Cathode Interfacial Layer Research Articles

All Roads Lead to Rome: Isomers with Divergent Cathode Modification Mechanisms toward Ohmic Contact.

Cathode interfacial layers (CILs) hold utmost importance for achieving ohmic contact at the organic semiconductor-cathode interface of organic photovoltaic devices. Delving deep into diverse design principles and working mechanisms is of great significance for designing novel CILs with high performance. Herein, two novel nonamine-based CILs are designed: one featuring a cyclopentadiene unit, designated as CIL-cp; while the other, lacking cyclopentadiene, is referred to as CIL-ph, which is an isomer of CIL-cp. The subtle changes in chemical structures result in distinct modification mechanisms toward ohmic contact. On one hand, the robust electron-withdrawing characteristic of cyclopentadiene endows CIL-cp with lower energy levels, resulting in an interfacial dipole at the active layer-CIL-cp interface due to electron transfer from D18 to CIL-cp. On the other hand, CIL-ph exhibits a strong interfacial dipole at the CIL-Ag interface, which significantly reduces the work function (WF) of the silver electrode. Both CIL-cp and CIL-ph demonstrate excellent interfacial modification capability, whereas CIL-cp possesses a stronger electron extraction ability, thus leading to a high power conversion efficiency of 19.31% in the D18:L8-BO system. Our results reveal the distinctive operational mechanism of cyclopentadiene-based CILs, thus offering innovative design ideas for CIL materials.

Glycolic acid doped PFN-Br as cathode interface to achieve high-efficiency in organic solar cells

Small compounds are often utilized to adjust the cathode interface of organic solar cells (OSCs) due to their low batch change, easy synthesis, unambiguous chemical structure, and low cost. In this work, the alcohol-soluble small molecule material Glycolic acid was doped into the electron transport material Poly(9, 9-bis(3′-(N, N-dimethyl)-N-ethylammoniumpropyl-2, 7-fluorene)-alt-2, 7-(9, 9-dioctylfluorene)) dibromide (PFN-Br) to modify the performance of the cathode interface layer (CIL). The CIL doped with Glycolic acid has better surface morphology, which is conducive to charge transport and extraction. In addition, the introduction of Glycolic acid improves the hydrophilicity of CIL, makes the metal electrode have good contact with CIL, and helps to improve the stability of the OSCs. Additionally, it suppresses the device's trap-assisted recombination and bimolecular recombination, hastening exciton dissociation and charge collection. As a result, the power conversion efficiency (PCE) of OSCs based on PM6: Y6 blend film has risen from 15.26 % to 15.91 %. After 312 hours of stability testing, the aforementioned doped devices still have device performance higher than standard device. Furthermore, based on PBDB-T: IT-M mix film, the PCE of the doped device and reference device was 11.29 % and 10.55 %, respectively. This study suggests that using the alcohol-soluble small-molecule material Glycolic acid can increase the organic solar cells' (OSCs') efficiency. This study provides a new method for manufacturing high-performance OSCs.

Application of isoindigo-based small molecule conjugated electrolytes at interfaces with organic solar cells

Zwitterionic small molecule materials are widely employed in the cathode interface layer of organic solar cells (OSCs). Nevertheless, the exploration of superior cathode interface materials with the objective of enhancing the performance of OSCs remains a significant challenge. Two water/alcohol soluble n-type self-doped small molecule conjugated electrolytes were synthesized using isoindigo as the acceptor unit and triphenylamine (TPA) as the donor unit. Quaternary ammonium salts or pyridine salts were used as the polar side chains. When applied to organic solar cells (OSCs) with PTB7-Th: PC71BM as the active layer, the devices showed improved performance. The power conversion efficiency (PCE) reached 8.59 % (IIDN2TPA) and 8.81 % (IIDPy2TPA), respectively. These results demonstrate the water/alcohol-soluble D-A-D-type small-molecule conjugated electrolytes offer an effective strategy in designing cathode interlayer (CIL) and preparing the high-performance OSCs.

Novel self-doping alcohol-soluble quinacridone-based small molecule at the cathode interface layer of organic solar cells

Interfacial modification plays a crucial part in improving the photovoltaic performance and stability of organic solar cells (OSCs). The self-doping effect can enhance the inter-ohmic contact at the active layer material with the cathode. Therefore, we synthesised a self-doping alcohol-soluble quinacridone-based small molecule, 5,12-bis(3-(dimethylamino)propyl)-5,12-dihydroquinolo[2,3-b]acridine-7,14-dione (QAN), with a self-doping effect, and introduced QAN as cathode interfacial layers (CILs) into OSCs. The central nuclear structure of QAN is an electron-deficient unit with a large conjugated structure. This structure facilitates electron transport as a cathode-interface material. Additionally, its polar side chains enhance the solution-processing capability and contribute to a more pronounced self-doping effect. Compared with the devices without interfacial material, the open-circuit voltage(VOC) and short-circuit current (JSC) with QAN as an interfacial material increased. What's more, the optimal photoelectric conversion efficiency (PCE) of the QAN CIL device is increased to 9.05 % for the same experimental conditions, which is 40 % higher than the device without interface material. By characterizing the surface morphology, it was found that the PTB7-Th:PC71BM active layer devices exhibited a smooth surface morphology and improved hydrophilicity when inserted with QAN CIL, which helps to enhance the physical contact of the active layer with the cathode, in addition to charge extraction and transport. This result suggests that introducing QAN as the CILs of the device is a viable way to improve the performance of the OSCs.

High Open-Circuit Voltage Wide-Bandgap Perovskite Solar Cell with Interface Dipole Layer.

Wide-bandgap perovskite solar cells (PSCs) with high open-circuit voltage (Voc) represent a compelling and emerging technological advancement in high-performing perovskite-based tandem solar cells. Interfacial engineering is an effective strategy to enhance Voc in PSCs by tailoring the energy level alignments between the constituent layers. Herein, n-type quinoxaline-phosphine oxide-based small molecules with strong dipole moments is designed and introduce them as effective cathode interfacial layers. Their strong dipole effect leads to appropriate energy level alignment by tuning the work function of the Ag electrode to form an ohmic contact and enhance the built-in potential within the device, thereby improving charge-carrier transport and mitigating charge recombination. The organic interfacial layer-modified wide-bandgap PSCs exhibit a high Voc of 1.31V (deficit of <0.44V) and a power conversion efficiency (PCE) of 20.3%, significantly improved from the device without an interface dipole layer (Voc of 1.26V and PCE of 16.7%). Furthermore, the hydrophobic characteristics of the small molecules contribute to improved device stability, retaining 95% of the initial PCE after 500h in ambient air.

Direct arylation-derived non-ionic star-shaped oligomeric CIL materials with Dramatically reduced work functions for organic solar cells

Although numerous photoactive layer materials have been explored for organic solar cells (OSCs), the cathode interface layer (CIL) materials still largely lag behind, however. Till now, ionic perylene diimide (PDI) derivatives are one of the most representative conjugated small molecules CIL materials for OSC. In this study, three new non-ionic star-shaped oligomeric CIL materials named W1, W2 and W3 involving 1,3,5-tribromo-2,4,6-trifluoro-benzene building, cyclopentadithiophene, rhodamine and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile blocks were designed and facilely synthesized via atom-economic direct C–H arylation for OSC. In the follow-up study of structure-property correlation, it was found that all three molecules possess the deepened work function (WF). W1-3 show good electron transport, and are introduced into the PM6:Y6 system to further explore its effect as CIL that, can effectively suppress charge recombination. Among them, W1 has the best effect of reducing the WF, which reduces the WF of the Ag electrode from 4.30 eV to 3.41 eV. Owing to its deepest WF and best alcoholic processability. The W1-based devices achieve a highest-power conversion efficiency (PCE) of 14.53 %, corresponding to a VOC of 0.85 V, a JSC of 25.17 mA cm−2, and an FF of 67.21 %. Our work opens up a new direction for non-ionic, non-PDI and non-fused ring star-shaped CIL materials, and thus diversify the CIL materials.

Electron Transporting Polymeric Materials with Partial Quaternization for High-Performance Organic Solar Cells.

Efficient cathode interfacial layers (CILs) have become a crucial component of organic solar cells (OSCs). Charge extraction barriers, interfacial trap states, and significant transport resistance may be induced due to the unfavorable cathode interlayer, limiting the device performance. In this study, poly(4-vinylpyridine) is used as the CIL for OSCs, and a new type of CIL named P4VP-I is synthesized through the quaternization strategy. Compared to P4VP, P4VP-I CIL exhibits enhanced conductivity and optimized work function. OSCs employing the P4VP-I ETL demonstrate prolonged carrier lifetime, suppressed charge recombination, and achieve higher power conversion efficiencies (PCE) than the commonly used ETLs such as PFN-Br and Phen-NaDPO.

Improving the operating performance of organic solar cells through a novel cathode interface layer

In the classical system of organic PSCs (PTB7-Th: PC71BM), the presence of a cathode interface layer has the function of improving the device performance by lowering the interfacial barrier between the active layer and the electrode, increasing the charge selectivity, regulating the morphology of the active layer, and regulating the absorption of sunlight by the active layer. Therefore, a novel alcohol-soluble electron transport material is synthesized in this paper, which can cause a more prominent self-doping effect by enhancing intramolecular conjugation, and the results show that in terms of exciton dissociation and recombination, it is found that bimolecular recombination and trap-assisted recombination are obviously inhibited, so that the battery using this interface obtains more than 69% of the fill factor (FF) and has a superior energy conversion efficiency (PCE).

Small molecule perylene diimide derivatives with different bay site modifications as cathode interface layers for organic solar cells

Cathode interface layers (CILs) can effectively elevate the performance of organic solar cells (OSCs), and the development of CILs with high thickness insensitivity is the focus of commercializing OSCs. Perylene diimide (PDI) derivatives proved to be potential CILs, and bay modification could further adjust the coplanarity and optimize the film-forming properties of PDI-based CILs. Thus, two novel CILs with intermediate-sized spacer groups were synthesized (PDINN-P3P and PDINN-TPA). In contrast to PDINN-P3P with m-diphenylbenzene, PDINN-TPA with triphenylamine can form stronger self-doping between the side chain of triphenylamine and the PDI backbone, resulting in higher charge transport capacity and better interface regulation ability. PDINN-TPA-based OSCs demonstrated a higher power conversion efficiency (PCE) of 16.11 % in the PM6:Y6 system, outperforming the PCE of PDINN-P3P-based OSCs (15.00 %). Meanwhile, PDINN-TPA expressed a favorable thickness processing range, a PCE of 14.19 % can be maintained with a thickness up to 35 nm. After storing in the glove box for 114 h, PDINN-TPA-based OSCs can exhibit excellent long-term stability (over 90 % of the optimal PCE). Besides, PDINN-P3P and PDINN-TPA were further utilized CILs in the PM6: BTP-eC9 system, and the PDINN-TPA-based OSCs acquired a PCE of 16.91 % (15.54 % for PDINN-P3P-based OSCs), highlighting the broad applicability of PDINN-P3P and PDINN-TPA. This study confirms that the synergistic effect of bay site modification and n-type self-doping on PDI can simultaneously optimize the thickness insensitivity and long-term stability of PDI-based CILs.

Synergistically Modulating the Bay and Amid Sites of a Perylene Diimide Cathode Interface Layer for High-Efficiency and High-Stability Organic Solar Cells

Synergistically Modulating the <i>Bay and Amid</i> Sites of a Perylene Diimide Cathode Interface Layer for High-Efficiency and High-Stability Organic Solar Cells

Optimizing of Cathode Interface Layers in Organic Solar Cells Using Polyphenols: An Effective Approach

Optimizing of Cathode Interface Layers in Organic Solar Cells Using Polyphenols: An Effective Approach

N-type small molecule electrolyte cathode interface layer with thickness insensitivity for organic solar cells

Interface engineering has a critical impact on the performances of organic solar cells (OSCs). And cathode interface layer (CIL) with thickness insensitivity is urgently pursued to improve the possibility of industrialization of OSCs. N-type self-doping has been proven effective in increasing electron mobility. Here, four novel n-type small molecule electrolytes (SMEs) with diverse counter anions (CAs), PDIN-BF4, PDIN-BPh4, PDIN-BPhF4, and PDIN-BIm4 were synthesized and employed as cathode interface layers (CILs). Among them, PDIN-BIm4-based OSCs with PM6:Y6 active layer achieved the most glorious electron mobility and thickness insensitivity with a power conversion efficiency (PCE) of 16.98 % due to outstanding self-doping effect and interfacial regulation ability. However, the multi-F atoms on PDIN-BPhF4 may prevent self-doping progress and impede electron transport, thus leading to a low PCE of 11.53 %. Meanwhile, the PDIN-BIm4-based device can maintain over 80 % of the optimal PCE with a thickness of 43 nm or storing in a glove box for 600 h. In addition, PM6: BTP-eC9-based device with PDIN-BIm4 CIL acquired a PCE of 17.82 %, highlighting the broad applicability of PDIN-BIm4. Our work demonstrates that the introduction of CAs into n-type organic materials helps promote the progress of efficient and stable OSCs.

Self‐doped conjugated polymers with electron‐deficient quinone units for enhanced electron transport in highly efficient organic solar cells

AbstractOrganic solar cells (OSCs) have attracted significant attention as a burgeoning flexible technology, owing to their advanced power conversion efficiencies. Moreover, interface materials play a crucial role in optimizing energy level alignment between the active layer and electrodes, thereby enhancing carrier extraction within the device and improving efficiency. However, current methodologies for fabricating electron‐transport materials with superior mobility are still limited compared with those for hole‐transport materials. In this study, a benzodifurandione (BFDO)‐derived building block with quinone resonance property and strong electron‐withdrawing capability was synthesized. Two conjugated polymers, namely PBFDO‐F6N and PBFDO‐F6N‐Br, were prepared, both of which exhibited good electron mobility and exceptional interface modification capabilities. A comprehensive investigation of the interaction between the interface layer and the active layer revealed that PBFDO‐F6N induced doping at the acceptor interface. Additionally, the high mobility of PBFDO‐F6N facilitated efficient carrier extraction at the interface. Consequently, the application of PBFDO‐F6N as the cathode interface layer for PM6:BTP‐eC9‐based OSC devices resulted in a remarkable efficiency of 18.11%. Moreover, the device efficiency remained at ∼96% even at a PBFDO‐F6N interface thickness of 50 nm, demonstrating the great potential of this material for large‐scale device preparation.

Cathode interface layer based on organosilica nanodots for stabilized inverted organic solar cells

Cathode interface layer based on organosilica nanodots for stabilized inverted organic solar cells

In Situ-Initiated Poly-1,3-dioxolane Gel Electrolyte for High-Voltage Lithium Metal Batteries.

To realize high-energy-density Li metal batteries at low temperatures, a new electrolyte is needed to solve the high-voltage compatibility and fast lithium-ion de-solvation process. A gel polymer electrolyte with a small-molecular-weight polymer is widely investigated by combining the merits of a solid polymer electrolyte (SPE) and liquid electrolyte (LE). Herein, we present a new gel polymer electrolyte (P-DOL) by the lithium difluoro(oxalate)borate (LiDFOB)-initiated polymerization process using 1,3-dioxolane (DOL) as a monomer solvent. The P-DOL presents excellent ionic conductivity (1.12 × 10-4 S cm-1) at -20 °C, with an oxidation potential of 4.8 V. The Li‖LiCoO2 cell stably cycled at 4.3 V under room temperature, with a discharge capacity of 130 mAh g-1 at 0.5 C and a capacity retention rate of 86.4% after 50 cycles. Moreover, a high-Ni-content LiNi0.8Co0.1Mn0.1O2 (NCM811) cell can steadily run for 120 cycles at -20 °C, with a capacity retention of 88.4%. The underlying mechanism of high-voltage compatibility originates from the dense and robust B- and F-rich cathode interface layer (CEI) formed at the cathode interface. Our report will shed light on the real application of Li metal batteries under all-climate conditions in the future.

Bias‐Switchable Dual‐Mode Organic Photodiodes Enabled by Manipulation of Interface Layers

AbstractBias‐switchable dual‐mode organic photodiodes (OPDs) that integrate photovoltaic and photomultiplication modes are recently developed and shown prospects in complex light‐intensity applications. Yet, the device physics that focuses on carrier dynamics is still a challenge and needs to be further explored. Herein, dual‐mode OPDs are developed through interface layer manipulation, that is, introducing cathode interface layers (typically, ZnxO:D149) with deep energy levels and abundant bulk defects and an anode interface layer of thermally‐evaporated ZnO (e‐ZnO) with a wide bandgap. Under reverse bias, ZnxO:D149 forms a barrier wall to effectively block external holes and maintain the photovoltaic mode of the OPDs. Under forward bias, the capturing effect of ZnxO:D149 and blocking effect of e‐ZnO help to reduce the dark current; when under illumination, defect traps capture photo‐generated holes, eliminating the barrier traps and promoting unobstructed injection of external carriers to achieve photomultiplication effect. The typical device delivers high specific detectivity (&gt;1012 Jones) and fast response (&lt;40 µs), and exhibits disparate external quantum efficiency in two operating modes, showing promise for simultaneously detecting faint and strong light. This general strategy for preparing dual‐mode OPDs is compatible with CMOS processing technology and meets the miniaturization and integration requirements of next‐generation detection systems.

Improving the performance and stability of inverted perovskite solar cell modules by cathode interface engineering

Perovskite solar cells (PSCs) represent a highly promising photovoltaic technology wherein a low-work function metal cathode is essential for efficient electron collection. The effectiveness of PSCs is significantly enhanced by a well-designed cathode interface layer (CIL). Characterized by their simple structure and impressive modification capabilities, small-molecule CILs hold considerable commercial potential for advancing the performance of PSCs. Herein, we synthesized a conjugated small-molecule CIL, named FY1, for modulating the cathode interface of inverted PSCs to enhance the power conversion efficiency (PCE) and long-term stability. FY1 not only optimized the molecule/metal contact to reduce traps but also uniformly improved the efficiency and speed of extracting photogenerated electrons, facilitating their effective extraction at the cathode interface. FY1 modification reduced the work function of Ag, subsequently lowering the energy barrier for electron transfer from the electron transport layer to the external cathode metal. By employing FY1 as a CIL, a record-high PCE of 23.72 % and a fill factor of 82.3 % were achieved in inverted PSCs. Furthermore, FY1 modification increased the PCE of PSC modules with an active area of 14 cm2 to 21.8 %; after continuous illumination for 850 h, it retained approximately 98.5 % of the initial efficiency. These findings show that FY1 can assist in unlocking the full potential of this emerging photovoltaic technology.

Improved efficiency of polymer solar cells using alcohol-soluble self-doped N-type polymers as cathode interface layer

Extensive research has been conducted on polymeric cathode interface substances, known for their self-doping features, for their application in organic solar cells (OSCs) to improve the ohmic interaction at the electrode with the active layer. In this paper, two novel polymers, PIIDN-F and PIIDN-FN, with self-doping effect, were successfully synthesized by combining isoindigo (IID), which contains an amino side chain, as an electrons-deficient group with fluorene, which contains different side chains. A thorough examination was conducted on the self-doping properties, electrical conductivity, work efficiency, and the angle of water contact between the two substances. Following this, PIIDN-F and PIIDN-FN were effectively utilized as cathode interface layers (CILs) within PTB7-Th:PC71BM OSCs. The PIIDN-F and PIIDN-FN achieve power conversion efficiencies (PCEs) of 8.97% and 9.04%, respectively. Findings indicate that the quantity of polar groups significantly influences the polymer's conductivity, adjustable work function, and the interaction at interfaces. These results show that by simply adjusting the number of polar groups, it is possible to provide efficient CILs for high-performance OSCs.

High Performance Organic Solar Cells Prepared with Bi‐Triangular Pyramidal Organic Phosphonium Interface Material

AbstractNowadays, amine containing electrode interface material destroy the non‐fullerene acceptor becomes a hard nut to crack for organic solar cells. Developing water‐soluble interface material which is no chemical reaction with non‐fullerene acceptor is an important research theme. Here, we report two bi‐triangular pyramidal electronic configuration organic‐phosphonium bromides as non‐amine cathode interfacial layer for fabricating high‐efficiency stable organic solar cells. The power conversion efficiency (PCE) of inverted device structure with PBDB‐T/ITIC as active layer is up to 11.58 % which is great larger than control device PCE (9.35 %). Same device structure with PM6/Y6 as active layer, the PCE is up to 15.26 % and also is dramatically higher than the referred device PCE 14.36 %. Meanwhile, the devices show greatly improved stability by organic‐phosphonium bromide interlayer.

Enhanced efficiency of organic solar cells through trans-cinnamic acid doped cathode interface layer

Enhanced efficiency of organic solar cells through trans-cinnamic acid doped cathode interface layer