Chen Weijie

An efficient buried interface modification strategy using a multifunctional modifier is demonstrated, which can comprehensively improve the tin perovskite film and promote charge transport, thereby remarkably enhancing the efficiency of tin perovskite solar cells.

Abstract

Tin perovskite solar cells (PSCs) are considered promising candidates to promote lead-free perovskite photovoltaics. However, their power conversion efficiency (PCE) is limited by the easy oxidation of Sn²⁺ and low quality of tin perovskite film. Herein, an ultra-thin 1-carboxymethyl-3-methylimidazolium chloride (ImAcCl) layer is used to modify the buried interface in tin PSCs, which can induce multifunctional improvements and remarkably enhance the PCE. The carboxylate group (CO) and the hydrogen bond donor (NH) in ImAcCl can interact with tin perovskites, thus significantly suppressing the oxidation of Sn²⁺ and reducing the trap density in perovskite films. The interfacial roughness is reduced, which contributes to a high-quality tin perovskite film with increased crystallinity and compactness. In addition, the buried interface modification can modulate the crystal dimensionality, favoring the formation of large bulk-like crystals instead of low-dimensional ones in tin perovskite films. Therefore, the charge carrier transport is effectively promoted and the charge carrier recombination is suppressed. Eventually, tin PSCs show a remarkably enhanced PCE from 10.12% to 12.08%. This work highlights the importance of buried interface engineering and provides an effective way to realize efficient tin PSCs.

Publication date: September 2023

Source: Journal of Energy Chemistry, Volume 84

Author(s): Yiming Xiong, Haoyu Cai, Wang Yue, Wenjian Shen, Xuehao Zhu, Juan Zhao, Fuzhi Huang, Yi-Bing Cheng, Jie Zhong

Publication date: 14 September 2023

Source: Chem, Volume 9, Issue 9

Author(s): Lijiao Ma, Huifeng Yao, Jianqi Zhang, Zhihao Chen, Jingwen Wang, Jiawei Qiao, Shijie Wang, Zhaozhao Bi, Zi Li, Xiaotao Hao, Zhixiang Wei, Wei Ma, Jianhui Hou

A thorough understanding of the blade coating process is established based on a systematic investigation of individual blade coating parameter on the dried film thickness and uniformity of blade-coated SnO₂ layers for perovskite solar cells. Optimization of the blade coating parameters minimizes thickness gradients along the coating direction, enabling uniform efficiencies on large substrates.

The low-cost and fully solution-based perovskite photovoltaic devices can be upscaled by using the blade coating method. However, control of the charge transport layers thickness on nanometer scale is challenging since the inherent nature of the blade coating process unavoidably induces thickness gradients along the coating direction of blade coated layer. Herein, the film thickness and the uniformity of blade-coated SnO₂ colloidal dispersions in the Landau–Levich regime are systematically studied by varying the substrate temperature, the dispensed solution volume, and the solution concentration as well as the coating speed. It is shown that the advancing meniscus height heavily influences the SnO₂ film thickness. As the solution is consumed during the coating process, the meniscus height decreases and hence the film thickness, yielding poor uniformity of the blade-coated layer. To improve the thickness uniformity, the dispensed solution volume is used to reduce the alteration of the advancing meniscus height along the coating direction and minimize the capillary flow with the appropriate substrate temperature. This study provides crucial insights toward the successful upscaling of perovskite solar cells by blade coating.

Perovskite solar cells (PSCs) are promising for tandem solar cells. For the commercialization, it is essential to fabricate high performance of wide bandgap Pb-free PSCs. In this review, the study of wide bandgap lead-free PSCs is focused. This review will provide a new perspective on the next generation of ecofriendly and non-toxic PSCs.

Abstract

A tandem solar cell, which is composed of a wide bandgap (WBG) top sub-cell and a narrow bandgap (NBG) bottom subcell, harnesses maximum photons in the wide spectral range, resulting in higher efficiency than single-junction solar cells. WBG (>1.6 eV) perovskites are currently being studied a lot based on lead mixed-halide perovskites, and the power conversion efficiency of lead mixed-halide WBG perovskite solar cells (PSCs) reaches 21.1%. Despite the excellent device performance of lead WBG PSCs, their commercialization is hampered by their Pb toxicity and low stability. Hence, lead-free, less toxic WBG perovskite absorbers are needed for constructing lead-free perovskite tandem solar cells. In this review, various strategies for achieving high-efficiency WBG lead-free PSCs are discussed, drawing inspiration from prior research on WBG lead-based PSCs. The existing issues of WBG perovskites such as V _OC loss are discussed, and toxicity issues associated with lead-based perovskites are also addressed. Subsequently, the natures of lead-free WBG perovskites are reviewed, and recently emerged strategies to enhance device performance are proposed. Finally, their applications in lead-free all perovskite tandem solar cells are introduced. This review presents helpful guidelines for eco-friendly and high-efficiency lead-free all perovskite tandem solar cells.

Multifunctional Ti₃C₂T _x MXene material is employed as the buried interface to promote the crystallinity of CsPbI_3−xBr _x perovskite, which can effectively modulate the crystallized dynamics process of the perovskite film, accelerate the charge extraction, and realize an ideal energy-level alignment. Consequently, the as-fabricated CsPbI_3−xBr _x perovskite solar cells demonstrate 19.56% power conversion efficiency whilst excellent UV stability.

Abstract

Despite inorganic CsPbI_3−x Br _x perovskite solar cells (PSCs) being promising in thermal stability, the perovskite degradation and severe nonradiative recombination at the interface hamper their further development. Herein, the typical MXene material, that is, Ti₃C₂T _x , is employed to be the buried interface prior to the perovskite absorber layer in the device, which multi-functionalizes the as-prepared electron-transfer layers by means of both fascinating preferential crystallization of perovskite and/or accelerating the charge extraction with respect to an ideal energy-level alignment and suppressed trap states. Accordingly, the power conversion efficiency of the modified PSC device is substantially enhanced by as high as 19.56% in comparison to their counterparts with only the pristine CsPbI_3−x Br _x active layer. More importantly, MXene modification is favorable to improve the wettability of perovskite precursor solution with enhanced grain size and crystallinity, thereby increasing the UV long-term stability of solar cells. This work provides a new paradigm toward alleviating the severe nonradiative recombination at the interface in the device whilst enhancing the long-term stability via the preferential crystallization process.

Minimizing non-radiative recombination losses in the state-of-the-art non-fullerene solar cells is of utmost importance in order to achieve power conversion efficiencies over 20% in the future. This review discusses methods to accurately quantify non-radiative voltage losses as well as the current understanding of their origin and empirical strategies for reducing them.

Abstract

Organic solar cells benefit from non-fullerene acceptors (NFA) due to their high absorption coefficients, tunable frontier energy levels, and optical gaps, as well as their relatively high luminescence quantum efficiencies as compared to fullerenes. Those merits result in high yields of charge generation at a low or negligible energetic offset at the donor/NFA heterojunction, with efficiencies over 19% achieved for single-junction devices. Pushing this value significantly over 20% requires an increase in open-circuit voltage, which is currently still well below the thermodynamic limit. This can only be achieved by reducing non-radiative recombination, and hereby increasing the electroluminescence quantum efficiency of the photo-active layer. Here, current understanding of the origin of non-radiative decay, as well as an accurate quantification of the associated voltage losses are summarized. Promising strategies for suppressing these losses are highlighted, with focus on new material design, optimization of donor–acceptor combination, and blend morphology. This review aims at guiding researchers in their quest to find future solar harvesting donor–acceptor blends, which combine a high yield of exciton dissociation with a high yield of radiative free carrier recombination and low voltage losses, hereby closing the efficiency gap with inorganic and perovskite photovoltaics.

A new small molecule donor, SM-mB, is synthesized into a (SM-mB:L8-BO:Y6) ternary all-small molecule organic solar cell with alloyed acceptors composed of L8-BO and Y6, achieving the optimal PCE of 17.06%, which is attributed to the formation of hierarchical morphology induced by annealing treatment, greatly promoting exciton dissociation and charge transport, and improving the photovoltaic performance of devices.

Abstract

Achieving an ideal morphology to realize efficient charge generation and transport is an imperative avenue to improve the photovoltaic performance of all small-molecule organic solar cells (SM-OSCs). Here, ternary SM-OSCs are fabricated based on a new small molecule donor, SM-mB, and an alloyed blend acceptor of Y6 and its derivative, L8-BO, and desirable hierarchical morphology with appropriate nanoscale phase separation is successfully realized through adjusting the thermal annealing treatment conditions and compositions of mixed acceptors in the active layer. Then the ternary SM-OSCs achieve an excellent PCE of 17.06 %, which is one of the best results for the SM-OSCs so far. The desirable morphology can be ascribed to the optimization of the miscibility-driven donor and acceptor blend morphology that takes full advantage of the individual advantages of both acceptors, which facilitate efficient charge generation and extraction with more balanced charge carrier mobilities. More importantly, the photovoltaic performance of the ternary SM-OSCs possesses a high tolerance to the device fabrication conditions, including thermal annealing treatment, and is insensitive to film thickness, which is beneficial for large-area manufacture and future practical applications.

This work provides an insightful understanding of the role of driving force in the overall device performance by performing systematic and detailed loss analyses for each relevant JV parameter in a series of nonfullerene-acceptor-based low-offset organic solar cell systems. The losses via each loss channel are analyzed in detail. In general, this work presents a path toward more efficient organic solar cells.

Abstract

Low-offset organic solar cell systems have attracted great interest since nonfullerene acceptors came into the picture. While numerous studies have focused on the charge generation process in these low-offset systems, only a few studies have focused on the details of each loss channel in the charge generation process and their impact on the overall device performance. Here, several nonfullerene acceptors are blended with the same polymer donor to form a series of low-offset organic solar cell systems where significant variation in device performance is observed. Through detailed analyses of loss pathways, it is found that: i) the donor:acceptor interfaces of PM6:Y6 and PM6:TPT10 are close to the optimum energetic condition, ii) energetics at the donor:acceptor interface are the most important factor to the overall device performance, iii) exciton dissociation yield can be field-dependent owing to the sufficiently small energetic offset at the donor:acceptor interface, and iv) the change in substituents in the terminal group of Y-series acceptors in this work mainly affects energetics at the donor:acceptor interface instead of the interface density in the active layer. In general, this work presents a path toward more efficient organic solar cells.

Herein, the electron transfer/injection efficiency of the device is effectively improved by using Anth-hpp2 as the connecting layer between the PCBM and the electrode. The power conversion efficiency of the Anth-hpp2-based device is improved from 15.67% to 20.37%. The stabilities of the perovskite solar cells efficiency with Anth-hpp2 decay by only 5% after fabrication for about 2500 h.

Metal halide hybrid perovskite solar cells have recently emerged as a highly cost-effective photovoltaic technology. The cathode interlayer plays a critical role in aligning energy levels and promoting charge extraction in inverted perovskite solar cells. Herein, a novel multinitrogen derivative interlayer, Anth-hpp2, is designed and synthesized consisting of 1,1'-(4-(9,10-di(naphthalen-2-yl)anthracen-2-yl)pyridine-2,6-diyl)bis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a] pyrimidine), between the PCBM and top Ag electrode. The superbase group in Anth-hpp2 effectively contacts the silver electrode, reducing the work function of Ag. Consequently, the power conversion efficiency of the Anth-hpp2-based device improved from 16.05% to 20.37%, along with enhancements in short-circuit current and fill factor. The stabilities of perovskite solar cells are measured with Anth-hpp2 under N₂ storage, and the device efficiency with Anth-hpp2 decayed by only 5% after fabrication for approximately 2500 h, which is five times that of the control device. This study provides original insights into designing new cathode interlayer materials.

The performance of inverted perovskite solar cells is enhanced due to: (1) Amino groups in 4-butanediol ammonium Bromide (BD) react with the disassortative lead ion and fill formamidinium ions vacancies in perovskite, resulting in enhanced perovskite crystallinity; (2) The formation of hydrogen bonds between poly [bis (4-phenyl) (2,4,6-triMethylphenyl) amine](PTAA) and BD molecules contributes to the improved surface contact of PTAA/perovskite.

Abstract

Inverted perovskite solar cells (IPSCs) have witnessed an impressive development in recent years. However, their efficiency is still significantly behind theoretical limits, and device instabilities hinder their commercialization. Two main obstacles to further enhancing their performance via one-step deposition are: 1) the unsatisfactory film quality of perovskite and 2) the poor surface contact. To address the above issues, 4-butanediol ammonium Bromide (BD) is utilized to passivate Pb²⁺ defects by forming PbN bonds and fill vacancies of formamidinium ions at the buried surface of perovskite. The wettability of poly [bis (4-phenyl) (2,4,6-triMethylphenyl) amine] films is also improved due to the formation of hydrogen bonds between PTAA and BD molecules, resulting in better surface contacts and enhanced perovskite crystallinity. As a result, BD-modified perovskite thin films show a significant increase in the mean grain size, as well as a dramatic enhancement in the PL decay lifetime. The BD-treated device exhibits an efficiency of up to 21.26%, considerably higher than the control device. Moreover, the modified devices show dramatically enhanced thermal and ambient stability compared to the control ones. This methodology paves the way to obtain high-quality perovskite films for fabricating high-performance IPSCs.

The key role of methylammonium chloride additive in directing the crystallization of 1.8 eV perovskites to induce more effective halide homogenization is elucidated. The as-formed perovskite demonstrates suppressed halide segregation, improved optoelectronic properties, and ambient stability. In conjunction with a self-assembled monolayer (Me-4PACz), a V _OC of 1.25 V and steady-state PCE of 17% are achieved.

Abstract

Metal halide perovskite based tandem solar cells are promising to achieve power conversion efficiency beyond the theoretical limit of their single-junction counterparts. However, overcoming the significant open-circuit voltage deficit present in wide-bandgap perovskite solar cells remains a major hurdle for realizing efficient and stable perovskite tandem cells. Here, a holistic approach to overcoming challenges in 1.8 eV perovskite solar cells is reported by engineering the perovskite crystallization pathway by means of chloride additives. In conjunction with employing a self-assembled monolayer as the hole-transport layer, an open-circuit voltage of 1.25 V and a power conversion efficiency of 17.0% are achieved. The key role of methylammonium chloride addition is elucidated in facilitating the growth of a chloride-rich intermediate phase that directs crystallization of the desired cubic perovskite phase and induces more effective halide homogenization. The as-formed 1.8 eV perovskite demonstrates suppressed halide segregation and improved optoelectronic properties.

A novel spiro-type hole transport material (HTM) was developed by extending the π-conjugated system (DP). The new HTM features a stabilized HOMO level, a higher glass transition temperature, and improved morphology on the perovskite layer compared to spiro-OMeTAD. When incorporated into an n-i-p device, the DP-based HTM achieved a remarkable power conversion efficiency of 25.24 % for small-area devices and 21.86 % for modules.

Abstract

Hole transport materials (HTMs) are a key component of perovskite solar cells (PSCs). The small molecular 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl)-amine-9,9′-spirobifluorene (spiro-OMeTAD, termed “Spiro”) is the most successful HTM used in PSCs, but its versatility is imperfect. To improve its performance, we developed a novel spiro-type HTM (termed “DP”) by substituting four anisole units on Spiro with 4-methoxybiphenyl moieties. By extending the π-conjugation of Spiro in this way, the HOMO level of the HTM matches well with the perovskite valence band, enhancing hole mobility and increasing the glass transition temperature. DP-based PSC achieves high power conversion efficiencies (PCEs) of 25.24 % for small-area (0.06 cm²) devices and 21.86 % for modules (designated area of 27.56 cm²), along with the certified efficiency of 21.78 % on a designated area of 27.86 cm². The encapsulated DP-based devices maintain 95.1 % of the initial performance under ISOS-L-1 conditions after 2560 hours and 87 % at the ISOS-L-3 conditions over 600 hours.

Novel multifunctional polyoxometalate-based metal–organic framework (POMOF) with enhanced conductivity and charge mobility is assembled for integrating with perovskite solar cells (PSCs) to minimize deep-level defects and induce crystallization of oriented large-grained perovskite. Abundant phosphate groups endow POMOF with great advantages of in situ chemical anchoring and adsorption capacities to prevent toxic lead leakage, conducive to reducing environmental risks and developing eco-friendly PSCs.

Abstract

Despite the unprecedented progress in lead-based perovskite solar cells (PSCs), the toxicity and leakage of lead from degraded PSCs triggered by deep-level defects and poor crystallization quality increase environmental risk and become a critical challenge for eco-friendly PSCs. Here, a novel 2D polyoxometalate (POM)-based metal–organic framework (MOF) (C₅NH₅)₄(C₃N₂H₅)₂Zn₃(H₈P₄Mo₆O₃₁)₂·2H₂O (POMOF) is ingeniously devised to address these issues. Note that the integration of POM endows POMOF with great advantages of electrical conductivity and charge mobility. Ordered POMOF induces the crystallization of high-quality perovskite film and eliminates lead-based defects to improve internal stability. The resultant PSCs achieve a superior power conversion efficiency (23.3%) accompanied by improved stability that maintains ≈90% of its original efficiency after 1600 h. Meanwhile, POMOF with phosphate groups effectively prevents lead leakage through in situ chemical anchoring and adsorption methods to reduce environmental risk. This work provides an effective strategy to minimize lead-based defects and leakage in sustainable PSCs through multi-functional POM-based MOF material.

Cross-linked polyurethane (CLPU) obtained by quaternization process has an excellent water-resistant ability and high mechanical properties. As an interface layer, CLPU layer cannot only effectively induce secondary crystallization and passivate the surface defects of perovskite, reduce the non-radiative recombination, but also effectively block the moisture invasion. Therefore, the power conversion efficiency and stability of the prepared device are obviously improved.

Abstract

In the past decade, perovskite solar cells (PSCs) have made remarkable progress in improving power conversion efficiency (PCE). In order to further improve the photovoltaic performance and long-term stability of PSCs, the interface layer is essential. A multifunctional cross-linked polyurethane (CLPU) is designed and synthesized via the spontaneous quaternization of polyurethane and 1, 6-diiodohexane on the surface of the perovskite layer. CLPU layer cannot only effectively induce secondary crystallization and passivate the surface defects of perovskite, reduce the non-radiative recombination, but also effectively block the moisture invasion. By this strategy, Cs_0.05FA_0.95PbI₃ PSCs with excellent reproducibility, is realized, achieving a PCE of 23.14% with an open-circuit voltage of 1.11 V, a short-circuit current density of 25.69 mA cm⁻², and a fill factor of 0.81. In addition, the unencapsulated devices show enhanced stability in 35 ± 5% relative humidity (RH) near 3000 h and in 65 ± 5% RH over 700 h. This study provides valuable insights into the role of CLPU interface layer in PSCs, which are essential for the design of high-performance devices.

Publication date: 21 June 2023

Source: Joule, Volume 7, Issue 6

Author(s): Zhuoxin Li, Xing Li, Xianggang Chen, Xiaoxia Cui, Chunlin Guo, Xuzheng Feng, Dongxu Ren, Yaqi Mo, Miao Yang, Huiwei Huang, Rui Jia, Xuepeng Liu, Liyuan Han, Songyuan Dai, Molang Cai

A molecular synergistic passivation strategy is developed to engineer the buried interface for achieving efficient perovskite-based solar cells and self-powered photodetectors.

Abstract

The interface between the perovskite and electron-transporting material is often treated for defect passivation to improve the photovoltaic performance of devices. A facile 4-Acetamidobenzoic acid (containing an acetamido, a carboxyl, and a benzene ring)-based molecular synergistic passivation (MSP) strategy is developed here to engineer the SnO_x/perovskite interface, in which dense SnO_x are prepared using an E-beam evaporation technology while the perovskite is deposited with vacuum flash evaporation deposition method. MSP engineering can synergistically passivate defects at the SnO_x/perovskite interface by coordinating with Sn⁴⁺ and Pb²⁺ with functional group CO in the acetamido and carboxyl. The optimized solar cell devices can achieve the highest efficiency of 22.51% based on E-Beam deposited SnO_x and 23.29% based on solution-processed SnO₂, respectively, accompanied by excellent stability exceeding 3000 h. Further, the self-powered photodetectors exhibit a remarkably low dark current of 5.22 × 10⁻⁹ A cm⁻², a response of 0.53 A W⁻¹ at zero bias, a detection limit of 1.3 × 10¹³ Jones, and a linear dynamic range up to 80.4 dB. This work proposes a molecular synergistic passivation strategy to enhance the efficiency and responsivity of solar cells and self-powered photodetectors.

Two conjugated polyelectrolytes of PIIDNDI-Br and PDPPNDI-Br are designed via direct arylation polycondensation. The A1-A2 conjugated backbone ensures good charge-transporting properties and high conductivity, whereas distinct self-doping effect are observed for different acceptor combination. The PDPPNDI-Br and PIIDNDI-Br-based organic solar cells exhibit high power conversion efficiencies of 18.32% and 18.36%. Such dual-acceptor strategy of electron transport layers is efficient for thickness-insensitive and high-performance photovoltaic devices.

Abstract

The electron transport layer (ETL) is a critical component in achieving high device performance and stability in organic solar cells. Conjugated polyelectrolytes (CPEs) have become an attractive alternative due to film-forming properties and ease of preparation. However, p-type CPEs generally exhibit poor charge mobility and conductivity, incorporation of electron-withdrawing units forming alternated D-A conjugated backbone can make up for these deficiencies. Herein, the ratio of electron withdrawing moieties are further increased and two poly(A1-alt-A2) typed PIIDNDI-Br and PDPPNDI-Br based on the combination of naphthalene diimide (NDI) with isoindigo (IID) or diketopyrrolopyrrole (DPP) via direct arylation polycondensation are synthesized. These CPEs possess excellent alcohol solubility, a suitable lowest unocuppied molecular orbital energy level, and work function tunability. Surprisingly, the incorporation of IID and DPP units generate distinct self-doping behaviors, which are confirmed by UV–vis absorption and ESR spectra. However, no matter doped or undoped, both CPEs present better charge-transporting properties and conductivity when utilized as ETLs. The PIIDNDI-Br and PDPPNDI-Br display good universal compatibility with the blend of PM6:Y6 and PM6:L8-BO, and PCEs of 18.32% and 18.36% are obtained, respectively, which also present excellent storage stability. In short, the combination of two different acceptors demonstrates an efficient strategy to design highly efficient ETLs for high performance photovoltaic devices.

A novel semitransparent organic solar cell constructed by longitudinal through-hole strategy is proposed to eliminate the dependence of transparent devices on ultrathin active layer and electrode and applied into thick-film devices with record-breaking light utilization efficiency, which greatly expands the printing process window. Additionally, through-hole allows the organic materials to deform slightly and disperse extrusion stresses, thus exhibiting excellent flexural endurance.

Abstract

Semi-transparent organic solar cells (ST-OSCs) have great potential for application in vehicle- or building-integrated solar energy harvesting. Ultrathin active layers and electrodes are typically utilized to guarantee high power conversion efficiency (PCE) and high average visible transmittance (AVT) simultaneously; however, such ultrathin parts are unsuitable for industrial high-throughput manufacturing. In this study, ST-OSCs are fabricated using a longitudinal through-hole architecture to achieve functional region division and to eliminate the dependence on ultrathin films. A complete circuit that vertically corresponds to the silver grid is responsible for obtaining high PCE, and the longitudinal through-holes embedded in it allow most of the light to pass through,where the overall transparency is associated with the through-hole specification rather than the thicknesses of active layer and electrode. Excellent photovoltaic performance over a wide range of transparency (9.80–60.03%), with PCEs ranging from 6.04% to 15.34% is achieved. More critically, this architecture allows printable 300-nm-thick devices to achieve a record-breaking light utilization efficiency (LUE) of 3.25%, and enables flexible ST-OSCs to exhibit better flexural endurance by dispersing the extrusion stress into the through-holes. This study paves the way for fabricating high-performance ST-OSCs and shows great promise for the commercialization of organic photovoltaics.