Chen Weijie

Herein, 5-amino-2-fluorobenzoic acid (5-AFA) is used, which is an organic molecular multifunctional additive with carboxyl (–COOH), amino and fluoro functional groups. The incorporation of the 5-AFA additive into perovskite films demonstrates a promising approach for enhancing the performance of solar cells, which will provide the pioneering investigation for the commercialization of perovskite solar cells.

As the evolution of energy resources continues, perovskite solar cells (PSCs) are gaining increasing attention from researchers and are emerging as strong competitors to silicon-based solar cells. However, due to the preparation process, defects are inevitable and have a significant impact on the efficiency and stability of PSCs. Therefore, it is essential to explore effective passivation strategies to minimize nonradiative recombination, enhance carrier mobility, and improve the overall photovoltaic performance of these cells. Herein, 5-amino-2-fluorobenzoic acid (5-AFA) is incorporated into the perovskite precursor solution as an additive. The aim is to investigate the passivation mechanism of the composite, which involves multifunctional groups such as –COOH, –NH₂, and –F. The results demonstrate that this additive effectively passivates the defects, suppresses nonradiative recombination, slows down the crystallization process, improves film crystallinity, and ultimately enhances both the efficiency and stability of the PSCs. Specifically, the passivated PSCs achieve an impressive power conversion efficiency of 20.37%. These cells also exhibit remarkable stability with the unencapsulated devices maintaining an initial efficiency of 79% even after 700 h in an indoor environment. These findings highlight the successful application of the 5-AFA additive in enhancing the performance and durability of PSCs.

During the process of preparing flexible perovskite solar cells (PSCs) using the solution method, numerous non-radiative recombination centers and uncoordinated Pb⁺ ions are introduced. To address this issue, a 2D perovskite material, methoxy-based passivator 4-methoxyphenethylammonium iodide, is designed, which possesses electron-donating capabilities and can effectively passivate defects. As a result, flexible PSCs with a 3D/2D structure are successfully fabricated, achieving a remarkably high voltage (1.2 eV) and excellent photovoltaic conversion efficiency (23.3%).

As is well known, the interface of perovskite solar cells (PSCs) is rich in deep-level carrier traps, which act as non-radiative recombination centers and limit the open-circuit voltage (V _OC) and power conversion efficiency (PCE) of PSCs. Defect chemistry and surface passivation agents have been extensively studied, primarily focusing on the neutralization of non-coordinated lead or anion defects. Herein, a novel methoxy-based passivator 4-methoxyphenethylammonium iodide (p-MeOPEAI) is introduced for a multifunctional passivation effect at the perovskite interface. It is susceptible for p-MeOPEAI to form 2D perovskite on top of 3D perovskite, and it interacts with the surface of 3D perovskite in multiple ways, forming a 3D/2D structure that facilitates charge transfer and p-MeOPEAI passivates the uncoordinated Pb²⁺ ions of the perovskite film surface. The interface defects in the PSCs are well passivated, minimizing non-radiative recombination and enhancing device performance. As a result, a champion PCE of 23.3% is achieved for flexible PSCs with a high V _OC (1.2 V). In addition, modified devices also show enhanced operational mechanical stability (retention of >80% initial PCE after 10 000 bending cycles).

The review focuses on strain in flexible perovskite solar cells (f-PSCs) including strain sources, strain characterization analysis, strain effects, and means of utilizing/controlling strain. The potential application scenarios of f-PSCs and the optimization direction of high-performance devices are summarized. The authors provide key insights and future perspectives for this important field.

Abstract

Flexible perovskite solar cells (f-PSCs) as a promising power source have grabbed surging attention from academia and industry specialists by integrating with different wearable and portable electronics. With the development of low-temperature solution preparation technology and the application of different engineering strategies, the power conversion efficiency of f-PSCs has approached 24%. Due to the inherent properties and application scenarios of f-PSCs, the study of strain in these devices is recognized as one of the key factors in obtaining ideal devices and promoting commercialization. The strains mainly from the change of bond and lattice volume can promote phase transformation, induce decomposition of perovskite film, decrease mechanical stability, etc. However, the effect of strain on the performance of f-PSCs has not been systematically summarized yet. Herein, the sources of strain, evaluation methods, impacts on f-PSCs, and the engineering strategies to modulate strain are summarized. Furthermore, the problems and future challenges in this regard are raised, and solutions and outlooks are offered. This review is dedicated to summarizing and enhancing the research into the strain of f-PSCs to provide some new insights that can further improve the optoelectronic performance and stability of flexible devices.

Here, the authors summarize the current state of printable organic and perovskite solar cells and shared their view regarding the challenges and prospects toward commercialization. Different printing techniques involving the correlation between material properties and printing mechanisms are analyzed. The authors also discuss the optimization of ink formulation, large-area film deposition, and design of module structure.

Abstract

Photovoltaic technology presents a sustainable solution to address the escalating global energy consumption and a reliable strategy for achieving net-zero carbon emissions by 2050. Emerging photovoltaic technologies, especially the printable organic and perovskite solar cells, have attracted extensive attention due to their rapidly transcending power conversion efficiencies and facile processability, providing great potential to revolutionize the global photovoltaic market. To accelerate these technologies to translate from the laboratory scale to the industrial level, it is critical to develop well-defined and scalable protocols to deposit high-quality thin films of photoactive and charge-transporting materials. Herein, the current state of printable organic and perovskite solar cells is summarized and the view regarding the challenges and prospects toward their commercialization is shared. Different printing techniques are first introduced to provide a correlation between material properties and printing mechanisms, and the optimization of ink formulation and film-formation during large-area deposition of different functional layers in devices are then discussed. Engineering perspectives are also discussed to analyze the criteria for module design. Finally, perspectives are provided regarding the future development of these solar cells toward practical commercialization. It is believed that this perspective will provide insight into the development of printable solar cells and other electronic devices.

A weak coordination solvent strategy is developed to tailor solvent–perovskite coordination. This strategy promotes the direct crystallization from sol–gel phases to α-formamidinium lead iodide (FAPbI₃), leads to more balanced nucleation–growth kinetics, and restrains the formation of defects and microstrains in situ. The corresponding ambient-printed FAPbI₃ perovskite solar cells exhibit a remarkable power conversion efficiency of 24%.

Abstract

The critical requirement for ambient-printed formamidinium lead iodide (FAPbI₃) lies in the control of nucleation–growth kinetics and defect formation behavior, which are extensively influenced by interactions between the solvent and perovskite. Here, a strategy is developed that combines a cosolvent and an additive to efficiently tailor the coordination between the solvent and perovskite. Through in situ characterizations, the direct crystallization from the sol–gel phase to α-FAPbI₃ is illustrated. When the solvent exhibits strong interactions with the perovskite, the sol–gel phases cannot effectively transform into α-FAPbI₃, resulting in a lower nucleation rate and confined crystal growth directions. Consequently, it becomes challenging to fabricate high-quality void-free perovskite films. Conversely, weaker solvent–perovskite coordination promotes direct crystallization from sol–gel phases to α-FAPbI₃. This process exhibits more balanced nucleation–growth kinetics and restrains the formation of defects and microstrains in situ. This strategy leads to improved structural and optoelectronic properties within the FAPbI₃ films, characterized by more compact grain stacking, smoother surface morphology, released lattice strain, and fewer defects. The ambient-printed FAPbI₃ perovskite solar cells fabricated using this strategy exhibit a remarkable power conversion efficiency of 24%, with significantly reduced efficiency deviation and negligible decreases in the stabilized output.

Incorporation of a self-assembled monolayer at the interface in mesoscopic perovskite solar cells (PSCs) results in simultaneous enhancement of mechanical reliability, operational-stability, and power-conversion efficiency (PCE). Threefold increase in the interfacial toughness in a PSC with PCE of over 24% is responsible for T80 (duration at 80% initial PCE retained) of ≈18 000 h. Possible underlying mechanisms are elucidated.

Abstract

The combined effects of compact TiO₂ (c-TiO₂) electron-transport layer (ETL) are investigated without and with mesoscopic TiO₂ (m-TiO₂) on top, and without and with an iodine-terminated silane self-assembled monolayer (SAM), on the mechanical behavior, opto–electronic properties, photovoltaic (PV) performance, and operational-stability of solar cells based on metal-halide perovskites (MHPs). The interfacial toughness increases almost threefold in going from c-TiO₂ without SAM to m-TiO₂ with SAM. This is attributed to the synergistic effect of the m-TiO₂/MHP nanocomposite at the interface and the enhanced adhesion afforded by the iodine-terminated silane SAM. The combination of m-TiO₂ and SAM also offers a significant beneficial effect on the photocarriers extraction at the ETL/MHP interface, resulting in perovskite solar cells (PSCs) with power-conversion efficiency (PCE) of over 24% and 20% for 0.1 and 1 cm² active areas, respectively. These PSCs also have exceptionally long operational-stability lives: extrapolated T80 (duration at 80% initial PCE retained) is ≈18 000 and 10 000 h for 0.1 and 1 cm² active areas, respectively. Postmortem characterization and analyses of the operational-stability-tested PSCs are performed to elucidate the possible mechanisms responsible for the long operational-stability.

The antenna effect-mediated lanthanide–organic frameworks Tb-cpon greatly broaden the full-spectrum utilization and UV light sensitivity of the perovskite solar cells (PSCs) through the Förster resonance energy transfer process and energy downconversion effect. Structurally transformed 3D supramolecular skeletons as growth templates in perovskite crystallization maintain high efficiency and UV stability of PSCs under operating conditions by eliminating grain-boundary defects.

Abstract

In this work, the ligand-to-metal charge transition and Förster resonance energy transfer process is exploited to derive lanthanide–organic framework (Tb-cpon) modified perovskite solar cells (PSCs) with enhanced performance under UV irradiation. Tb-cpon-modified PSCs exhibit rapid response and reduced degradation due to energy downconversion facilitated by effective coupling of UV-sensitive chromophores to lanthanide luminescent centers, enhancing the spectral response range of the composite films. Furthermore, the characteristic changes of precursor particle sizes suggest formation of Tb-cpon adducts as intermediate products, leading to enhanced crystallinity and reduced defect concentrations in the Tb-cpon-perovskite hybrid film. Accordingly, the Tb-cpon-modified PSC devices obtain a champion efficiency up to 23.72% as well as a sensitive photovoltaic conversion even under pure UV irradiation. Moreover, the unencapsulated devices maintain more than 80% of the initial efficiency after continuous irradiation under a 310 nm UV lamp for 24 h (from the Au electrode side), compared to 21% for the control devices.

Pseudo planar heterojunction (P-PHJ) is successfully fabricated by binary-dilution strategy (PM6 is mixed with micro acceptor BO-4Cl and L8-BO is mixed with micro donor PM6, respectively), which not only remains donor/acceptor (D/A) vertical distribution of binary planar heterojunction (P-BHJ), but gains larger D/A interpenetrating regions. The formation of ideal active layer morphology promotes excellent charge dynamics, and boosts the PCE of P-PHJ from 17.67% to 19.32%.

Abstract

The sequential deposition process has demonstrated the great possibility to achieve a photolayer architecture with an ideal gradient phase separation morphology, which has a vital influence on the physical processes that determine the performance of organic solar cells (OSCs). However, the controllable preparation of pseudo-planar heterojunction (P-PHJ) with gradient distribution has not been effectively elucidated. Herein, a binary-dilution strategy is proposed, the PM6 solution with micro acceptor BO-4Cl and the L8-BO solution with micro donor PM6 respectively, to form P-PHJ film. This architecture exists good donor (D) and acceptor (A) vertical gradient distribution and larger D/A interpenetrating regions, which promotes exciton generation and dissociation, shortens charge transport distance and optimizes carrier dynamics. Moreover, the dilution of PM6 by BO-4Cl promotes the regulation of active layer aggregation size and phase purity, thus alleviating energy disorder and voltage loss. As a result, the P-PHJ device exhibits an outstanding power conversion efficiency of 19.32% with an excellent short-circuit current density of 26.92 mA cm⁻², much higher than planar binary heterojunction (17.67%) and ternary bulk heterojunction (18.49%) devices. This research proves a simple but effective method to provide an avenue for constructing desirable active layer morphology and high-performance OSCs.

The synergistic strategies of the regional selenium isomerization and asymmetric crystal engineering are applied to synthesize isomeric small molecular acceptors. Benefiting from optimized crystal packing, favourable morphology and ordered molecular arrangement, A-OSeF-based binary organic solar cells yield a champion efficiency of 18.5 % and low energy loss among selenium-containing acceptors.

Abstract

Both the regional isomerization and selenium-substitution of the small molecular acceptors (SMAs) play significant roles in developing efficient organic solar cells (OSCs), while their synergistic effects remain elusive. Herein, we developed three isomeric SMAs (S-CSeF, A-ISeF, and A-OSeF) via subtly manipulating the mono-selenium substituted position (central, inner, or outer) and type of heteroaromatic ring on the central core by synergistic strategies for efficient OSCs, respectively. Crystallography of asymmetric A-OSeF presents a closer intermolecular π–π stacking and more ordered 3-dimensional network packing and efficient charge-hopping pathways. With the successive out-shift of the mono-selenium substituted position, the neat films give a slightly wider band gap and gradually higher crystallinity and electron mobility. The PM1 : A-OSeF afford favourable fibrous phase separation morphology with more ordered molecular packing and efficient charge transportation compared to the other two counterparts. Consequently, the A-OSeF-based devices achieve a champion efficiency of 18.5 %, which represents the record value for the reported selenium-containing SMAs in binary OSCs. Our developed precise molecular engineering of the position and type of selenium-based heteroaromatic ring of SMAs provides a promising synergistic approach to optimizing crystal stacking and boosting top-ranked selenium-containing SMAs-based OSCs.

Publication date: January 2024

Source: Journal of Energy Chemistry, Volume 88

Author(s): Yahui Zhang, Yafeng Li, Ruixiang Peng, Yi Qiu, Jingyu Shi, Zhenyu Chen, Jinfeng Ge, Cuifen Zhang, Zheng Tang, Ziyi Ge

Publication date: 15 November 2023

Source: Joule, Volume 7, Issue 11

Author(s): Ming-Hua Li, Shuo Wang, Xinbo Ma, Run Long, Jinpeng Wu, Mingyue Xiao, Jiaju Fu, Zhe Jiang, Gang Chen, Yan Jiang, Jin-Song Hu

This review highlights the significance of developing functional additives for rigid perovskite solar cells and flexible perovskite solar cells, which are expected to enhance the robustness of perovskite solar cells and promote their large-scale industrialization in the near future.

In the past decade, perovskite solar cells (PSCs), exhibiting high efficiency, low cost, and flexibility, have made inspiring signs of progress and show great potential in large-scale commercialization as representative third-generation photovoltaic technology. Nevertheless, due to rapid crystallization of perovskite crystals through the solution film-forming technique, a primary challenge is the fabrication of excellent perovskite films with superior optoelectronic characteristics and good flexibility. However, the defects and lattice stresses generated in the perovskite layer during rapid crystallization might diminish the efficiency, robustness, and reliability of PSCs. To date, a variety of techniques are being identified for strengthening the quality of perovskite films, which include interfacial engineering, solvent engineering, doping, and additives engineering. Among these strategies, developing effective additives is of utmost importance in controlling the kinetics of perovskite film crystallization, leading to improved device performance and mechanical stability, especially for flexible PSCs (FPSCs). Herein, the state-of-the-art additives developed in PSCs during the past few years are retrospected, such as ionic liquids, polymers, and small organic molecules, and particular attention is paid to the advanced progress of additive engineering in FPSCs. Moreover, critical perspectives are put forward on the opportunities and challenges of additive engineering in the future development of PSCs.

Additive-free 2,2′,7,7′-tetrakis (N, N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene@poly(3-hexylthiophene) (Spiro-OMeTAD@P3HT) composite is employed as hole-transporting layer (HTL) to construct the fully ambient solution-processed carbon-electrode-based perovskite solar cells (C-PSCs), and NiO _x is used as the top HTL/buffer layer to protect HTL from being corroded by carbon-pastes. Benefiting from the improved film quality and optimized band alignment of Spiro-OMeTAD@P3HT composite HTL, the resultant C-PSCs yield a champion efficiency of 19%.

Hole-transporting layer (HTL) plays a critical role in determining the device performance of carbon-electrode-based perovskite solar cells (C-PSCs). However, the use of best-performing organic HTL (such as 2,2′,7,7′-tetrakis (N, N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene [Spiro-OMeTAD] or poly(3-hexylthiophene) [P3HT]) for efficient and stable C-PSCs remains challenging due to the hygroscopic additives, unfavorable band alignments, and corrosive carbon pastes. Herein, the additive-free Spiro-OMeTAD/P3HT composite (denoted as Spiro@P3HT) is employed as HTL to construct the fully ambient solution-processed C-PSCs, and NiO _x is used as top HTL/buffer layer that protects P3HT from being corroded by carbon pastes. As compared to pristine P3HT, the incorporation of Spiro-OMeTAD not only smooths the HTL morphology, but also shifts down the highest occupied molecular orbital level, thus forming a more energy-favorable cascade that maximizes hole extraction at the perovskite/HTL interface and minimizes recombination loss. Consequently, the target C-PSCs with optimal Spiro@P3HT composite HTL achieve a champion efficiency of 19%. More importantly, benefiting from the self-sealing protection of hydrophobic Spiro@P3HT HTL and carbon electrode, the target C-PSCs exhibit no noticeable performance degradation after storage in ambient air for 1440 h and continuous operation under illumination for 350 h. In this work, a facile way is provided to develop robust and efficient additive-free HTL toward fully solution-processing high-performance C-PSCs.

In this work, the impact of methylammonium chloride (MACl) addition into quasi 2D/3D tin-based perovskite films and devices is investigated. The inclusion of chloride into the perovskite lattice is demonstrated and its effects on the crystallization and optoelectronic properties of the tin-based perovskite are elucidated. The addition of MACl amounts up to 35 mol% impacts the morphology, crystallinity, and device efficiency.

In the quest for perovskite materials with reduced toxicity, Sn perovskites are emerging. However, they suffer from material instability and rapid crystallization, leading to high defect densities in the films. In this work, the methylammonium chloride (MACl)-assisted crystallization as a route to improve stability and optoelectronic quality of quasi 2D/3D PEA_0.08FA_0.92SnI₃ perovskite is demonstrated. For an optimal additive amount (10 mol%), a 37% increase in power conversion efficiency is found. Notably, MACl enhances the films' stability, evidenced by temporal PL tracking. Understanding the effect of MACl addition in this system is interesting for the pursuit of efficient and stable tin-based devices. The investigations show that MACl addition causes a shift in the optical bandgap and improves morphology, indicating effects in the bulk crystal structure. X-ray photoelectron spectroscopy confirms the presence of Cl on the surface, but no indication of MA⁺ is found. Intriguingly, UV photoelectron spectroscopy shows pronounced changes in the density of states. For the first time, it is shown that MACl promotes the formation of a two-dimensional layer via the surface accumulation of PEA⁺. The MACl additive lowers the absorber's ionization energy, possibly facilitating hole extraction. Overall, this work highlights a facile route to control the crystallization of Sn perovskites.

The isomerized solid additive engineering based on volatile dithienothiophene (DTT) isomers is empolyed to achieve a remarkable PCE of 18.72% for all-PSCs processed with green solvent. More importantly, the all-PSCs fabricated with this approach offer excellent compatibility with large-area blade-coating techniques, and demonstrate exceptional thermal stability with extrapolated T ₈₀ lifetime of 14 000 h.

Abstract

Laboratory-scale all-polymer solar cells (all-PSCs) have exhibited remarkable power conversion efficiencies (PCEs) exceeding 19%. However, the utilization of hazardous solvents and nonvolatile liquid additives poses challenges for eco-friendly commercialization, resulting in the trade-off between device efficiency and operation stability. Herein, an innovative approach based on isomerized solid additive engineering is proposed, employing volatile dithienothiophene (DTT) isomers to modulate intermolecular interactions and facilitate molecular stacking within the photoactive layers. Through elucidating the underlying principles of the DTT-induced polymer assembly on molecular level, a PCE of 18.72% is achieved for devices processed with environmentally benign solvents, ranking it among the highest record values for eco-friendly all-PSCs. Significantly, such superiorities of the DTT-isomerized strategy afford excellent compatibility with large-area blade-coating techniques, offering a promising pathway for industrial-scale manufacturing of all-PSCs. Moreover, these devices demonstrate enhanced thermal stability with a promising extrapolated T ₈₀ lifetime of 14 000 h, further bolstering their potential for sustainable technological advancement.

Zwitterion formamidine sulfinic acid (FSA) as an additive is able to modulate the crystallization of wide-bandgap perovskite films while passivating defects. This suppresses nonradiative recombination and reduces open-circuit voltage (V _OC) loss, achieving efficiencies of 22.06% with a high V _OC of 1.25 V for 1.68 eV perovskite solar cells and 28.81% for perovskite/silicon tandem solar cells.

Wide-bandgap (WBG) perovskite solar cells (PSCs) can be combined with other narrow-bandgap cells to form tandem solar cells (TSCs), which have excellent commercialization prospects. However, the component of WBG perovskite is complex, and the crystallization process is difficult to control. Various bulk and surface defects in polycrystalline films lead to severe nonradiative recombination of photogenerated carriers, resulting in severe open-circuit voltage (V _OC) loss in WBG PSCs. Herein, a zwitterionic additive is introduced to alleviate the V _OC deficit. The sulfinyl group (–SO) in formamidine sulfinic acid (FSA) has a robust interaction with Pb²⁺, which retards the crystallization and improves the crystal quality in perovskite films. Furthermore, FSA has negatively charged centers (–SO₂ ⁻) and positively charged centers (–C(NH₂)₂ ⁺), which can passivate the halogen and cation vacancies, respectively. The improved crystalline quality and passivated defects reduce the capture of carriers by defects and facilitate higher V _OC. With this strategy, the 1.68 eV bandgap PSCs achieve a champion efficiency of 22.06% and a high V _OC of 1.25 V (V _OC loss = 0.43 V). Moreover, the 2-terminal perovskite/silicon TSCs are fabricated with an extraordinary power conversion efficiency of 28.81%.

A novel hole transport material (HTM) based on N-C=O resonance structure is designed for modulation the crystallization and bottom-surface defects of perovskite films. Benefiting from the resonance interconversion (N–C=O and N⁺=C–O⁻) in HTM, the large-area inverted perovskite solar cells (IPSCs) reach a high power conversion efficiency (PCE) up to 21.0% with excellent photo-thermal stability.

Abstract

Upscaling efficient and stable perovskite films is a challenging task in the industrialization of perovskite solar cells partly due to the lack of high-performance hole transport materials (HTMs), which can simultaneously promote hole transport and regulate the quality of perovskite films especially in inverted solar cells. Here, a novel HTM based on N–C = O resonance structure is designed for facilitating the modulation of the crystallization and bottom-surface defects of perovskite films. Benefiting from the resonance interconversion (N–C = O and N⁺ = C–O⁻) in donor-resonance-donor (D-r-D) architecture and interactions with uncoordinated Pb²⁺ in perovskite, the resulting D-r-D HTM with two donor units exhibits not only excellent hole extraction and transport capacities, but also efficient crystallization modulation of perovskite for high-quality photovoltaic films in large area. The D-r-D HTM-based large-area (1.02 cm²) devices exhibit high power conversion efficiencies (PCEs) up to 21.0%. Moreover, the large-area devices have excellent photo-thermal stability, showing only a 2.6% reduction in PCE under continuous AM 1.5G light illumination at elevated temperature (≈65 °C) for over 1320 h without encapsulation.

A ternary-device design is proposed that fully utilizes the individual thermodynamic properties of both dimeric acceptor and monomeric acceptor. The high T _g value of dimeric acceptor significantly impedes the molecular movement of monomeric acceptor, while hypermiscible properties of monomeric acceptor promote percolation of the mixed domain for enhancing charge dynamics.

Abstract

Polymer solar cells (PSCs) are promising for efficient solar energy conversion, but achieving high efficiency and device longevity within a bulk-heterojunction (BHJ) structure remains a challenge. Traditional small-molecule acceptors (SMAs) in the BHJ blend show thermodynamic instability affecting the morphology. In contrast, tethered SMAs exhibit higher glass transition temperatures, mitigating these concerns. Yet, they might not integrate well with polymer donors, causing pronounced phase separation and overpurification of mixed domains. Herein, a novel ternary device is introduced that uses DY-P2EH, a tethered dimeric SMA with conjugated side-chains as host acceptor, and BTP-ec9, a monomeric SMA as secondary acceptor, which respectively possess hypomiscibility and hypermiscibility with the polymer donor PM6. This unique combination affords a parallel-connected ternary BHJ blend, leading to a hierarchical and stable morphology. The ternary device achieves a remarkable fill factor of 80.61% and an impressive power conversion efficiency of 19.09%. Furthermore, the ternary device exhibits exceptional stability, retaining over 85% of its initial efficiency even after enduring 1100 h of thermal stress at 85 °C. These findings highlight the potential advantage of tethered SMAs in the design of ternary devices with a refined hierarchical structure for more efficient and durable solar energy conversion technologies.

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part A

Author(s): Geping Qu, Ying Qiao, Jie Zeng, Siyuan Cai, Qian Chen, Deng Wang, Danish Khan, Limin Huang, Baomin Xu, Jiangzhao Chen, Tarek El-Assaad, Yang-Gang Wang, Dominic V. McGrath, Zong-Xiang Xu

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part A

Author(s): Ya Wang, Bo Zhou, Meidouxue Han, Juntao Zhao, Rongbo Wang, Jiawei Zhang, Huizhi Ren, Guofu Hou, Yi Ding, Ying Zhao, Xiaodan Zhang

This work introduces industrial solvent fractionated LignoBoost kraft lignin (KL) in highly efficient organic solar cells (OSCs) by binary cathode interface layer (CIL) strategy, which can significantly improve the stability of both binary and ternary photoactive layer (PAL) OSC, owing to the passivation of diffusion and reaction between bathocuproine (BCP) and nonfullerene acceptors (NFAs). The results combine sustainable wood-based material with classic interface materials in advance NFA-OSCs.

Abstract

Herein, a binary cathode interface layer (CIL) strategy based on the industrial solvent fractionated LignoBoost kraft lignin (KL) is adopted for fabrication of organic solar cells (OSCs). The uniformly distributed phenol moieties in KL enable it to easily form hydrogen bonds with commonly used CIL materials, i.e., bathocuproine (BCP) and PFN-Br, resulting in binary CILs with tunable work function (WF). This work shows that the binary CILs work well in OSCs with large KL ratio compatibility, exhibiting equivalent or even higher efficiency to the traditional CILs in state of art OSCs. In addition, the combination of KL and BCP significantly enhanced OSC stability, owing to KL blocking the reaction between BCP and nonfullerene acceptors (NFAs). This work provides a simple and effective way to achieve high-efficient OSCs with better stability and sustainability by using wood-based materials.

A stabilizing additive for triple-cation perovskite solar cells is identified that increases both performance and stability. These observations are supported by temperature-dependent investigations of charge carrier mobility using microwave conductivity and open-circuit voltage decay.

Abstract

Besides further improvement in the power conversion efficiency (PCE) of perovskite solar cells (PSC), their long-term stability must also be ensured. Additives such as organic cations with halide counter anions are considered promising candidates to address this challenge, conferring both higher performance and increased stability to perovskite-based devices. Here, a stabilizing additive (N,N-dimethylmethyleneiminium chloride, [Dmmim]Cl) is identified, and its effect on charge carrier mobility and lifetime under thermal stress in triple cation perovskite (Cs_0.05MA_0.05FA_0.90PbI₃) thin films is investigated. To explore the fundamental mechanisms limiting charge carrier mobility, temperature-dependent microwave conductivity measurements are performed. Different mobility behaviors across two temperature regions are revealed, following the power law T^m, indicating two different dominant scattering mechanisms. The low-temperature region is assigned to charge carrier scattering with polar optical phonons, while a strong decrease in mobility at high temperatures is due to dynamic disorder. The results obtained rationalize the improved stability of the [Dmmim]Cl-doped films and devices compared to the undoped reference samples, by limiting temperature-activated mobile ions and retarding degradation of the perovskite film.

A full-scale defect passivation method that consists of an additive engineering strategy and two-stage annealing treatment is developed to passivate defects. Both deep- and shallow-level defects in the bulk, at the surface, and grain boundaries are passivated with improved energetic alignment and reduced non-radiative recombination. The devices achieve a champion efficiency of 24.20%, accompanied by greatly improved humidity, thermal, and illumination stabilities.

Abstract

Despite remarkable progress in perovskite solar cells (PSCs), the unsatisfying stability strongly interrelated with the defect density remains the main obstacle for commercialization. Herein, a synergetic defect passivation method is judiciously designed that consists of a precursor engineering strategy based on an ionic liquid 1-butylsulfonate-3-methylimidazolium dihydrogen phosphate (BMDP), and two-stage annealing (TSA) treatment to sufficiently passivate defects and enhance performance further. It is found that the multifunctional groups from BMDP have strong chemical interactions and form chelated complexes with perovskite components thus effectively passivating the intrinsic defects. Synergized by the sequential TSA treatment, the formed hydrophobic complexes can be precisely controlled with filling along grain boundaries (GBs) and on surfaces, leading to a wrapping of perovskite grains and significant passivation of GBs. Consequently, both deep- and shallow-level defects in the bulk, at GBs and surface are sufficiently passivated, resulting in a champion efficiency of 24.20%. Impressively, the resultant unencapsulated films and corresponding devices exhibit admirable stability with maintaining 83.9% of initial composition for 4000 h of aging in moist air, 81.7% original structure after continuous heating for 1600 h, and 97% initial power conversion efficiency for 1000 h under continuous illumination. This work provides an efficient strategy toward improved efficiency and stability PSCs.

An improved device reproducibility in addition to the power conversion efficiency improvement can be achieved by a sequential deposited process for organic solar cells. The interpenetrating donor/acceptor interfaces and reduced surface roughness result in more uniform charge transfer, charge dissociation, and charge transport processes of layer-by-layer (LBL) films. Meanwhile, the LBL processed ternary devices exhibit broad third component tolerance.

Abstract

The reproducibility issue is impeding the progress of commercialization in organic photovoltaic (OPV) devices, as the difficulty in precise micro-nano structure control in bulk heterojunction films, as well as the ineluctable fluctuations of molecular weight and polydispersity index in the synthetic process. Due to such intrinsic properties, the poor regioregularity significantly affects the batch-to-batch variation in performance of large-area or integrative scattered OPV devices. Seeking alternatives as compensatory strategies is expected to reduce the inevitable problem of reproducibility in the fabrication process. Herein, the application potential of a pseudo-bilayer structure in high-performance OPVs, by using the solution-processed method is thoroughly examined, and it is observed that the sequentially-deposited solar cells enjoy improve device reproducibility in addition to the power conversion efficiency (PCE) enhancement. Importantly, such desirable reproducibility in layer-by-layer structures raised from the film formation process provides new opportunities in ternary OPV devices, and an improved PCE of 18.70% can be achieved in a PM6/L8-BO:PY-IT device, where the counterpart ternary cases exhibit a decreasing trend in performance with the increasing content of PY-IT. This work illustrates the spatial effects of pseudo-bilayer OPV devices in the aspect of charge carrier transport/transfer, morphology and film formation kinetics, and provides a novel perspective to overcome the barriers to commercialization.

Near-infrared photon-assisted annealing facilitates high-performance binary organic solar cells with an impressive efficiency of 19.25% under mild conditions, which allows selectively tuning the molecular ordering of narrow bandgap acceptors within polymer networks to achieve optimal morphologies.

Abstract

Achieving precise control over the nanoscale morphology of bulk heterojunction films presents a significant challenge for the conventional post-treatments employed in organic solar cells (OSCs). In this study, a near-infrared photon-assisted annealing (NPA) strategy is developed for fabricating high-performance OSCs under mild processing conditions. It is revealed a top NIR light illumination, together with the bottom heating, enables the selective tuning of the molecular arrangement and assembly of narrow bandgap acceptors in polymer networks to achieve optimal morphologies, as well as the acceptor-rich top surface of active layers. The derived OSCs exhibit a remarkable power conversion efficiency (PCE) of 19.25%, representing one of the highest PCEs for the reported binary OSCs so far. Moreover, via the NPA strategy, it has succeeded in accessing top-illuminated flexible OSCs using thermolabile polyethylene terephthalate from mineral water bottles, displaying excellent mechanical stabilities. Overall, this work will hold the potential to develop organic solar cells under mild processing with various substrates.

Publication date: 15 November 2023

Source: Joule, Volume 7, Issue 11

Author(s): Guoliang Wang, Jianghui Zheng, Weiyuan Duan, Jiong Yang, Md Arafat Mahmud, Qing Lian, Shi Tang, Chwenhaw Liao, Jueming Bing, Jianpeng Yi, Tik Lun Leung, Xin Cui, Hongjun Chen, Feng Jiang, Yulan Huang, Andreas Lambertz, Marko Jankovec, Marko Topič, Stephen Bremner, Yuan-Zhu Zhang