Chen Weijie

In this study, inorganic CsPbBr₃ perovskite films are prepared using a two-step spin-coating method, and turmeric and carotene dyes are introduced into CsPbBr₃ films. These dyes enhance light absorption and carrier transport by increasing CsPbBr₃ crystal size and reducing defects. The turmeric and carotene additives elevate the efficiency of the solar cell devices from 5.35% to 9.78% and 7.81%, respectively.

Inorganic perovskite solar cells have attracted considerable interest for their thermal stability. In this study, turmeric and carotene natural dyes as additives for refining CsPbBr₃ film crystal structure are explored. These dyes enhance light absorption and carrier transport by increasing CsPbBr₃ crystal size and reducing defects. Capitalizing on the dyes’ light-absorbing nature and their impact on device energy levels, turmeric and carotene additives elevate efficiency from 5.35% to 9.78% and 7.81%, respectively. Remarkably, device stability extends 90 days without encapsulation. In this work, an eco-friendly, economical method to optimize perovskite crystallization is introduced and optoelectronic properties in inorganic perovskite solar cells are enhanced.

Compared to labor-intensive trial-and-error approaches, machine learning (ML) is effective in designing stable and effective perovskites and optimizing perovskite solar cells. In this review, the basic procedure of ML and latest progress in applying ML to materials development and solar cell fabrication are reviewed. The challenges and suggestions on the future development of ML are also discussed.

Perovskite solar cells (PSC) are a potential candidate for next-generation photovoltaic technology. Despite the significant advancements in the field of PSCs, the ongoing development of stable and efficient metal halide perovskite materials, along with their successful integration into photovoltaic applications, remains challenges. These challenges originate from the diverse range of device structures and perovskite compositions, requiring meticulous consideration and optimization. Traditional trial-and-error methods are characterized by their sluggishness and labor-intensive nature. Recently, the emergence of extensive datasets and advancements in computer hardware have facilitated the utilization of machine learning (ML) across multiple domains, including in various fields for material discovery and experimental optimization. Herein, the fundamental procedure of ML is briefly introduced, and latest progress of ML in the materials development and solar cell fabrication is comprehensively reviewed. The utilization of ML in PSCs at all stages of design can be categorized into four main areas: screening perovskite material, fabrication process optimization, device structure optimization, and understanding mechanism. The challenges and outlooks on the future development of ML are finally discussed. It is highly expected that this review can offer valuable guidance for the design and development of highly efficient and stable PSCs.

A hole transport layer material (BDT-C8-3O) for perovskite solar cells is designed, introducing an asymmetric polar oligo(ethylene glycol) side chain. It is capable of achieving high crystallinity even when processed from green solvents. The n-i-p perovskite solar cells based on chlorobenzene- or 3-methylcyclohexanone-processed BDT-C8-3O without dopant delivered world-record power conversion efficiencies of 24.11 % (certified of 23.82 %) and 23.53 %, respectively. The corresponding scaled modules (15.64 cm²) also deliver high PCEs over 20 %.

Abstract

The use of dopant-free hole transport layers (HTLs) is critical in stabilizing n-i-p perovskite solar cells (pero-SCs). However, these HTL materials are often processed with toxic solvents, which is not ideal for industrial production. Upon substituting them with green solvents, a trade-off emerges between maintaining the high crystallinity of the HTL materials and ensuring high solubility in the new solvents. In this paper, we designed a novel, linear, organic small molecule, BDT-C8-3O, by introducing an asymmetric polar oligo(ethylene glycol) side chain. This method not only overcomes the solubility limitations in green solvents but also enables stacking the conjugated main chains in two patterns, which further enhances crystallinity and hole mobility. As a result, the n-i-p pero-SCs based on chlorobenzene- or green (natural compound) solvent 3-methylcyclohexanone-processed BDT-C8-3O HTL that without any dopant delivered world-recorded power conversion efficiencies of 24.11 % (certified of 23.82 %) and 23.53 %, respectively. The devices also demonstrated remarkable operational and high-temperature stabilities, maintaining over 84 % and 79.5 % of their initial efficiency for 2000 h, respectively. Encouragingly, dopant-free BDT-C8-3O HTL exhibits significant advantages in large-area fabrication, achieving state-of-the-art PCEs exceeding 20 % for 5×5 cm² modules (active area: 15.64 cm²), even when processed using green solvents.

The accession of potassium pentaminodifluorobenzoate (KAFA) effectively passivates the SnO₂/perovskite interface and grain boundary defects, thereby enhancing carrier extraction and inhibiting carrier recombination. Meanwhile, the modification of KAFA improves the film quality of SnO₂ and perovskite and promotes the stability of the device. This increases the power conversion efficiency of the device from 20.36% to 22.46%.

Perovskite solar cells have rapidly developed into the standard representative of the third generation of photovoltaic power generation due to their low energy consumption and low cost. This device faces many challenges in achieving higher efficiency and better long-term stability. The core issue is the passivation of various defects and appropriate energy-level matching. Herein, the use of potassium pentaminodifluorobenzoate (KAFA) not only improves the light transmittance of SnO₂/ITO, but also passivates the interface defects of SnO₂/perovskite by introducing amino, carboxyl, fluorine, and potassium ions. This allows the device to form a suitable energy-level arrangement, thereby greatly improving the performance of perovskite solar cells. Compared with 20.36% of the pristine device, the KAFA-SnO₂-based device achieves a champion power conversion efficiency of 22.46%, with an increase in short-circuit current from 23.94 to 24.78 mA cm⁻² and open-circuit voltage from 1.149 to 1.169 V. After 120 h of continuous illumination with standard sunlight under N₂ atmosphere, its initial efficiency is still as high as 88.8%, showing excellent stability.

“Perovskite/carbon” interface remains as a bottleneck for carbon-electrode basing perovskite solar cells, especially for hole-conductor-free devices. Here an “in-situ healing” strategy is proposed by simply doping OAI in the carbon paste, which helps to effectively reduce defects and strengthen contact at the interface, and hence elevates the device efficiency from ≈13% to >19%, with 85% RH-moisture stability in addition.

Abstract

“Perovskite/carbon” interface is a bottle-neck for hole-conductor-free, carbon-electrode basing perovskite solar cells due to the energy mismatch and concentrated defects. In this article, in-situ healing strategy is proposed by doping octylammonium iodide into carbon paste that used to prepare carbon-electrode on perovskite layer. This strategy is found to strengthen interfacial contact and reduce interfacial defects on one hand, and slightly elevate the work function of the carbon-electrode on other hand. Due to this effect, charge extraction is accelerated, while recombination is obviously reduced. Accordingly, power conversion efficiency of the hole-conductor-free, planar perovskite solar cells is upgraded by ≈50%, or from 11.65 (± 1.59) % to 17.97 (± 0.32) % (AM1.5G, 100 mW cm⁻²). The optimized device shows efficiency of 19.42% and open-circuit voltage of 1.11 V. Meanwhile, moisture-stability is tested by keeping the unsealed devices in closed chamber with relative humidity of 85%. The “in-situ healing” strategy helps to obtain T₈₀ time of >450 h for the carbon-electrode basing devices, which is four times of the reference ones. Thus, a kind of “internal encapsulation effect” has also been reached. The “in situ healing” strategy facilitates the fabrication of efficient and stable hole-conductor-free devices basing on carbon-electrode.

Simple and low cost vanadyl oxalate (VOC₂O₄) has been identified as efficient hole transporting layer (HTL) in organic solar cells to facilitate high efficiency and stability. The robust VOC₂O₄ HTL can be fabricated with wide conditions, especially annealing at 200 °C and treated with UV-ozone affording a top efficiency of 18.94% with a fill factor of 80% in binary OSCs.

Abstract

Organic solar cells (OSCs) with the conventional configuration usually use polyethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) as the hole-transporting layer (HTL); however, its acidity tends to affect the performance and long-term stability of the devices. Therefore, replacing PEDOT:PSS with other more stable HTLs is essential for realizing the practical applications of OSCs. To achieve this goal, a simple and low-cost vanadyl oxalate (VOC₂O₄) is identified as a HTL to facilitate high power conversion efficiencies (PCEs), good stability, and high thickness tolerance to be achieved in OSCs. The VOC₂O₄ thin film can be easily prepared by spin-coating from its aqueous solution onto ITO/glass substrate and thermally annealed at 100 °C to exhibit high transmittance, conductivity, and work function. It can be applied as a robust HTL with wide processing conditions, especially after being heated at 200 °C and treated with UV-ozone (UVO) to afford a very high PCE of 18.94% in OSCs. This value is among the highest PCEs obtained for binary OSCs. In addition, the derived OSCs exhibit high thickness tolerance and better stability than those based on PEDOT:PSS as HTL. These results reveal that VOC₂O₄ is an excellent HTL for OSCs, having great potential for large-area device applications.

In passivating perovskite defects it is shown that the F group can interact with the passivation groups of the additives, leading to different abilities to passivate defects rather than only introducing additional interactions between F and Pb²⁺ as previously thought. The efficiencies of perovskite solar cells and modules made with the fluorinated passivators reach 24.70 % (0.09 cm²) and 21.13 % (14.0 cm²), respectively, with long-term stability.

Abstract

Introducing fluorine (F) groups into a passivator plays an important role in enhancing the defect passivation effect for the perovskite film, which is usually attributed to the direct interaction of F and defect states. However, the interaction between electronegative F and electron-rich passivation groups in the same molecule, which may influence the passivation effect, is ignored. We herein report that such interactions can vary the electron cloud distribution around the passivation groups and thus changing their coordination with defect sites. By comparing two fluorinated molecules, heptafluorobutylamine (HFBM) and heptafluorobutyric acid (HFBA), we find that the F/−NH₂ interaction in HFBM is stronger than the F/−COOH one in HFBA, inducing weaker passivation ability of HFBM than HFBA. Accordingly, HFBA-based perovskite solar cells (PSCs) provide an efficiency of 24.70 % with excellent long-term stability. Moreover, the efficiency of a large-area perovskite module (14.0 cm²) based on HFBA reaches 21.13 %. Our work offers an insight into understanding an unaware role of the F group in impacting the passivation effect for the perovskite film.

Publication date: 18 October 2023

Source: Joule, Volume 7, Issue 10

Author(s): Caixuan Wang, Xiaoming Ma, Yi-fan Shen, Dan Deng, Hao Zhang, Tong Wang, Jianqi Zhang, Jing Li, Rui Wang, Lili Zhang, Qian Cheng, Ziqi Zhang, Huiqiong Zhou, Chenyang Tian, Zhixiang Wei

A chemical anticorrosion strategy is proposed to inhibit Ag electrode corrosion in inverted perovskite solar cells through introducing 2-mercaptobenzothiazole (MBT) inhibitor. MBT can bond on Ag surface to inhibit Ag corrosion. Resulting devices exhibit >23% efficiency with good stability, retaining >90% of initial efficiency whether after N₂ storage for 3800 h or 85 °C aging for 900 h.

Abstract

Ag electrode is widely used in inverted perovskite solar cells (PSCs), but its easy reaction and corrosive nature with perovskite always induces severe stability issue. Here, from typical theory of metal anticorrosion, a chemical anticorrosion approach for Ag electrode in inverted PSCs through introducing 2-mercaptobenzothiazole (MBT) as a corrosion inhibitor is reported. MBT can strongly bond to Ag and form a compact [MBT-Ag] chain on Ag surface owing to its N atom in thiazolyl ring and exocyclic thiol groups. As a result, Ag anticorrosion ability is greatly enhanced by increasing the corrosion potential and decreasing the corrosion current, thus effectively inhibiting possible chemical reaction and corrosion between perovskite and Ag electrodes. PSCs containing MBT/Ag exhibit high efficiency of over 23% with good stability, retaining 95 ± 4.1% of initial efficiency after storage for 3800 h in glovebox. Importantly, resulting PSCs also show excellent thermal stability, maintaining 90 ± 1.8% of initial efficiency after aging for 900 h at 85 °C.

Nature Photonics, Published online: 21 September 2023; doi:10.1038/s41566-023-01287-w

Ternary organic solar cells (OSCs) with high thickness tolerance are realized via introducing an oligomer DY-TF as third component. Upon addition of DY-TF, the crystallinity of the host blend is improved and a well-defined morphology with vertical phase separation is formed, yielding an efficiency of 18.23%, which represents the highest efficiency value for 300 nm-thick OSCs thus far.

Abstract

The development of high-efficiency thickness-insensitive organic solar cells (OSCs) is crucially important for the mass production of solar panels. However, increasing the active layer thickness usually induces a substantial loss in efficiency. Herein, a ternary strategy in which an oligomer DY-TF is incorporated into PM6:L8-BO system as a guest component is adopted to break this dilemma. The S···F intramolecular noncovalent interactions in the backbone endow DY-TF with a high planarity. Upon the addition of DY-TF, the crystallinity of the blend is effectively improved, leading to increased charge carrier mobility, which is highly desirable in the fabrication of thick-film devices. As a result, thin-film PM6:L8-BO:DY-TF-based device (110 nm) shows a power conversion efficiency (PCE) of 19.13%. Impressively, when the active layer thickness increases to 300 nm, an efficiency of 18.23% (certified as 17.8%) is achieved, representing the highest efficiency reported for 300 nm thick OSCs thus far. Additionally, blade-coated thick device (300 nm) delivers a promising PCE of 17.38%. This work brings new insights into the construction of efficient OSCs with high thickness tolerance, showing great potential for roll-to-roll printing of large-area solar cells.

Photogenerated I₂ in the mixed I-Br perovskite induces I-rich phase formation through a chemical chain reaction. The Br⁻ binding strength in the perovskite regulates the chemical chain reaction and thus the I-rich phase formation. This study demonstrates the increasing of Br-binding strength and eliminating of defects leading to I₂ photogeneration in the lattice to stabilize the mixed I-Br perovskite.

Abstract

Bandgap tunability of lead mixed halide perovskites (LMHPs) is a crucial characteristic for versatile optoelectronic applications. Nevertheless, LMHPs show the formation of iodide-rich (I-rich) phase under illumination, which destabilizes the semiconductor bandgap and impedes their exploitation. Here, it is shown that how I₂, photogenerated upon charge carrier trapping at iodine interstitials in LMHPs, can promote the formation of I-rich phase. I₂ can react with bromide (Br⁻) in the perovskite to form a trihalide ion I₂Br⁻ (I^δ−-I^δ+-Br^δ−), whose negatively charged iodide (I^δ−) can further exchange with another lattice Br⁻ to form the I-rich phase. Importantly, it is observed that the effectiveness of the process is dependent on the overall stability of the crystalline perovskite structure. Therefore, the bandgap instability in LMHPs is governed by two factors, i.e., the density of native defects leading to I₂ production and the Br⁻ binding strength within the crystalline unit. Eventually, this study provides rules for the design of chemical composition in LMHPs to reach their full potential for optoelectronic devices.

A facile solvent-engineering strategy is developed to form a stable intermediate perovskite complex during the fabrication stage, resulting in a high efficiency of 35.99% under indoor illumination conditions by suppressing intrinsic defects, prolonging charge carrier lifetimes, and reducing non-radiative charge recombination in the perovskite films.

Abstract

Lead halide perovskite solar cells have been emerging as very promising candidates for applications in indoor photovoltaics. To maximize their indoor performance, it is of critical importance to suppress intrinsic defects of the perovskite active layer. Herein, a facile solvent-engineering strategy is developed for effective suppression of both surface and bulk defects in lead halide perovskite indoor solar cells, leading to a high efficiency of 35.99% under the indoor illumination of 1000 lux Cool-white light-emitting diodes. Replacing dimethylformamide (DMF) with N-methyl-2-pyrrolidone (NMP) in the perovskite precursor solvent significantly passivates the intrinsic defects within the thus-prepared perovskite films, prolongs the charge carrier lifetimes and reduces non-radiative charge recombination of the devices. Compared to the DMF, the much higher interaction energy between NMP and formamidinium iodide/lead halide contributes to the markedly improved quality of the perovskite thin films with reduced interfacial halide deficiency and non-radiative charge recombination, which in turn enhances the device performance. This work paves the way for developing efficient indoor perovskite solar cells for the increasing demand for power supplies of Internet-of-Things devices.

A moisture-induced secondary crystal growth strategy is proposed to enhance the crystalline quality of thick perovskite films. The secondary growth results in improved crystal quality of the perovskite film and also optimizes energy level alignment. The efficiency of hole transport layer-free carbon-based perovskite solar cells is boosted to 19.52%.

Abstract

Hole transport layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) show promising commercial application potential due to their attractive advantages of low cost and high stability. However, the power conversion efficiency of C-PSCs is relatively low, mainly due to the poor crystalline quality of the C-PSC applicable perovskite films and the energy level mismatch between the perovskite and carbon electrode. Herein, a moisture-induced secondary crystal growth strategy to simultaneously improve the crystalline quality and optimize the energy level of perovskite film is proposed. The presence of moisture renders the surface of perovskite grains reactive by forming metastable intermediates. It is demonstrated that the commonly considered harmful intermediates can trigger secondary crystal growth. This secondary growth strategy results in improved crystallinity, larger grain size, and better morphology of the perovskite films, which reduce the density of defect states and also benefit the interface contact between the perovskite film and carbon electrode. Furthermore, the secondary growth modulates the surface composition of the film to achieve an optimized energy level alignment. As a result, this secondary growth strategy reduces the charge recombination loss and accelerates the charge transport process in C-PSCs. Consequently, a new record efficiency of 19.52% is achieved for HTL-free C-PSCs.

Perovskite solar cells are still in their infancy due to scarcity of conventional electrode material. Nature-abundant carbon derived electrodes can be well adjusted to perovskite solar cells, which is confirmed by enhanced J–V performance. Furthermore, electrode composite layer assists stability of the device even after water-dipping tests and 750 h under harsh storage conditions (60 °C and 1 sun).

Since the perovskite solar cell (PSC) is emerging as a next-generation photovoltaic, the counter electrode takes a significant role in the commercializing process. Not only the nature abundancy of carbon, but also the proper electronic property and flexibility allow the carbon electrode as a strong candidate for the future electrode. Herein, heat, moisture, and light-resistive electrode-based PSCs are fabricated via tailored elastomer and carbon materials. For device applicable perspective and to fabricate encapsulative electrode, carbon paper and paste obtaining elastomer-based binder (polyisobutylene) are utilized together; both J–V performance up to 17% and long-term stability are enhanced compared to the single-paste system. To confirm the hydrophobicity with encapsulating ability, a direct water-dipping test is conducted and negligible power conversion efficiency (PCE) loss is observed. Last but not least, the optimized device without extra encapsulation exhibits robust stability under harsh conditions retaining ≈80% of initial PCE for 750 h (60 °C and 1 sun), which paves the new concept of carbon electrode as an electrode itself and encapsulating material at the same time.

Introducing the n-type polymer N2200 in PCBM, not only up-shifts the LUMO energy level and enhances the electrical properties of PCBM, but also effectively passivates surface defects on the perovskite layer. PCBM@N2200 devices demonstrate, a V _OC of 1.20 V, leading to an impressive PCE of 24.53% and the corresponding module achieves an efficiency of 20.30% with an active area of 11.19 cm².

Abstract

Phenyl-C61-butyric acid methyl ester (PCBM) remains the most commonly used electron transport layer in inverted perovskite solar cells (IPSCs). However, its insufficient electrical properties and passivation ability limit the device's performance. In this study, it is demonstrated that introducing an appropriate amount of n-type polymer N2200 into the PCBM can simultaneously enhance the electrical properties of PCBM and passivate the defects distributed on perovskite surface. This modification of PCBM leads to improved band alignment and enhanced electron mobility. Simultaneously, N2200 polymer contains electron donors such as O, S involved in passivating uncoordinated Pb²⁺ defects. The PCBM@N2200-based IPSCs exhibit an enhanced open-circuit voltage (V _OC) of 1.20 V with the minimum 0.36 V voltage loss and reach the champion power conversion efficiency (PCE) of 24.53% (certified PCE is 24.05%) with narrow distribution. Impressively, the corresponding module achieves an efficiency of 20.30% (11.19 cm²). Moreover, the PCBM@N2200-based IPSCs maintain 96% of their initial efficiency after operating at the maximum power point for 500 h, thanks to the interfacial passivation, improved uniformity, and increased hydrophobicity resulting from N2200 doping.

Hyperspectral photoluminescence imaging followed by comprehensive data analysis provides access to the spatial distribution of optoelectronic and solar cell parameters without the need for specific electrical measurements. This methodology is presented here and demonstrated using laser-patterned perovskite solar cells as an example.

Absolute calibrated hyperspectral photoluminescence (PL) imaging is utilized to access, in a simple and fast way, the spatial distribution of relevant solar cell parameters such as quasi-Fermi level splitting, optical diode factor, Urbach energies E _u, and shunt resistances R _sh, without the need for electrical measurements. Since these metrics play a significant role in evaluating the process windows for electrical series interconnection by laser patterning, this approach is followed to systematically locate and quantify electrical losses that may occur as a result of the laser-patterning process for monolithic series interconnection. It is shown that both picosecond and nanosecond laser pulses can be used for successful series interconnection. In both cases, only minor lateral material alterations occur, localized in a few μm wide region adjacent to the edges of the scribe lines. Furthermore, the acquisition and analysis of these hyperspectral PL datasets provide insights in the material removal process, from which it is concluded that the perovskite is rather resilient against the thermal impact of the laser.

This study demonstrates a scalable production of efficient and stable perovskite solar modules utilizing scalable fabrication methods, including spray, slot-die, blade, and dip coating. Introducing rubidium chloride to the blade-coated lead iodide precursor assists in uniform perovskite conversion, enabling 17.9% efficiency minimodules with a 37 cm² aperture area.

Perovskite solar modules (PSMs) have shown remarkable photovoltaic potentials, but they still suffer from large power conversion efficiency (PCE) loss on scale-up and instability due to inferior uniformity and crystallization over large areas. Herein, the scalable production of efficient and stable PSMs using a suite of all-scalable fabrication methods featuring a two-step blade/dip-coating approach to deposit the perovskite absorber layer is demonstrated. Rubidium chloride is introduced to embed (PbI₂)₂RbCl complex seeds in the first-deposited PbI₂ precursor, which assists in uniform crystallization of the perovskite layer with high crystallinity and reduced defect density over large areas. Following the optimization of RbCl additives, a champion PSM with 17.9% PCE on a 7.6 × 7.6 cm² substrate with a 37 cm² aperture area is achieved. Moreover, the RbCl-incorporated PSMs demonstrate excellent reproducibility and stability under continuous 1 sun illumination. This work shows that the two-step blade/dip coating is a promising method for producing high-efficiency and stable PSMs on an industrially relevant scale.

Herein, the efficient formamidinium-cesium -based inverted perovskite solar cells are developed by introducing 1-(3-aminopropyl)-imidazole (API) for perovskite bottom interface modulation. The appearance of API not only optimizes the energy band between the PTAA/PVK, but also reduces the perovskite bottom defects. Notably, the formation of hydrogen bonds between R-NH₂ of API and I^- strengthens the binding ability of R-C═N and Pb²⁺ defects.

Abstract

Considering the direct influence of substrate surface nature on perovskite (PVK) film growth, buried interfacial engineering is crucial to obtain ideal perovskite solar cells (PSCs). Herein, 1-(3-aminopropyl)-imidazole (API) is introduced at polytriarylamine (PTAA)/PVK interface to modulate the bottom property of PVK. First, the introduction of API improves the growth of PVK grains and reduces the Pb²⁺ defects and residual PbI₂ present at the bottom of the film, contributing to the acquisition of high-quality PVK film. Besides, the presence of API can optimize the energy structure between PVK and PTAA, which facilitates the interfacial charge transfer. Density functional theory (DFT) reveals that the electron donor unit (R-C ═ N) of the API prefers to bind with Pb²⁺ traps at the PVK interface, while the formation of hydrogen bonds between the R-NH₂ of API and I⁻ strengthens the above binding ability. Consequently, the optimum API-treated inverted formamidinium-cesium (FA/Cs) PSCs yields a champion power conversion efficiency (PCE) of 22.02% and exhibited favorable stability.

A high crystalline and compact narrow-bandgap perovskite film with an area over 100 cm² is prepared by combining compositional, solvent and additive engineering. Based on these films, narrow-bandgap perovskite and all-perovskite tandem mini-modules with an aperture area of 10.4 cm² are constructed and exhibit high efficiencies of 13.2% and 16.4%, respectively.

Abstract

Developing all-perovskite tandem solar cells is an effective approach to extend the limit of power conversion efficiency. However, fast preparation of large-area and high-quality narrow-bandgap Sn-based perovskite films still remains a major challenge in fabricating all-perovskite tandem modules. Here high-crystalline and compact narrow-bandgap perovskite films with an area over 100 cm² are well prepared by combining compositional, solvent and additive engineering. The use of 2-methoxyethanol as a solvent enables the fast deposition of narrow-bandgap perovskite films. Adding proper amounts of dimethyl sulfoxide and surfactant L-α-phosphatidylcholine into the narrow-bandgap perovskite precursor effectively enhances the crystallinity and coverage of the resulting perovskite films, respectively. Based on these studies, narrow-bandgap perovskite and all-perovskite tandem mini-modules with an aperture area of 10.4 cm² are constructed and exhibit high efficiencies of 13.2% and 16.4%, respectively. This study provides an option for fast deposition of high-quality narrow-bandgap perovskite films, which is beneficial for the scalable production of all-perovskite tandem solar modules.

A solution is sought for the buried interface issues within CsPbI₂Br-based perovskite solar cells. Addressing this, a multifunctional electron transporting layer (ETL) using a PbCl₂-modified ZnO nanocomposite is introduced. By tuning bandgap and energy levels, the ETL enhances energy alignment with CsPbI₂Br. Integration of residual PbCl₂ at the buried interface minimizes defects, ameliorating film quality.

Abstract

CsPbI₂Br perovskite solar cells (PSCs) have garnered significant attention owing to their remarkable thermal stability and desirable bandgap. However, CsPbI₂Br-based devices still face critical challenges, particularly at the interfaces between the active layer and adjacent components. In this study, a multifunctional ZnO composition has developed as the electron transporting layer (ETL) for CsPbI₂Br PSCs, enabling simultaneous efficient charge extraction and passivation of buried interface defects in CsPbI₂Br. The nanocomposite, composed of PbCl₂-modified ZnO (PbCl₂-ZnO), facilitates the regulation of bandgap and conduction band to align the energy level of ETL and CsPbI₂Br. Additionally, the residual PbCl₂ at the buried interface of the perovskite incorporates into the perovskite lattice, reducing I defect and thus improving film quality. The improved energy level alignment at the ETL/CsPbI₂Br interface and the suppressed I defect-induced carrier nonradiative recombination result in a remarkable reduction in energy loss from 0.73 to 0.52 eV. Finally, the PbCl₂-ZnO hybrid nanocomposite ETL significantly enhances the efficiency of CsPbI₂Br PSCs, increasing it from 14.15% to 17.46%, representing one of the highest reported power conversion efficiency (PCE) values for CsPbI₂Br PSCs. These findings demonstrate the potential of PbCl₂-ZnO hybrid nanocomposite as an effective ETL for CsPbI₂Br PSCs.

A suitable nanoscale phase-separated morphology with balanced crystalline regions and mixing domains is constructed in an all-polymer-based active layer. The ideal morphology is beneficial to charge transfer and collection. Based on the optimized morphology, an outstanding power conversion efficiency of 18.39% for binary all-perovskite solar cells (AM 1.5G, 100 mW cm⁻²) is achieved.

Abstract

All-polymer solar cells (All-PSCs) are considered to be the most promising candidates for realizing efficient and stable organic solar cells (OSCs). However, the challenge of controlling morphology has hindered the performance of All-PSCs. Compared to small molecule acceptors, polymer acceptors play a more crucial role in obtaining an ideal morphology for All-PSCs. The molecular weight of polymer acceptors is one of the key factors determining the morphological and mechanical properties as well as the interactions with donors. Herein, by using a monomer of PYIT (PYIT1) and PYITs with low (PYIT2) and high (PYIT3) molecular weights, the impact of molecular weight of the polymer acceptor is systematically investigated on the phase transition process, morphological, and photovoltaic properties. It is found that tuning the molecular weight effectively regulates the phase transition process of the polymer acceptor and its interaction with the polymer donor. This induces significant effects on the aggregation behaviors of the polymers. Appropriate molecular weight polymer acceptors can facilitate favorable phase separation morphology. With PBQx-Cl as the donor and PYIT2 as acceptor, a high-performance binary All-PSC is achieved with an efficiency of 18.39%. This study provides deep insights into the performance enhancement of All-PSCs through rational polymer acceptor design.

By introducing ammonium sulfamate between the TiO₂ layer and the perovskite layer as an interface modification material, the energy level distribution of TiO₂ is regulated, the interface defects are passivated, the electrical properties of TiO₂ are improved, and the electron transport ability of TiO₂ layer is promoted. Finally, high-efficiency and stable PSCs are prepared.

Abstract

Defects in perovskite films are still the dominant destroyer of both power conversion efficiency (PCE) and long-term stability in perovskite solar cells (PSCs). As the most popular electron transport layer (ETL), TiO₂ film is used in many PSCs to achieve high PCE. However, pristine TiO₂ by itself is not sufficient as an ETL due to lattice mismatch, poor alignment of the energy level gap, and hysteresis of the PSC. Herein, ammonium sulfamate (AS), with desired NH₄ ⁺ and S═O functional groups, is designed to modify the TiO₂ surface and interface to improve the PCE of PSCs. It is found that the AS works like a seed layer for the perovskite deposition, and, in addition, it effectively forms a bridge between the TiO₂ surface and the perovskite. As a result, PSCs are successfully fabricated with a champion power conversion efficiency of 24.78% with smaller hysteresis. The PSCs prepared using the AS-modified TiO₂ also show excellent stability, and the bare device without any encapsulation retains 96% of its initial PCE after 1056 h of ambient exposure at 25 °C and 25% relative humidity.

An asymmetric heterohalogen-substitution strategy fine-tunes optimizes the bulk heterojunction morphology of organic solar cellss with high power conversion efficiency. Large ‒3 dB bandwidths of 4.11, 3.14, and 3.04 MHz at RGB wavelengths respectively are reported, and concurrent improvements in data rate of up to 302.7 Mb s⁻¹ and power output of 7.38 mW during the visible light communication process.

Abstract

Organic solar cells (OSCs), exhibiting better sensitivity to different light intensities and higher power conversion efficiencies (PCEs) under indoor illumination, have great potential to be simultaneously used for solar energy harvesting and optical communication. However, the poor intrinsic molecular stacking and phase separation in active layers significantly hinder the charge transport and extraction in OSCs for achieving this aim. Here, an effective heterohalogen-substitution asymmetric additive strategy is proposed to fine-tune the non-covalent interaction with nonfullerene molecules and optimize the morphology of active layer, which greatly boosts both the OSC photovoltaic performance with the PCEs of up to 18.30% and 29.52% under AM 1.5G and indoor light illumination respectively, and the ‒3 dB communication bandwidths of 4.11, 3.14, and 3.04 MHz at red, green, and blue (RGB) wavelengths respectively. Of particular note, combining the wavelength division multiplexing and adaptive bit-loading technologies, the visible light communication system comprised of the RGB light sources and additive-treated OSCs delivers more remarkable data throughput of 302.7 Mb s⁻¹ and higher harvesting power of 7.38 mW simultaneously, presenting an excellent self-powered capability for enhanced endurance. This work demonstrates that high-performance OSCs with excellent energy harvesting and wireless communication capacity can be perfectly achieved by a heterohalogen-substitution asymmetric additive strategy.

Asymmetric π-bridge engineering is proposed to improve the permittivity of polymer donors without impairing their miscibility with acceptor materials. Asymmetric π-bridge benzo[1,2-b:4,5-b′]difuran (BDF)-based polymer PBDF-TF-BTz demonstrates larger permittivity, smaller exciton binding energy, and more favorable molecular packing than its counterparts, leading to proficient charge dynamics and a promising power conversion efficiency of 18.10% with a remarkable fill factor of 80.11% for derived devices.

Abstract

Organic solar cells (OSCs) exhibit complex charge dynamics, which are closely correlated with the dielectric constant (ɛ_r) of photovoltaic materials. In this work, a series of novel conjugated copolymers based on benzo[1,2-b:4,5-b′]difuran (BDF) and benzotriazole (BTz) is designed and synthesized, which differ by the nature of π-bridge from one another. The PBDF-TF-BTz with asymmetric furan and thiophene π-bridge demonstrates a larger ɛ_r of 4.22 than PBDF-dT-BTz with symmetric thiophene π-bridge (3.15) and PBDF-dF-BTz with symmetric furan π-bridge (3.90). The PBDF-TF-BTz also offers more favorable molecular packing and appropriate miscibility with non-fullerene acceptor Y6 than its counterparts. The corresponding PBDF-TF-BTz:Y6 OSCs display efficient exciton dissociation, fast charge transport and collection, and reduced charge recombination, eventually leading to a power conversion efficiency of 17.01%. When introducing a fullerene derivative (PCBO-12) as a third component, the PBDF-TF-BTz:Y6:PCBO-12 OSCs yield a remarkable FF of 80.11% with a high efficiency of 18.10%, the highest value among all reported BDF-polymer-based OSCs. This work provides an effective approach to developing high-permittivity photovoltaic materials, showcasing PBDF-TF-BTz as a promising polymer donor for constructing high-performance OSCs.