Chen Weijie

Two commercialized solid additives thieno[3,2-b]thiophene (TT) and 3,6-dibromothieno[3,2-b]thiophene (TTB) are used to delicately regulate the blend film packing and crystallinity. High efficiencies of 17.75% with impressive thermal stability (T80 > 2800 h, 65 °C) and excellent photostability are achieved for TT-treated PM6:Y6 devices and a significantly higher PCE of 18.3% is achieved employing D18:L8-BO.

Abstract

Delicately manipulating nanomorphology is recognized as a vital and effective approach to enhancing the performance and stability of organic solar cells (OSCs). However, the complete removal of solvent additives with high boiling points is typically necessary to maintain the operational stability of the device. In this study, two commercially available organic intermediates, namely thieno[3,2-b]thiophene (TT) and 3,6-dibromothieno[3,2-b]thiophene (TTB) are introduced, as solid additives in OSCs. The theoretical simulations and experimental results indicate that TT and TTB may exhibit stronger intermolecular interactions with the acceptor Y6 and donor PM6, respectively. This suggests that the solid additives (SAs) can selectively intercalate between Y6 and PM6 molecules, thereby improving the packing order and crystallinity. As a result, the TT-treated PM6:Y6 system exhibits a favorable morphology, improved charge carrier mobility, and minimal charge recombination loss. These characteristics contribute to an impressive efficiency of 17.75%. Furthermore, the system demonstrates exceptional thermal stability (T ₈₀ > 2800 h at 65 °C) and outstanding photostability. The universal applicability of TT treatment is confirmed in OSCs employing D18:L8-BO, achieving a significantly higher PCE of 18.3%. These findings underscore the importance of using appropriate solid additives to optimize the blend morphology of OSCs, thereby improving photovoltaic performance and thermal stability.

Herein, a successful design strategy of medium-bandgap polymer acceptor, PYFO-V, is presented for indoor all-polymer solar cell operation. By the synergy of alkoxy chains and vinylene spacers onto Y-series polymer acceptors, PYFO-V exhibits blue-shifted absorption and upshifted energy levels. The binary devices realize an impressive efficiency of 27.1% under indoor illumination with great photostability, beneficial for the Internet-of-Things application.

Abstract

Indoor photovoltaics (IPVs) are garnering increasing attention from both the academic and industrial communities due to the pressing demand of the ecosystem of Internet-of-Things. All-polymer solar cells (all-PSCs), emerging as a sub-type of organic photovoltaics, with the merits of great film-forming properties, remarkable morphological and light stability, hold great promise to simultaneously achieve high efficiency and long-term operation in IPV's application. However, the dearth of polymer acceptors with medium-bandgap has impeded the rapid development of indoor all-PSCs. Herein, a highly efficient medium-bandgap polymer acceptor (PYFO-V) is reported through the synergistic effects of side chain engineering and linkage modulation and applied for indoor all-PSCs operation. As a result, the PM6:PYFO-V-based indoor all-PSC yields the highest efficiency of 27.1% under LED light condition, marking the highest value for reported binary indoor all-PSCs to date. More importantly, the blade-coated devices using non-halogenated solvent (o-xylene) maintain an efficiency of over 23%, demonstrating the potential for industry-scale fabrication. This work not only highlights the importance of fine-tuning intramolecular charge transfer effect and intrachain coplanarity in developing high-performance medium-bandgap polymer acceptors but also provides a highly efficient strategy for indoor all-PSC application.

Designing narrow band gap acceptors with high PLQY and strong crystallinity can effectively reduce non-radiative energy losses and enhance OSC performance. We synthesized DM-F, an A–D–A fused-ring acceptor, which hinders H-aggregate formation, boosts PLQY, and shows strong near-infrared absorption and crystallinity. DM-F-based OSCs exhibit low ▵E _nr (0.14 eV) and high PCE, reaching 16.16 % and 20.09 % in binary and ternary cells, respectively.

Abstract

Designing and synthesizing narrow band gap acceptors that exhibit high photoluminescence quantum yield (PLQY) and strong crystallinity is a highly effective, yet challenging, approach to reducing non-radiative energy losses (▵E _nr) and boosting the performance of organic solar cells (OSCs). We have successfully designed and synthesized an A–D–A type fused-ring electron acceptor, named DM-F, which features a planar molecular backbone adorned with bulky three-dimensional camphane side groups at its central core. These bulky substituents effectively hinder the formation of H-aggregates of the acceptors, promoting the formation of more J-aggregates and notably elevating the PLQY of the acceptor in the film. As anticipated, DM-F showcases pronounced near-infrared absorption coupled with impressive crystallinity. Organic solar cells (OSCs) leveraging DM-F exhibit a high EQE_EL value and remarkably low ▵E _nr of 0.14 eV-currently the most minimal reported value for OSCs. Moreover, the power conversion efficiency (PCE) of binary and ternary OSCs utilizing DM-F has reached 16.16 % and 20.09 %, respectively, marking a new apex in reported efficiency within the OSCs field. In conclusion, our study reveals that designing narrow band gap acceptors with high PLQY is an effective way to reduce ▵E _nr and improve the PCE of OSCs.

Publication date: August 2024

Source: Nano Energy, Volume 127

Author(s): Hatameh Asgarimoghaddam, Qiaoyun Chen, Fan Ye, Ahmed Shahin, Olivia Alexandra Celeste Marchione, Bo Song, Kevin Philip Musselman

In-Situ Self-Assembly Dipole Shielding Layer strategy allows to experimentally alleviate the unexpected surface defects and suppress the spontaneous non-radiative recombination by means of regulating the dipole moment length and Van der Waals gap. Consequently, the as-fabricated CsPbI_2.75Br_0.25 perovskite solar cells demonstrate 19.77% PCE whilst superior long-term stability.

Abstract

Despite CsPbI_2.75Br_0.25 inorganic perovskites exhibit high potential for single-junction and/or tandem solar cells, unexpected non-radiative recombination, and mismatched interfacial band alignment within the inorganic perovskite solar cells (PSCs) disadvantageously affect their photovoltaic performance. Rational design of the dipole shielding layer (DSL) is vital to realize a win–win situation for the defect passivation and band alignment. Herein, A-site dipole molecules, that is, neopentylamine and 2-methylbutylamine, are employed for in-situ self-assembly of a thus-far unreported DSL at the interface between 3D perovskite and hole transport layer. The as-prepared DSL demonstrates a 2D RP phase perovskite and the lattice-matching structurally-stable DSL@3D perovskite enables to alleviate the unexpected surface defects and suppress the spontaneous non-radiative recombination by means of effectively tuning the surface work function via regulating the dipole moment length and Van der Waals gap. Accordingly, the top dipole-modified inorganic PSCs exhibit a champion power conversion efficiency (PSC) as high as 19.77% and a fill factor over 83%. Equally importantly, the corresponding solar cells demonstrate a remarkable enhanced stability, maintaining 90% of its initial efficiency for more than 1200 h without encapsulation under a 20% ± 5% relative humidity.

This study investigates the effect of DGEBA and DMSO on PEDOT:PSS, and utilized in perovskite solar cells. DGEBA induces grain size growth and imparts hydrophobicity, protecting the perovskite layer from moisture. Meanwhile, DMSO enhances conductivity by separating PSS groups. The perovskite solar cell using modified PEDOT:PSS improves the power conversion efficiency with improved stability under heat and light-induced conditions.

Abstract

Poly(3,4-ethylenedioxythiophene) (PEDOT), particularly in its complex form with poly(styrene sulfonate) (PEDOT:PSS), stands out as a prominent example of an organic conductor. Renowned for its exceptional conductivity, substantial light transmissibility, water processability, and remarkable flexibility, PEDOT:PSS has earned its reputation as a leading conductive polymer. This study explores the unique effects of two additives, Bisphenol A diglycidyl ether (DGEBA) and Dimethyl sulfoxide (DMSO), on the PSS component of PEDOT:PSS films are shown. Both additives induce grain size growth, while DGEBA makes the PEDOT:PSS layer hydrophobic, which acts as a passivation to protect the perovskite layer, which is vulnerable to moisture. The other additive, DMSO, separates the PSS groups, resulting in increased conductivity through the free movement of holes. With these multi-modified p-type PEDOT:PSS, the ITO/M-PEDOT:PSS/Perovskite/PCBM/Ag structured reverse structure solar cell has improved the power conversion efficiency (PCE) from 15.28% to 17.80% compared to the control cell with conventional PEDOT:PSS. It also maintains 90% for 500 h at 60 °C and 300 h at 1 sun illuminating conditions.

We demonstrate that the lead-chelating intermediate phase promotes the formation of α-FAPbI₃ at ambient air, bypassing the formation of δ-FAPbI₃. The crystallinity of perovskites and the α-phase stability are remarkably improved. Consequently, the ambient-fabricated FAPbI₃ perovskite solar cells exhibit an outstanding power conversion efficiency of 25.08 %, along with the high open-circuit voltage (1.19 V).

Abstract

Formamidinium-lead triiodide (FAPbI₃) perovskite holds promise as a prime candidate in the realm of perovskite photovoltaics. However, the photo-active α-FAPbI₃ phase, existing as a metastable state, is observable solely at elevated temperatures and is susceptible to degradation into the δ-phase in ambient air. Therefore, the attainment of phase-stable α-FAPbI₃ in ambient conditions has become a crucial objective in perovskite research. Here, we proposed an efficient conversion process of PbI₂ into the α-FAPbI₃ perovskites in ambient air. This conversion was facilitated by the introduction of chelating molecules, which interacted with PbI₂ to form an intermediate phase. Due to the reduced formation barrier resulting from the altered reaction pathway, this stable intermediate phase transitioned directly into α-FAPbI₃ upon the deposition of the organic cation solution, effectively bypassing the formation of δ-FAPbI₃. Consequently, the ambient-fabricated FAPbI₃ perovskite solar cells (PSCs) exhibited an outstanding power conversion efficiency of 25.08 %, along with a high open-circuit voltage of 1.19 V. Furthermore, the unencapsulated devices demonstrated remarkable environmental stability. Notably, this innovative approach promises broad applicability across various chelating molecules, opening new avenues for further progress in the ambient air fabrication of FAPbI₃ PSCs.

Novel tetrasubstituted paracyclophanes as hole transport materials for organic metal halide perovskite solar cells are synthesized and their properties are investigated in-depth. By using MIS-CELIV characterization and density functional theory the charge carrier mobilities of the pristine and doped paracyclophane hole transport materials are investigated and their properties and thermal stability are qualified in methylammonium lead iodide solar cells.

Abstract

Because of its excellent hole conductivity, p-doped 2,2′7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9′-spiro-bifluorene (spiro-MeOTAD) is commonly deployed for hole transport in organic metal halide perovskite solar cells, but its rather expensive synthesis prompts the research for alternatives. In this work, tetrasubstituted [2.2]paracyclophanes (PCPs) are synthesized and investigated for replacing spiro-MeOTAD. To enhance their conductivity, different doping strategies are followed. Best conductivities are achieved by doping PCP thin films with tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III) tris(bis(trifluoromethylsulfonyl)imide) (FK209), matching the conductivity of state-of-the-art p-doped spiro-MeOTAD. Best performance in solar cells is leveraged by doping PCPs with the co-dopants lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 4-tert-butylpyridine (tBP) which are also used to p-dope spiro-MeOTAD thin films in solar cells. Yet, the thermal device stability is maximized upon doping PCPs with FK209 and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄TCNQ).

Publication date: August 2024

Source: Nano Energy, Volume 127

Author(s): Qianyu Liu, Zeping Ou, Zhu Ma, Zhangfeng Huang, Yanlin Li, Shanyue Hou, Jie Ren, Jin Peng, Lihong Bai, Hong Yu, Zhuo Lv, Yan Xiang, Jian Yu, Wenfeng Zhang, Fangdan Jiang, Kuan Sun, Tong Zhu, Liming Ding

Wide bandgap perovskites are promising candidates for indoor photovoltaics that can power the Internet of Things (IoT) devices. A bromide-rich bulk and surface 2D passivation strategy is developed to enhance the performance and phase stability of wide bandgap perovskites for indoor applications.

Indoor photovoltaics (IPV) is a promising technology to power the rapidly developing Internet of Things (IoT) devices, offering advantages of distributed power source and reduced maintenance cost. Wide-bandgap perovskite solar cells (PSCs), with the features of easy bandgap tuning and low-cost solution process, hold significant potential for powering indoor IoT devices. However, the efficiency and stability of wide-bandgap PSCs suffers from severe phase segregation and surface defects. Herein, a novel bromide-rich 2D passivation strategy targeting both bulk and surface passivation of wide-bandgap PSCs for IPV application is introduced. Ammonium salts with optimized alkyl chain length is confirmed to suppress the phase segregation in the bulk. Bromide-rich 2D perovskite exhibit superior performance compared to their iodide counterparts, effectively suppressing nonradiative recombination and forming favorable energy band alignment with the electron transport layer (ETL). The wide-bandgap PSCs achieved an impressive power conversion efficiency (PCE) up to 41.58% under 1000 lux light emitting diode (LED) illumination. Furthermore, the wide-bandgap perovskite module efficiently powers a Bluetooth IoT sensor at 400 lux indoor illumination, which can sense and broadcast the environmental information. This work highlights the remarkable potential of wide-bandgap PSCs for indoor IoT devices and provides valuable insights into enhancing the efficiency and stability of PSCs for future IoT applications.

Passivation of the top and bottom interfaces of perovskite layers using 1-(4-Fluorophenyl) biguanide hydrochloride (F-BHCl) in inverted perovskite solar cells (PSC). The power conversion efficiency of PSC after the modification of double interfaces with F-BHCl is significantly increased from 22.41% (unmodified) to 25.14%.

Abstract

The improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSC) relies on the enhanced quality of perovskite layer and the modification of its adjacent interfaces. For this purpose, a multifunctional organic passivation molecule 1-(4-Fluorophenyl) biguanide hydrochloride (F-BHCl) is introduced to the top and bottom interfaces of the perovskite layer. The PCE of PSC after the modification of double interfaces with F-BHCl is significantly increased from 22.41% (unmodified) to 25.14%, and the storage, thermal, and operation stability is also improved. The comprehensive theoretical and experimental studies verify that due to its versatile functional groups and adaptation, F-BHCl can significantly improve the quality of perovskite film, fully passivate several kinds of common defects, smoothen the top surfaces of perovskite film, and construct “molecular bridges” with carrier transporters on both the top and bottom surfaces, leading to significantly reduced non-recombination and carrier transport losses. As a result, a significant increase is achieved in the open circuit voltage and fill factor as well as the whole performance of the device.

The 2-methylpiperazinium bromide (2-MePBr) is employed to treat the surface of wide-bandgap (1.77 eV) perovskites to inhibit the ion migration and passivate defects. The 2-MePBr treatment has resulted in an improved power conversion efficiency of 19.30% with a V _OC of 1.29 V and a remarkable fill factor of 83.08%, as well as enhanced stability.

Abstract

Wide-bandgap (WBG) perovskite solar cell (PSC) plays a pivotal role as the top subcell in all-perovskite tandem solar cells (TSCs), facilitating the absorption of high-energy photons and affording a large open-circuit voltage (V _OC). Nonetheless, the stability and efficiency of WBG PSCs are constrained by light-induced halide segregation and non-radiative recombination losses. In this study, this work presents an approach of utilizing 2-methylpiperazinium bromide (2-MePBr) via interfacial engineering to realize high-efficiency WBG (1.77 eV) PSCs. The C─NH─C functional group in 2-MePBr, serving as an electron donor, can interact with under-coordinated lead defects at the perovskite surface. Consequently, the treatment with 2-MePBr mitigates interfacial non-radiative recombination, enhances charge transport, inhibits ion migration, and thus delivers an improved power conversion efficiency (PCE) of 19.30% with a V _OC of 1.29 V, and a fill factor of 83.08%. Notably, the WBG PSCs manifest enhanced stability, preserving 80% of the initial PCE after 337 h of continuous operation under 1 sun illumination at the maximum power point. Furthermore, the all-perovskite TSCs based on this WBG subcell achieve a PCE of 27.47%, showing its promising application in perovskite-based tandem solar cells.

An approach is proposed to modify perovskite surface utilizing mixed solvents and metallocene materials. The mixed solvent efficiently exposes trap defects on the perovskite surface, while the high electronegativity metallocene material effectively passivates these defects, significantly enhancing carrier transport efficiency. A certified PCE exceeding 30% is obtain on perovskite/silicon tandem solar cells.

Abstract

The presence of a high density of defects at the perovskite/electron transport layer (ETL) interface results in significant nonradiative recombination losses, thus impeding the efficiency enhancement of perovskite/silicon tandem solar cells (TSCs). In this investigation, a metallocene-based molecule, cobalt (III) dichlorophene hexafluorophosphate (CcPF₆), is employed for perovskite surface passivation. To maximize its efficacy, the molecule is dissolved in a mixed solvent of acetonitrile and chlorobenzene, leading to the reconstruction of the perovskite surface and effective passivation of surface defects. This modification strategy substantially enhances the overall efficiency of perovskite/silicon tandem solar cells by mitigating the issue of low fill factor resulting from non-uniform coating of the top perovskite layer on the textured silicon bottom cell. Leveraging a double-sided textured silicon heterojunction (HJT) bottom cell, a certified power conversion efficiency (PCE) of 30.43% for a monolithic perovskite/silicon TSC (1.00 cm²) is achieved, featuring an open-circuit voltage (V _oc) of 1.93 V and a fill factor (FF) of 78.43%. After storage in the drying cabinet (5% humidity at 20 °C) for 1000 h, the device retains 94.27% of its initial performance.

A facile strategy incorporating AlO_x deposited by controlled growth was developed to modulate the perovskite surface. The infiltrated Al³⁺ can suppress ion migration and phase separation, regulate the arrangement of energy levels, and passivate defects on the perovskite surface and grain boundaries. A monolithic perovskite-silicon tandem solar cell achieved a PCE of 28.50 % with excellent photothermal stability.

Abstract

Inverted perovskite solar cells (PSCs) are preferred for tandem applications due to their superior compatibility with diverse bottom solar cells. However, the solution processing and low formation energy of perovskites inevitably lead to numerous defects at both the bulk and interfaces. We report a facile and effective strategy for precisely modulating the perovskite by incorporating AlO_x deposited by atomic layer deposition (ALD) on the top interface. We find that Al³⁺ can not only infiltrate the bulk phase and interact with halide ions to suppress ion migration and phase separation but also regulate the arrangement of energy levels and passivate defects on the perovskite surface and grain boundaries. Additionally, ALD-AlO_x exhibits an encapsulation effect through a dense interlayer. Consequently, the ALD-AlO_x treatment can significantly improve the power conversion efficiency (PCE) to 21.80 % for 1.66 electron volt (eV) PSCs. A monolithic perovskite-silicon TSCs using AlO_x-modified perovskite achieved a PCE of 28.5 % with excellent photothermal stability. More importantly, the resulting 1.55 eV PSC and module achieved a PCE of 25.08 % (0.04 cm²) and 21.01 % (aperture area of 15.5 cm²), respectively. Our study provides an effective way to efficient and stable wide-band gap perovskite for perovskite-silicon TSCs and paves the way for large-area inverted PSCs.

To enhance interface bonding and charge transfer in perovskite solar cells, halogenated spiro[fluorene-9,9’-xanthene]-based molecules are designed as interfacial layers, structurally similar to charge selective contacts. The halogenated interlayers passivate defects, optimize energy level alignment, and stabilize interface contact, resulting in enhanced efficiency and stability. This work offers a novel approach toward high-efficiency and durable photovoltaic devices.

Abstract

Weak bonding between the perovskite and charge transport layers can lead to interfacial defects, hindering charge transfer and limiting the efficiency and stability of perovskite solar cells (PSCs). To address this issue, two halogenated spiro[fluorene-9,9′-xanthene]-based molecules (SFX-DM-F and SFX-DM-Cl) are designed as an interfacial layer between perovskite and hole transport materials (HTMs). Both first-principles simulations and experimental results are used to demonstrate that these halogenated interfacial layers improve the contact stability between perovskite's Pb(II) and HTMs, increasing the efficiency of charge transfer. The similar structure of interlayer to HTM also enhances the interfacial hole transfer integral, favoring effective hole transport. The PSCs based on SFX-DM-Cl achieve power conversion efficiencies of 24.8% (0.0625 cm²) and 23.1% (1 cm²). Even after 2000 h at a relative humidity of 15–20%, the unencapsulated PSC retains 94% of its initial efficiency. This work proposes the halogenated homologous HTMs as interfacial molecular bridges to optimize weak chemical bonds and hole transfer, thereby enabling efficient and stable PSCs.

A bilayer electron-transport-materials (ETMs) strategy consisting of an indium-doped ZnO (IZO) and a pristine ZnO to fabricate ultrathin flexible organic solar cells (OSCs) is developed. The device prepared based on the gradient bilayer ETMs can achieve a power conversion efficiency of 16.1%, which is the highest efficiency for ultrathin (less than 10 μm) flexible OSCs based on the solution-processed electrodes.

Ultrathin flexible organic solar cells (OSCs) have garnered widespread attention in wearable electronic devices for their lightweight and excellent conformability. Silver nanowires (AgNWs) are one of the most widely used bottom electrodes because of their high conductivity and transmittance. However, the high roughness of AgNWs on the flexible substrate exerts adverse effects on device performance. To address this critical issue, a bilayer electron-transport-materials (ETMs) strategy consisting of an indium-doped zinc oxide (IZO) and a pristine ZnO is developed. The IZO is utilized as the first layer of ETM, which can effectively fill voids in AgNWs to form a high-conductive composite electrode. The ZnO is used as the second layer of ETM, facilitating charge extraction. The ultrathin flexible OSCs prepared based on the gradient bilayer ETMs can achieve a power conversion efficiency (PCE) of 16.1%, associated with improved mechanical stability, showing a PCE retention of 93% after 10 000 bending cycles (R = 1 mm) and 82% under 1000 compression (30%)-release cycling test. To the best of knowledge, it's one of the highest efficiency for ultrathin (less than 10 μm) flexible OSCs based on the solution-processed electrodes. This work will provide a new avenue for fabricating high-performance and mechanically robust ultraflexible ITO-free OSCs.

This study investigates the crucial role of the physicochemical characteristics of the SnO₂ colloidal suspension in shaping the morphology, electrical properties, and optical properties of the SnO₂ electron transport layer (ETL). The acid-modified SnO₂ ETL exhibits advanced properties, resulting in perovskite solar cells (PSCs) with 24.70% power conversion efficiency (PCE) and good stability.

The commercial tin oxide (SnO₂) colloidal suspension is widely utilized as an electron transport layer (ETL) in high-performance perovskite solar cells (PSCs). However, despite significant efforts have been proposed to address bulk transport and interface recombination issues, the PSC efficiency is still limited to around 25%. In this study, the crucial role of the physicochemical characteristics of the SnO₂ colloidal suspension in shaping the morphology, electrical properties, and optical properties of the SnO₂ ETL is investigated. By controlling the pH value of the SnO₂ solution with weak acids such as carbonic acid, the reassembly of metal oxide nanoparticles into smaller sizes with more homogeneous dispersion and dense interconnections is successfully induced. Consequently, the resulting SnO₂ ETL exhibits enhanced crystallinity, high conductivity, low surface defects, and high optical transmittance. As a result, the efficiency of the target PSC is increased from 23.10% (control device) to 24.70%. This improvement is attributed to higher voltage, photocurrent, and fill factor compared to the relevant control samples. A similar device improvement using phosphoric acid is observed, indicating that the approach represents a universal technique to further enhance the quality of SnO₂ ETL for large-area, high-efficiency, and stable PSCs.

Liquid-type zwitterion (LTZ) is synthesized by combining the equimolar ratio of zwitterion and LiTFSI to adjust the intermolecular interactions of zwitterions. Employing LTZ on SnO₂ surface effectively suppresses zwitterion aggregation, resulting in uniform films, excellent electrical properties, and reduced recombination. Consequently, the LTZ-based perovskite solar cells attain power conversion efficiencies of 24.9% for small-area devices and 19.86% for modules, and improved long-term stability.

Abstract

Passivation of perovskite crystals is a crucial strategy to improve the efficiency and stability of perovskite solar cells (PSCs). Zwitterions, which contain both positive and negative charges in the molecule, can be used to passivate perovskite crystals. However, these materials strongly interact with each other, resulting in extremely low solubility in common organic solvents. The low solubility of zwitterions hinders the formation of uniform films, which negatively affects perovskite crystal growth. In this study, a liquid-type zwitterion (LTZ) is synthesized by modulating intermolecular interactions of the zwitterion (3-(1-Pyridinio)-1-propanesulfonate). By suppressing intermolecular interactions, the solubility and processibility of the zwitterion in common organic solvents are successfully improved. The well-distributed LTZ-treated films are obtained, resulting in better electrical properties for the PSCs compared to solid-type zwitterion-based devices. With these characteristics, the resulting device achieves a power conversion efficiency of 24.9% with excellent thermal stability (under 60 °C and N₂ atmosphere), maintaining over 80% of its initial efficiency for 1968 h. In addition, the PSC module (active area of 32.7 cm²) achieves an improved efficiency of 19.86% with high open-circuit voltage and fill factor. The results suggest that interface engineering with an LTZ has the potential to fabricate efficient and stable PSCs.

Transparent recombination layers for two-terminal perovskite-based tandem solar cells are reviewed, including their fundamental functions, photophysical mechanisms, working principles, requirements, and characterization methods. Existing challenges and future perspectives for research in this promising field are also presented.

Abstract

Two-terminal (2T) perovskite-based tandem solar cells (TSCs) arouse burgeoning interest in breaking the Shockley–Queisser (S–Q) limit of single-junction solar cells by combining two subcells with different bandgaps. However, the highest certified efficiency of 2T perovskite-based TSCs (33.9%) lags behind the theoretical limit (42–43%). A vital challenge limiting the development of 2T perovskite-based TSCs is the transparent recombination layers/interconnecting layers (RLs) design between two subcells. To improve the performance of 2T perovskite-based TSCs, RLs simultaneously fulfill the optical loss, contact resistance, carrier mobility, stress management, and conformal coverage requirements. In this review, the definition, functions, and requirements of RLs in 2T perovskite-based TSCs are presented. The insightful characterization methods applicable to RLs, which are inspiring for further research on the RLs both in 2T perovskite-based two-junction and multi-junction TSCs, are also highlighted. Finally, the key factors that currently limit the performance enhancement of RLs and the future directions that should be continuously focused on are summarized.

Publication date: September 2024

Source: Journal of Energy Chemistry, Volume 96

Author(s): Zhimin Fang, Ting Nie, Jianning Ding, Shengzhong (Frank) Liu

A series of dual-acceptor conjugated polymers (DPPF-BDD, DPPT-BDD, and DPPSe-BDD) comprising furan/thiophene/selenophene-flanked diketopyrrolopyrrole (DPP) and dioxo-benzodithiophene (BDD) as repeating units are synthesized and successfully incorporated into organic field-effect transistors (OFETs) as semiconductors and perovskite solar cells (PSCs) as a passivating material. New series of polymers display ambipolar OFET characteristics while PSCs display a high PCE (≈23%).

While dual-acceptor-type conjugated polymers have witnessed a great success in organic field-effect transistors (OFETs), their potential multifunctionality in other optoelectronic devices has been overlooked. Herein, three conjugated polymers (DPPF-BDD, DPPT-BDD, and DPPSe-BDD) comprising furan/thiophene/selenophene-flanked diketopyrrolopyrrole (DPP) and dioxo-benzodithiophene (BDD) as repeating units are designed, synthesized, and characterized. Modulating the chalcogen on DPP flank shows an impact on dual-acceptor polymer optoelectronic properties. Subsequently, the potential of these polymers in both OFETs and perovskite solar cells (PSCs) either as semiconductors or as passivation materials, respectively, is investigated. Interestingly, DPPF-BDD, DPPT-BDD, and DPPSe-BDD show ambipolar behavior in vacuum with hole (μ _h) and electron (μ _e) mobilities of 0.0263/0.0223, 0.0187/0.0123, and 0.0070/0.0051 cm² V⁻¹ s⁻¹, respectively. Upon doping tetrabutylammonium iodide into DPPF-BDD, DPPT-BDD, and DPPSe-BDD polymers, the respective OFETs show relatively higher μ _h and μ _e (0.0389/0.0503; 0.0289/0.0259; 0.0058/0.0156 cm² V⁻¹ s⁻¹) than the undoped polymer OFETs. Furthermore, DPPF-BDD-, DPPT-BDD-, and DPPSe-BDD-incorporated (in the antisolvent treatment and PCBM electron transport layer) PSCs display maximum power conversion efficiency of 23.48%, 22.85%, and 23.35%, respectively, surpassing the control device (22.83%), which is benefited from the perovskite surface passivation and the charge extraction improvement. Overall, a new class of multifunctional DPP-based dual-acceptor-type polymers that are highly compatible with OFETs and high-performance PSCs is presented.

The terminal groups of similar carbazole-based self-assembled molecules play a crucial role in determining the final power conversion efficiency in inverted perovskite solar cell devices. The morphology of the perovskite photoactive layer and the charge kinetics are influenced by the nature of the functional group.

Four different carbazole-based self-assembled molecules (SAMs) with different terminal groups have been designed and synthesized as hole-selective contacts for inverted perovskite solar cells to investigate their interfacial interactions and, consequently, the performance of the devices. Using the carbazole core as a reference, the effect of the thiophen-2-yl phenyl, or the hydroxymethyl phenyl attached to the core through a phenyl moiety, with that of the thiophene directly linked to the carbazole is compared. These new SAMs have been successfully synthesized using cost-effective starting materials and a straightforward synthetic method, eliminating the need for expensive and complex purification processes. Subsequently, they have been applied as efficient hole-selective contact in inverted perovskite solar cells, leading to an outstanding power conversion efficiency of 19.67% in the case of SAM5, containing a carbazole-core substituted with double 2-phenylthiophene side arms as functional group. The detailed characterization of the interface and the charge kinetics has allowed to determine the effect of each substituent.

A ligand-induced energy level modulation of perovskite quantum dots (PQDs) is reported for band engineering of PQD solids, which can form a gradient band structure within the PQD solids with substantially diminishes trap-assisted nonradiative recombination, significantly promoting the charge transport within the PQD solids. Consequently, the band-engineered PQD solar cells give a remarkable efficiency of up to 16.44%.

Abstract

CsPbI₃ perovskite quantum dot (PQD) shows high potential for next-generation photovoltaics due to their tunable surface chemistry, good solution-processability and unique photophysical properties. However, the remained long-chain ligand attached to the PQD surface significantly impedes the charge carrier transport within the PQD solids, thereby predominantly influencing the charge extraction of PQD solar cells (PQDSCs). Herein, a ligand-induced energy level modulation is reported for band engineering of PQD solids to improve the charge extraction of PQDSCs. Detailed theoretical calculations and systemic experimental studies are performed to comprehensively understand the photophysical properties of the PQD solids dominated by the surface ligands of PQDs. The results reveal that 4-nitrobenzenethiol and 4-methoxybenzenethiol molecules with different dipole moments can firmly anchor to the PQD surface through the thiol group to modulate the energy levels of PQDs, and a gradient band structure within the PQD solid is subsequently realized. Consequently, the band-engineered PQDSC delivers an efficiency of up to 16.44%, which is one of the highest efficiencies of CsPbI₃ PQDSCs. This work provides a feasible avenue for the band engineering of PQD solids by tuning the surface chemistry of PQDs for high-performing solar cells or other optoelectronic devices.

A series of efficient multi-component copolymerized donors (MCDs) P1_0.8/P2_0.2 , P1_0.8/P2_0.2-TCl, P1_0.7/P2_0.3-TCl, and P1_0.6/P2_0.4-TCl were synthesized, and excellent efficiencies in both rigid (18.53 %) and flexible (17.03 %) OSCs along with fracture strain in pristine film (16.59 %) for P1_0.8/P2_0.2-TCl were achieved.

Abstract

Multi-component copolymerized donors (MCDs) have gained significant interest and have been rapidly developed in flexible organic solar cells (f-OSCs) in recent years. However, ensuring the power conversion efficiency (PCE) of f-OSCs while retaining ideal mechanical properties remains an enormous challenge. The fracture strain (FS) value of typical high-efficiency blend films is generally less than 8 %, which is far from the application standards of wearable photovoltaic devices. Therefore, we developed a series of novel MCDs after meticulous molecular design. Among them, the consistent MCD backbone and end-capped functional group formed a highly conjugated molecular plane, and the solubilization and mechanical properties were effectively optimized by modifying the proportion of solubilized alkyl chains. Consequently, due to the formation of entangled structures with a frozen blend film morphology considerably improved the high ductility of the active layer, P1_0.8/P2_0.2-TCl exhibited efficient PCE in rigid (18.53 %) and flexible (17.03 %) OSCs, along with excellent FS values (16.59 %) in pristine films, meanwhile, the outstanding FS values of 25.18 % and 12.3 % were achieved by P1_0.6/P2_0.4-TCl -based pristine and blend films, respectively, which were one of the highest records achieved by end-capped MCD-based binary OSCs, demonstrating promising application to synchronize the realization of high-efficiency and mechanically ductile flexible OSCs.