEC engineered CH3NH3PbI3 film exhibits improved morphology and crystallinity as well as reducing defects, which can be attributed to the interaction between DEC and the solvent dimethyl sulfoxide (DMSO). The DEC anti-solvent assisting yields efficient CH3NH3PbI3 perovskite solar cells with a champion power conversion efficiency of 20 …

Mixed halogen wide-bandgap perovskite materials are often applied to the top cells of tandem solar cells. Nevertheless, serious halogen vacancy defects in mixed halogen perovskite materials remain one of the main factors restricting the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Fluoride has been proposed to inhibit halogen vacancy defects, but fluoride-induced crystallization behaviour is not thoroughly understood in wide-bandgap mixed halide perovskite systems. Here, we introduce tetrafluoroborate ion (BF4−) into the wide-bandgap perovskite precursor solution to regulate the crystallization dynamics. Due to high electronegativity and strong electron affinity, a strong interaction between BF4− and the [PbX6]4− octahedron increases the formation energy of perovskite crystal, inhibiting perovskite nucleation. The reduced nucleation site slows down the crystallization rate of …

Formamidinium lead iodide (FAPbI3) perovskite possesses an ideal optical bandgap and is a potential material for fabricating the most efficient single‐junction perovskite solar cells (PSCs). Nevertheless, large formamidinium (FA) cations result in residual lattice strain, which reduces the power conversion efficiency (PCE) and operational stability of PSCs. Herein, the modulation of lattice strain in FAPbI3 crystals via a π‐conjugated organic amine, i.e., 4‐pyrene oxy butylamine (PYBA), is proposed. PYBA pairs at the grain boundary serve as a template for the crystallization of FAPbI3 perovskite, thereby inducing a highly oriented crystal and a pure α‐phase film. The PYBA pairs with strong π–π interactions provide a solid fulcrum for external compression strain, thus compensating for the inherent tension strain of FAPbI3 crystals. The strain release elevates the valence band of the perovskite crystals, thereby …

The perovskite photovoltaic field has developed rapidly within a decade. In particular, formamidinium (FA)‐rich perovskite allows a broad absorption spectrum, and is considered to be one of the most promising perovskite materials. Great progress has been achieved, and most recorded high‐efficient perovskite solar cells (PSCs) used the FA‐rich perovskite light absorption layer. However, the black α‐phase formamidinium lead iodide (FAPbI3) perovskite easily transforms into an undesirable δ‐phase at a low temperature. Thus, researchers have put a lot of effort into deeply understanding the phase transformation and stabilization mechanism of FA‐rich perovskite. Herein, the fundamental physical properties of FAPbI3 materials, including crystal structure, phase‐transition temperature, charge‐carrier dynamics, etc. are summarized, and establish a complete phase evolution with temperature by reviewing previous …

Organic–inorganic hybrid perovskite materials have attracted widespread attention in the photovoltaic field. The best‐certified perovskite single‐junction photovoltaics have achieved an impressive power conversion efficiency of 25.5%. Particularly, formamidinium lead triiodide (FAPbI3) perovskite material has been considered to be one of the most promising materials for fabricating highly efficient single‐junction solar cells due to its suitable bandgap (1.43 eV). However, the metastable α‐FAPbI3 perovskite phase, which can spontaneously transform into the undesirable δ phase, limits their further applications. Accordingly, stabilizing the α phase and achieving high‐quality films are keys for achieving high‐efficiency and long‐term operational perovskite photovoltaics. In this review, strategies for stabilization of α‐FAPbI3 are discussed in detail, and the corresponding thermodynamic mechanisms are also …

Quasi-two-dimensional halide perovskites are commonly used in solar cells, as they are more stable than their three-dimensional analogues. Nevertheless, it is still challenging to meet the stability requirements under high-humidity conditions. Here, we design π-conjugated carbazole (CA) cations to increase the water resistance of perovskite. We control the crystallization kinetics by the anti-solvent strategy to locate the hydrophobic low-⟨n⟩-value phase on the surface of the perovskite film. The resulting CA2MA4Pb5I16 film does not decompose after being immersed in water for several minutes. We further regulate the vertical orientation of perovskite crystals by introducing NH4SCN additive, resulting in improved carrier transport dynamics. As a result, the optimized CA2MA4Pb5I16 device achieves a notable power conversion efficiency (PCE) of 18.23% and retains more than 85% of the original PCE after 2000 h …

Quasi‐two‐dimensional (quasi‐2D) perovskite materials are widely applied in the photovoltaic field, since they exhibit more stable crystal structure than three‐dimensional (3D) analogs. Although quasi‐2D crystals possess excellent environmental stability, their layered structures hinder the out‐of‐plane carrier transport, which is not conducive to the realization of high‐efficiency photovoltaic devices. Thus it is necessary to balance the stability and the efficiency through some strategies. In this chapter, we first introduce quasi‐2D perovskite materials' structural characteristics and stability advantages. Then, we focus on the carrier transport dynamics of quasi‐2D perovskite and summarize some methods to improve its efficiency. Subsequently, we sum up the important role of 2D/3D structure in realizing efficient and stable photovoltaic devices. Finally, we give an outlook for the future …

Serious performance decline arose for perovskite light-emitting diodes (PeLEDs) once the active area was enlarged. Here we investigate the failure mechanism of the widespread active film fabrication method; and ascribe severe phase-segregation to be the reason. We thereby introduce L-Norvaline to construct a COO−-coordinated intermediate phase with low formation enthalpy. The new intermediate phase changes the crystallization pathway, thereby suppressing the phase-segregation. Accordingly, high-quality large-area quasi-2D films with desirable properties are obtained. Based on this, we further rationally adjusted films’ recombination kinetics. We reported a series of highly-efficient green quasi-2D PeLEDs with active areas of 9.0 cm2. The peak EQE of 16.4% is achieved in <n > = 3, represent the most efficient large-area PeLEDs yet. Meanwhile, high brightness device with luminance up to 9.1 × 104 …

Quasi-two-dimensional (quasi-2D) perovskites have attracted extraordinary attention due to their superior semiconducting properties and have emerged as one of the most promising materials for next-generation light-emitting diodes (LEDs). The outstanding optical properties originate from their structural characteristics. In particular, the inherent quantum-well structure endows them with a large exciton binding energy due to the strong dielectric- and quantum-confinement effects; the corresponding energy transfer among different n-value species thus results in high photoluminescence quantum yields (PLQYs), particularly at low excitation intensities. The review herein presents an overview of the inherent properties of quasi-2D perovskite materials, the corresponding energy transfer and spectral tunability methodologies for thin films, as well as their application in high-performance LEDs. We then summarize the …

Aqueous zinc‐ion batteries (ZIBs) are considered to be a promising candidate for flexible energy storage devices due to their high safety and low cost. However, the scalable assembly of flexible ZIBs is still a challenge. Here, a scalable assembly strategy is developed to fabricate flexible ZIBs with an ultrathin all‐in‐one structure by combining blade coating with a rolling assembly process. Such a unique all‐in‐one integrated structure can effectively avoid the relative displacement or detachment between neighboring components to ensure continuous and effective ion‐ and/or loading‐transfer capacity under external deformation, resulting in excellent structural and electrochemical stability. Furthermore, the ultrathin all‐in‐one ZIBs can be tailored and edited controllably into desired shapes and structures, further extending their editable, stretchable, and shape‐customized functions. In addition, the ultrathin all‐in …

Hybrid perovskite solar cell (PSC) has attracted extensive research interest due to its rapid increase in efficiency, regarding as one of the most promising candidates for the next-generation photovoltaic technology. The certified power conversion efficiency of the devices based on formamidinium lead iodide (FAPbI3) perovskite has reached 25.5%, approaching the record of monocrystalline silicon solar cells. Unfortunately, the black α-phase FAPbI3 materials can spontaneously transform to non-optically active δ-phase at room temperature, which greatly hinder their photovoltaic application. In order to overcome this problem, various strategies, especially introducing methylammonium (MA+), caesium (Cs+) and bromide (Br-) ions into the materials, have been widely adopted. However, MA+ can largely reduce the thermal stability of the materials. Furthermore, the introduction of Br- can enlarge the materials’ bandgap …

Mixed-halide perovskite provides band-gap tunability, which is essential for tandem solar cell application. However, ion migration inducing phase segregation seriously affects the device's long-term operational stability. The issue thus represents an important challenge for the whole perovskite community and urgently needs effective solutions. We showcase here for the first time that a strong chemical interaction, a halogen-halogen bond, is introduced at the phase interface to suppress the ion migration by increasing the corresponding activation energy. Various characterizations have proved that halogen-halogen bonds form between 2D and 3D phases, which do suppress the halide segregation. As expected, the encapsulated device retains 90% of initial power conversion efficiency (PCE) after maximum power point (MPP) tracking for ∼500 h under continuous simulated 1-sun illumination (AM 1.5) in ambient …

Electron transport layers (ETLs) based on tin oxide (SnO2) get wide attention in planar perovskite solar cells (PSCs), with the merits of high electron mobility and low-temperature fabrication. However, the poor electron extraction ability of SnO2 seriously deteriorates the performance of devices. Herein, we report an optimized strategy for SnO2 films to enhance the carrier transport. The dense and pinhole free ETL films with Li doping are developed by chemical bath deposition. Li-doped SnO2 shows better energy band alignment between ETLs and perovskite layers, which facilitates the electron extraction and reduces recombination loss. On the basis of the above improved performances, the PSCs with Li-doped SnO2 have achieved an improved power conversion efficiency (PCE) over 22%. The unencapsulated devices show excellent stability, and the PCE exhibits almost no change after 800 h storage.

Organic–inorganic hybrid lead‐halide perovskite materials (ABX3) have attracted widespread attention in the field of photovoltaics owing to their impressive optical and electrical properties. However, obstacles still exist in the commercialization of perovskite photovoltaics, such as poor stability, hysteresis, and human toxicity. A‐site cation engineering is considered to be a powerful tool to tune perovskite structures and the resulting optoelectronic properties. Based on the selection and combination of A‐site cations, three types of perovskite structures, i.e., 3D perovskite, reduced‐dimensional (2D/quasi‐2D) perovskite, and 2D/3D hybrid perovskite can be formed. Herein, the remarkable breakthroughs resulting from these three perovskite structures are summarized, and their corresponding properties and characteristics, as well as their intrinsic disadvantages, are highlighted. By summarizing recent research progress …