JIALINGBO

Polar molecules with different degrees of dipole moments are proposed to terminate the perovskite structure by forming the dipole interlayer. The introduction of a dipole interlayer not only adjusts the energy level alignment, but also the functional groups present can coordinate with the Pb atoms at the surface of the perovskite film to reduce the defect content and facilitate the carrier extraction.

Abstract

The ionic nature of the organic-inorganic hybrid perovskite material is prone to react with different functional groups. Here, a series of polar molecules with permanent dipole moments are designed to modify the perovskite surface termination. It is observed that proper interfacial design can significantly reduce trap state density for effective charge transfer. The energy level of the substrate can be adjusted by the magnitude and direction of the dipole moment. As a result, a high 24.54% photo-electric conversion efficiency is reached by introducing pentafluoride benzene moieties with carboxylic functional groups. In addition, the humidity and heat stability of the perovskite device is obviously improved. This work demonstrates the importance of chemical interactions at perovskite termination and paves the way for further enhancing the performance of perovskite solar cells.

Surface passivation can reduce defects in the perovskite film. It is shown that exposing a preannealed perovskite film to a mild ethylenediamine vapor environment lowers the defect density by four times, enhances radiative yield and improves the device performance. The impact of these defects on the operational stability is investigated by tracking the hysteresis index.

Defects present at the surface or within the bulk of halide perovskites act as a barrier to charge transfer/transport, induce nonradiative recombination thereby limit open-circuit voltage (V _OC), and accelerate degradation in the perovskite solar cells (PSCs). Passivation of these defects at surfaces, interfaces, and grain boundaries to suppress the charge recombination is therefore imperative to improving photovoltaic performance in the PSCs. Herein, a facile posttreatment of perovskite surface by ethylenediamine (EDA) via mixed solvent vapor annealing method is reported. The results show that only a trace amount of EDA causes significant suppression of nonradiative recombination leading to over 100 mV increased V _OC and ≈22% improvement in power conversion efficiency (PCE) of the inverted PSCs. The key reasons for this improvement are an upward shift in the Fermi energy level, reduced lattice strain and Urbach energy, and reduction in nonradiative recombination upon EDA passivation. These lead to a PCE exceeding 20% up from 16% for a nonpassivated film. The unencapsulated EDA-modified PSCs also demonstrate an improved shelf-life and retain 87% of the initial PCE after 850 h.

Nature Communications, Published online: 15 February 2023; doi:10.1038/s41467-023-36229-1

Nature Energy, Published online: 09 February 2023; doi:10.1038/s41560-023-01205-y

Vacuum evaporation of lead iodide and solution processing of organic ammonium halide are combined to produce large-area homogeneous perovskite films with high reproducibility. The resulting PSCs achieve a power conversion efficiency (PCE) of 24.0% (certified PCE 23.7%) on large area (1 cm²) under AM 1.5G illumination, which is currently the highest PCE for large area perovskite photovoltaics.

Abstract

Organic–inorganic hybrid perovskites exhibit outstanding performances in perovskite solar cells (PSCs). However, the complex solution chemistry of perovskites precursors renders it difficult to prepare large-area devices in a reproducible way, which is a prerequisite for the technology to make an impact beyond lab scale. Vacuum processing, instead, is an established technology for large-scale coating of thin films. However, with respect to the hybrid perovskites it is highly challenging due to the high vapor pressure of the organic ammonium halide. In this work, vacuum evaporation of lead iodide and solution processing of organic ammonium halide is combined to produce large-area homogeneous perovskite films with large grains in a highly reproducible way. The resulting PSCs achieve a power conversion efficiency (PCE) of 24.3% (certified 23.9%) on small area (0.10 cm²), 24.0% (certified 23.7%) on large area (1 cm²) and 20.0% for minimodule (16 cm²), and maintain 90% of its initial efficiency after 1000 h 1-sun operation. The vacuum evaporation prevents advert environmental effects on lead halide formation and guarantees a reproducible fabrication of high-quality large-area perovskite films, which opens a promising way for large-scale fabrication of perovskite optoelectronics.

Publication date: May 2023

Source: Nano Energy, Volume 109

Author(s): Luigi Angelo Castriotta, Emanuele Calabrò, Francesco Di Giacomo, Sathy Harshavardhan Reddy, Daimiota Takhellambam, Barbara Paci, Amanda Generosi, Luca Serenelli, Francesca Menchini, Luca Martini, Mario Tucci, Aldo Di Carlo

Publication date: April 2023

Source: Nano Energy, Volume 108

Author(s): Yue Ma, Qizhen Song, Xiaoyan Yang, Huachao Zai, Guizhou Yuan, Wentao Zhou, Yihua Chen, Fengtao Pei, Jiaqian Kang, Hao Wang, Tinglu Song, Xueyun Wang, Huanping Zhou, Yujing Li, Yang Bai, Qi Chen

Herein, the factors affecting the stability of perovskite solar cells (PSCs) are analyzed and the encapsulations are divided into inner encapsulation and outer encapsulation based on the encapsulation materials' location and function. Then, the classification and application of encapsulation materials are systematically summarized. In addition, the encapsulation techniques, the characterization technologies, and stability tests of encapsulated PSCs are also proposed.

The poor stability hampers the commercialization of perovskite solar cells (PSCs). Many methods have recently been reported to enhance their stability, among which encapsulation is one of the most effective methods to improve the stability of PSCs. Herein, a summary of the factors influencing the stability of PSCs is provided and the commonly used encapsulation technologies and different types of encapsulation materials in detail are introduced. Then, the characterization technologies of encapsulation and stability tests of encapsulated PSCs are proposed. Finally, current issues and chances for encapsulating material development are considered.

Cost-effective self-assembled molecules bearing anchoring groups are developed and applied as hole transporting layer in p–i–n perovskite solar cells. The donor–acceptor type self-assembled molecule has strong interactions with indium doped tin oxide substrate and perovskite, resulting in a power conversion efficiency of over 23% and a lifetime of over 2000 h at 80% efficiency (T₈₀) under maximum power point tracking.

Abstract

The self-assembled hole transporting molecules (SAHTMs) bearing anchoring groups have been established as the hole transporting layers (HTLs) for highly efficient p–i–n perovskite solar cells (PSCs), yet their stability and engineering at the molecular level remain challenging. A topological design of highly anisotropic aligned SAHTM-based HTLs for operationally stable PSCs that exhibit exceptional solar-to-electric power conversion efficiencies (PCEs) is demonstrated. The judiciously designed multifunctional self-assembled molecules comprise the donor–acceptor subunit for hole transporting and the phosphonic acid group for anchoring, realizing face-on π-stacking parallel to the transparent conductive oxide substrate. The high affinity of SAHTMs to the multi-crystalline perovskite thin film benefits passivating the perovskite buried interface, strengthening interfacial contact while facilitating interfacial hole transfer. Consequently, highly efficient p–i–n PSC devices are obtained with a champion PCE of 23.24% and outstanding operational stability toward various environmental factors including long-term full sunlight soaking at evaluated temperatures. Perovskite solar modules with a champion efficiency approaching 20% are also fabricated for an active device area above 17 cm².

A reactive surface modification strategy exploiting the pyrolysis of urea is developed to deal with the nickel oxide hole selective contact. The surface reactions reduce high-valence nickel states and hydroxyl groups on the NiO _x surface, enabling a high-quality NiO _x /perovskite heterointerface. The NiO _x -based perovskite solar cells achieve an impressive efficiency of 23.61% and a fill factor of over 86%.

Abstract

The poor interface quality between nickel oxide (NiO _x ) and halide perovskites limits the performance and stability of NiO _x -based perovskite solar cells (PSCs). Here a reactive surface modification approach based on the in situ decomposition of urea on the NiO _x surface is reported. The pyrolysis of urea can reduce the high-valence state of nickel and replace the adsorbed hydroxyl group with isocyanate. Combining theoretical and experimental analyses, the treated NiO _x films present suppressed surface states and improved transport energy level alignment with the halide perovskite absorber. With this strategy, NiO _x -based PSCs achieve a champion power conversion efficiency (PCE) of 23.61% and a fill factor of over 86%. The device's efficiency remains above 90% after 2000 h of thermal aging at 85 °C. Furthermore, perovskite solar modules achieve PCE values of 18.97% and 17.18% for areas of 16 and 196 cm², respectively.

This work demonstrates an universal chloride redistribution and passivation induced by post-treatment. The chloride enrichment on the surface can improve charge transport and the passivation can reduce the recombination. When cyclohexylmethylammonium iodide (CHMAI) post-treated perovskite film, the Cl/I ratio on surface increased from 0.037 to 0.439, which leveraged their roles in charge transport/recombination. Finally, CHMAI perovskite solar cells deliver a champion power conversion efficiency of 24.42%.

Abstract

Post-treatment is an essential passivation step for the state-of-the-art perovskite solar cells (PSCs) but the additional role is not yet exploited. In this work, perovskite film is fabricated under ambient air with wide humidity window and identify that chloride redistribution induced by post-treatment plays an important role in high performance. The chlorine/iodine ratio on the perovskite surface increases from 0.037 to 0.439 after cyclohexylmethylammonium iodide (CHMAI) treatment and the PSCs deliver a champion power conversion efficiency (PCE) of 24.42% (certificated 23.60%). The maximum external quantum efficiency of electroluminescence (EQE_EL) reaches to 10.84% with a radiance of 170 W sr⁻¹ m⁻², forming the reciprocity relation between EQE_EL and nonradiative open-circuit voltage loss (86.0 mV). After thermal annealing, 2D component of perovskite will increase while chloride decline, leading to improved photovoltage but reduced fill factor. Hence, it distinguishes that chloride enrichment can improve charge transport/recombination simultaneously and 2D passivation can suppress the nonradiative recombination. Moreover, CHMAI can leverage their roles in charge transport/recombination for better performance than phenylethylammonium iodide (Cl/I = 0.114, PCE = 23.32%), due to the stronger binding energy of Cl⁻. This work provides the insight that the chloride fixation can improve the photovoltaic performance.

This study suggests that the general use of phenethylamine-based interlayers results in the degradation of perovskite. Focusing on these degradation mechanisms, poly(methyl methacrylate) (PMMA) is a breakthrough in preventing direct contact between perovskite (PVK) and phenethylamine halides (PEAX). The PMMA/PEAX double interlayer is effective for both stability and efficiency of the perovskite solar cell, and heat treatment (PMMA/H-PEABr) maximizes overall performance.

Phenethylamine (PEA) halides (X) coated on perovskite (PVK) films are widely known as passivating layers, resulting in high performance in perovskite solar cells (PSCs). However, critical stability issues associated with phenethylamine halides (PEAX) in PSCs are observed, especially with Spiro-OMeTAD, which prevented its practical use. Here, the mechanism by which PEAX negatively affects PSCs is reported. In addition, a method is devised to overcome the stability issue by employing poly(methyl methacrylate) (PMMA) at the PVK/PEABr interface to form dual PMMA/PEABr interlayers. Contrary to the general use of PEABr, the indirect contact of PEABr with PVK films by PMMA resulted in superior power conversion efficiencies (PCEs) and enhanced stability resulting from the retention of dipole moments even under aging. Further, effective methods of maximizing and retaining the dipole effect by heating PMMA/PEAX, as opposed to PSCs incorporating PEAX without PMMA being negatively affected by heat are exploited. The resulting PSCs with PMMA/heated PEABr exhibit a PCE of 21.63%, and retain 95% of their original performance a month after fabrication.

Publication date: 15 February 2023

Source: Joule, Volume 7, Issue 2

Author(s): Jung Hwan Lee, SunJe Lee, Taehee Kim, Hyungju Ahn, Gyu Yong Jang, Kwang Hee Kim, Yoon Jun Cho, Kan Zhang, Ji-Sang Park, Jong Hyeok Park

The spatial and temporal evolution in the recombination of back-contact perovskite solar cells is studied using intensity-dependent photoluminescence. Maps of the photoluminescence intensity and ideality factor resemble the periodic structure of the back-contact electrodes and exhibit interesting transient behavior. Adding a mesoporous TiO₂ layer drastically reduces recombination and lowers the ideality factor, improving the open-circuit voltage (V _OC) by 120 mV.

Abstract

The efficiency of back-contact perovskite solar cells has steadily increased over the past few years and now exceeds 11%, with interest in these devices shifting from proof-of-concept to viable technology. In order to make further improvements in the efficiency of these devices it is necessary to understand the cause of the low fill factor, low open-circuit voltage (V _OC), and severe hysteresis. Here a time-dependent Suns-V _oc and Suns-photoluminescence (PL) analysis are performed to monitor the transient ideality factor spatially. Two sets of quasi-interdigitated back-contact perovskite solar cells are studied; cells with and without a mesoporous TiO₂ layer. Maps of the PL intensity and ideality factor resemble the periodic structure of the back-contact electrodes and the transient behavior exhibit distinct features such as a temporary variation in the periodicity of the modulation, spatial phase shifting, and phase offsets. It is shown that the presence of the mesoporous layer greatly reduces recombination, increasing the V _OC by 0.12 V. Coupled 2D time-dependent drift-diffusion simulations allow the experimental results to be modeled, and replicate the key features observed experimentally. They reveal that non-uniform ion distribution along the transport layer interfaces can drastically alter the PL intensity and ideality factor throughout the device.

An all-solution-processed perovskite light-emitting diodes based on core/shell ZnO/ZnS nanoparticles as electron transport layer are reported. The resulting device realizes a high peak brightness of 32 400 cd m⁻², peak external quantum efficiency of 10.3%, and 20-fold extended longevity as compared to devices utilizing ZnO nanoparticles.

Abstract

Solution-processed perovskite-based light-emitting diodes (PeLEDs) are promising candidates for low-cost, large-area displays, while severe deterioration of the perovskite light-emitting layer occurs during deposition of electron transport layers from solution in an issue. Herein, core/shell ZnO/ZnS nanoparticles as a solution-processed electron transport layer in PeLED based on quasi-2D PEA₂Cs_n−1Pb_nBr_3n+1 (PEA = phenylethylammonium) perovskite are employed. The deposition of ZnS shell mitigates trap states on ZnO core by anchoring sulfur to oxygen vacancies, and at the same time removes residual hydroxyl groups, which helps to suppress the interfacial trap-assisted non-radiative recombination and the deprotonation reaction between the perovskite layer and ZnO. The core/shell ZnO/ZnS nanoparticles show comparably high electron mobility to pristine ZnO nanoparticles, combined with the reduced energy barrier between the electron transport layer and the perovskite layer, improving the charge injection balance in PeLEDs. As a result, the optimized PeLEDs employing core/shell ZnO/ZnS nanoparticles as a solution-processed electron transport layer exhibit high peak luminance reaching 32 400 cd m⁻², external quantum efficiency of 10.3%, and 20-fold extended longevity as compared to the devices utilizing ZnO nanoparticles, which represents one of the highest overall performances for solution-processed PeLEDs.

Tandem solar cells with a simple silicon heterojunction bottom solar cell design and a p–i–n perovskite top solar cell are optimized to yield current matching with a high short-circuit current density of 19.6 mA cm⁻². Experimental measures to improve the tandem device are guided by optical simulation and in-depth spectral characterization.

Perovskite silicon tandem solar cells can overcome the efficiency limit of silicon single-junction solar cells. In two-terminal perovskite silicon tandem solar cells, current matching of subcells is an important requirement. Herein, a current-matched tandem solar cell using a planar front/ rear side-textured silicon heterojunction bottom solar cell with a p–i–n perovskite top solar cell that yields a high certified short-circuit current density of 19.6 mA cm⁻² is reported. Measures taken to improve the device are guided by optical simulation and a derived optical roadmap toward maximized tandem current density. To realize current matching of the two subcells, variation of the perovskite bandgap from ≈1.68 to 1.64 eV and thickness is investigated. Spectrometric characterization, in which current–voltage curves of tandem devices are recorded at systematically varied spectral irradiance conditions, is applied to determine the current matching point. In addition, remaining device limitations such as nonradiative recombination at the perovskite's interfaces are analyzed. Replacing the hole transport layer PTAA by 2PACz results in an overall certified power conversion efficiency of up to 26.8%. Precise simulation based on the device structure is essential as it provides efficient paths toward improving the device efficiency.

Processing perovskite solar cells (PSCs) by industry-compatible methods is a cornerstone requirement for its commercial massification. This work reaches a stable cross-web flow in a slot-die head, ultimately leading to more uniform and repeatable large-area perovskite layers, through computer fluid dynamics (CFD) simulations, experimental validation, and calculation of industrial uniformity parameters.

Large-scale manufacturing of perovskite solar cells (PSCs) requires the deposition of homogeneous and defect-free perovskite films on large-area substrates. Up to now, the knowledge developed for industrial slot-die processing has not been fully transferred to the perovskite photovoltaic community. Here, the deposition of uniform perovskite layers by slot-die coating (SDC). Computer fluid dynamics (CFD) simulations, experimental validation, and calculation of industrial uniformity parameters are demonstrated, which enabled to establish processing conditions for SDC of perovskite ink. This approach allowed for obtaining stable cross-web flow in the slot-die head resulting in the formation of a stable coating bead yielding uniform perovskite films. The best processing parameters are used for the fabrication of slot-die-coated PSCs, which showed a more homogeneous spatial distribution of photovoltaic parameters compared to their spin-coated counterparts. Better reproducibility observed in device performance is a step forward toward the commercialization of perovskite photovoltaic technology. For the first time, the industrial approach used for the optimization of slot-die coating is applied for the processing of perovskite inks that have special conditions such as low viscosity and in situ crystallization on the substrate.

Publication date: April 2023

Source: Nano Energy, Volume 108

Author(s): Jindan Zhang, Chi Li, Mengqi Zhu, Junming Qiu, Yisi Yang, Lu Li, Shicheng Tang, Zhenghong Li, Ziwen Mao, Zhibing Cheng, Shengchang Xiang, Xiaoliang Zhang, Zhangjing Zhang