Cathode Interfacial Materials Research Articles

Advances in anode interfacial materials for organic solar cells

AbstractOrganic solar cells (OSCs) have attracted much interest in the past few decades because of their advantages, such as being lightweight, low cost, simple preparation process, and environmental friendliness. While researchers have made significant progress on the active layer materials of OSCs, the interface engineering is another entry point for upgrading the photovoltaic performance of OSCs. Significantly, the interface modification materials, including anode interfacial materials and cathode interfacial materials, are two essential parts of interfacial layers for OSCs, in which the excellent interfacial materials can realize the very high‐performance photovoltaic cells. Among these interfacial materials, the anode interfacial layers (AILs) play a crucial role in improving photovoltaic performance. This review expresses a detailed conclusion of the development of anode interfacial materials and an outlook on future trends for OSCs.

Propeller-shaped NI isomers of cathode interfacial material for efficient organic solar cells

Propeller-shaped NI isomers of cathode interfacial material for efficient organic solar cells

Amino-Functionalized Graphdiyne Derivative as a Cathode Interface Layer with High Thickness Tolerance for Highly Efficient Organic Solar Cells.

Efficient cathode interfacial materials (CIMs) are essential components for effectively enhancing the performance of organic solar cells (OSCs). Although high-performance CIMs are desired to meet the requirements of various OSCs, potential candidates for CIMs are scarce. Herein, an amino-functionalized graphdiyne derivative (GDY-N) is developed, which represents the first example of GDY that exhibits favorable solubility in alcohol. Utilizing GDY-N as the CIM, an outstanding champion PCE of 19.30% for devices based on the D18-Cl:L8-BO (certified result: 19.05%) is achieved, which is among the highest efficiencies reported to date in OSCs. Remarkably, the devices based on GDY-N exhibit a thickness-insensitive characteristic, maintaining 95% of their initial efficiency even with a film thickness of 25nm. Moreover, the GDY-N displays wide universality and facilitates exceptional stability in OSCs. This work not only enriches the diversity of GDYderivatives, but also demonstrates the feasibility of GDY derivatives as CIMs with high thickness tolerance in OSCs.

Halogen substitution of perinone-based cathode interfacial materials for high-efficiency inverted perovskite solar cells

A fluorine-substituted perinone derivative exhibits better cathode interfacial modification than the chlorine-substituted one in inverted perovskite solar cells.

Phenanthroline-carbolong interface suppress chemical interactions with active layer enabling long-time stable organic solar cells

To restrain the chemical reaction at cathode interface of organic solar cells, two cathode interfacial materials are synthesized by connecting phenanthroline with carbolong unit. Consequently, the D18:L8-BO based organic solar cell with double-phenanthroline-carbolong achieve the highest efficiency of 18.2%. Double-phenanthroline-carbolong with larger steric hindrance and stronger electron-withdrawing property confirms to suppress the interfacial reaction with norfullerene acceptor, resulting the most stable device. Double-phenanthroline-carbolong based device can sustain 80% of its initial efficiency for 2170 h in dark N2 atmosphere, 96 h under 85 oC and keep 68% initial efficiency after been illuminated for 2200 h, which are significantly better than bathocuproin based devices. Moreover, superb interfacial stability of double-phenanthroline-carbolong cathode interface enables thermal posttreatment of organic sub-cell in perovskite/organic tandem solar cells and obtained a remarkable efficiency of 21.7% with excellent thermal stability, which indicates the potentially wide application of phenanthroline-carbolong materials for stable and efficient solar device fabrications.

Bay-Functionalized Perylene Diimide Derivative Cathode Interfacial Layer for High-Performance Organic Solar Cells.

The field of organic solar cells (OSCs) has acquired rapid progress with the development of nonfullerene acceptors. Interfacial engineering is also significant for the enhancement of the power conversion efficiency (PCE) in OSCs. Among the cathode interfacial materials (CIMs), perylene diimide (PDI) small molecules are promising owing to the excellent electron affinity and electron mobility. Although the well-known PDINN molecule has excellent properties, it has a high planarity formed by an extensive rigid π-conjugated backbone. Because the PDI molecular backbone has a strong tendency to aggregate, it causes the problem of excessive molecular aggregation and stacking, which directly leads to excessive crystallinity. Proper accumulation is beneficial for charge transport, but oversized crystals formed by overaggregation will hinder charge transport, ultimately affecting the film morphology and charge transport efficiency. Modifying the bay position of PDINN is an effective strategy to reduce the planarity, modulate the molecular aggregation, optimize the morphology, and enhance the charge-collecting efficiency. Therefore, PDINN-S was synthesized from PDINN by substituting the hydrogen with thiophene. The optimal PCE in the PM6:Y6 active layer was 16.18% and remained at 80% of the initial value after 720 h in a glovebox. This provides some guidance for exploring CIMs and preparing large-scale OSCs in the future.

Natural Materials for Sustainable Organic Solar Cells: Status and Challenge

AbstractThe exploitation of natural materials has received growing attention because of the needs of environmental sustainability. In contrast to petroleum‐based synthetic materials, natural materials possess significant advantages of abundant, low‐cost, degradable, and renewable. Here, the recent research status of natural materials as flexible substrate, cathode interfacial material, and anode interfacial material for organic photovoltaics (OPVs) are first presented. Then, the confronted key challenges that limit the widespread application of natural materials for OPVs is summarized, including complex multilength scaled aggregation morphology, non‐conjugated structure, and unclear working mechanism. Finally, their potential solutions from the perspective of chemical structure are proposed for constructing efficient OPVs. It is believed that natural materials have a broad landscape in low‐cost and green manufacturing technology for OPVs in the future.

Phosphotungstate-Based Anode Interfacial Material for Constructing High-Performance Polymer Solar Cells with a Fill Factor over 80.

In the field of organic solar cells (OSCs), the interfacial layer plays the role of enhancing carrier extraction/transportation, inhibiting their recombination, etc. In contrast to the wide variety of cathode interfacial materials with good modification ability, much less effort has been reported for anode interfacial materials. In this study, we report a polyoxometalate-based inorganic molecular cluster, zinc phosphotungstate (Zn3P2W24O80, denoted ZnPW), as an anode interfacial layer. Based on the PM6/EH-HD-4F/L8-BO-F ternary system, the device with ZnPW modification achieved a high power conversion efficiency (PCE) and a fill factor of up to 18.67 and 80.29%, respectively, which are higher than the counterpart device (PCE of 18.01%) with PEDOT/PSS as the anode interfacial layer. Detailed studies revealed that under the modification of ZnPW, the devices obtained promoted light absorption and suitable energy level matching between the active layer and the electrode, reduced contact resistance, and suppressed charge recombination. In addition, the ZnPW-modified devices had improved photostability and storage stability compared to PEDOT/PSS-modified devices. Our work shows that the polyoxometalate-based inorganic nanocluster ZnPW has great advantages in enhancing the device performance and stability of OSCs.

Polar side-chain tuning of perylene diimide and fluorene-based cathode interfacial material for high-performance inverted perovskite solar cells

Cathode interface layers (CILs) play an important role in inverted perovskite solar cells (PVSCs) to correct the mismatched energy levels, improve electron extraction, and passivate interfacial defects.

A Simple Cathode Interfacial Material Performs Well in Organic Solar Cells

A low‐cost perylene‐diimide diphosphonium bromide cathode interlayer material ((1,3,8,10‐tetraoxo‐1,3,8,10‐tetrahydroanthra[2,1,9‐def:6,5,10‐d'e’f']diisoquinoline‐2, 9‐diyl)bis(4,1‐phenylene))bis(triphenylphosphonium)bromide (named as CIL‐4), whose photovoltaic performance is comparable with recognized poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethylammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluor ene)] (PFN‐Br) is reported in this article. Unlike PFN‐Br, CIL‐4 is easy to prepare and well soluble in highly polarized solvents such as H2O, CH3OH, and DMF. An impressive power conversion efficiency (PCE) of 15.08% is demonstrated. In addition, CIL‐4 is very cost‐effective because of the one‐step synthesis and purification method. CIL‐4 also favorably tends to form a high‐quality amorphous films by a simple solution process. The femtosecond transient absorption (TA) experiment verified electron transfer occurs between n‐type electron acceptor Y6 and the CIL‐4 film interface. This work indicates that perylene‐diimide diphosphonium bromide can be a competent cathode‐adjusting material in the optoelectronic field.

One-step synthesis of low-cost perylenediimide-based cathode interfacial materials for efficient inverted perovskite solar cells

Interface engineering plays an important role in improving the performance of perovskite devices. Herein, we reported two perylenediimide small molecular cathode interface materials (CIMs), PDI-2N and PDI-4N, synthesized by a simple method and with good alcohol soluble, which could be used as cathode interfacial layer (CIL) for high-performance inverted perovskite solar cells (PVSCs). The PDI-4N exhibits larger electrical conductivity, electron mobility and self-doping properties than PDI-2N because of more dimethylamino functional groups in the amide positions. Based on these superiorities, a peak PCE of 21.33% with PDI-4N as CIL was achieved, which is the highest PCE for PDI-based interlayer materials as the cathode interlayer in inverted PVSCs. While the PCE with PDI-2N as CIL is only 17.41%. The significant improvement in device efficiency for PDI-4N based device is due to reduced defect density, lower dark current, larger recombination resistance and better surface morphology, which improved charge transport and collection at the PC61BM/Ag interface. Moreover, the ambient stabilities of PVSCs with PDI-2N and PDI-4N as CIL show that the CILs can effectively improve the device stability, and good stability with a PCE loss of only ∼3.0% after 600 h is also obtained. In a word, this work will provide us with molecular design approach by one-step to develop novel cathode interface materials with functional side chains for high-efficiency PVSCs.

“A-π-A” type naphthalimide-based cathode interlayers for efficient organic solar cells

In this work, we designed and synthesized two “A-π-A” structural small molecules based on N-dimethylaminopropyl-1,8-naphthalimide with π-bridge, namely 4,4'-(thiophene-2,5-diyl)bis(2-(3-(dimethylamino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione) (ONTN) and 4,4'-(1,4-phenylene)bis(2-(3-(dimethylamino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione) (ONBN), which are used as cathode interfacial materials (CIMs) to systematically reveal the effect of π-bridge of 1,8-naphthalimide-based cathode interlayers for efficient organic solar cells (OSCs). Compared with ONBN, ONTN shows higher decomposition temperature, more red-shift absorption, lower LUMO and higher HOMO energy levels, higher electron mobility and conductivity, and more uniform film morphology. Both molecules exhibit excellent thermal stability and high light transmittance. The OSCs based on ONTN with PBDB-T:ITIC as active layer demonstrate a power conversion efficiency (PCE) of 10.38%, higher than the control device of ONBN (a PCE of 9.04%). It turns out that thiophene π-bridge 1,8-naphthalimide-based ONTN got better performance as CIMs than that of ONBN with benzene π-bridge.

A Cathode Interface Layer Based on 4,5,9,10-Pyrene Diimide for Highly Efficient Binary Organic Solar Cells.

Efficient cathode interfacial layers (CILs) are becoming essential elements for organic solar cells (OSCs). However, the absorption of commonly used cathode interfacial materials (CIMs) is either too weak or overlaps too much with that of photoactive materials, hindering their contribution to the light absorption. In this work, we demonstrate the construction of highly efficient CIMs based on 2,7-di-tert-butyl-4,5,9,10-pyrene diimide (t-PyDI) framework. By introducing amino, amino N-oxide and quaternary ammonium bromide as functional groups, three novel self-doped CIMs named t-PyDIN, t-PyDINO and t-PyDINBr are synthesized. These CIMs are capable of boosting the device performances by broadening the absorption, forming ohmic contact at the interface of active layer and electrode, as well as facilitating electron collection. Notably, the device based on t-PyDIN achieved a power conversion efficiency of 18.25 %, which is among the top efficiencies reported to date in binary OSCs.

A Cathode Interface Layer Based on 4,5,9,10‐Pyrene Diimide for Highly Efficient Binary Organic Solar Cells

AbstractEfficient cathode interfacial layers (CILs) are becoming essential elements for organic solar cells (OSCs). However, the absorption of commonly used cathode interfacial materials (CIMs) is either too weak or overlaps too much with that of photoactive materials, hindering their contribution to the light absorption. In this work, we demonstrate the construction of highly efficient CIMs based on 2,7‐di‐tert‐butyl‐4,5,9,10‐pyrene diimide (t‐PyDI) framework. By introducing amino, amino N‐oxide and quaternary ammonium bromide as functional groups, three novel self‐doped CIMs named t‐PyDIN, t‐PyDINO and t‐PyDINBr are synthesized. These CIMs are capable of boosting the device performances by broadening the absorption, forming ohmic contact at the interface of active layer and electrode, as well as facilitating electron collection. Notably, the device based on t‐PyDIN achieved a power conversion efficiency of 18.25 %, which is among the top efficiencies reported to date in binary OSCs.

Achieving the low interfacial tension by balancing crystallization and film-forming ability of the cathode interlayer for organic solar cells

A series of molecules with imide units bridged by the core of thiophene-based groups, namely N-dimethylaminopropyl-4-thiophene-1,8- naphthalimide (NT), bis(N-dimethylaminopropyl)-4-thiophene-1,8-naphthalimide (NTN), and bis(N-dimethylaminopropyl)-4-bithiophene-1,8-naphthalimide (N2TN), have been reported as cathode interfacial materials (CIMs) to realize low interfacial tension with the blend in organic solar cells (OSCs). We evaluated the Ohmic contact between the active layer and these cathode interlayers basedon various characterizations, which is of great significance for further understanding these imide-based interlayers. It turned out that the homogeneous and continuous NTN interlayer as a CIM balanced the factors of crystallization and film-forming property, and broke through the limitation of poor conductivity and high aggregation in our previous work. Moreover, compared with NT and N2TN, the NTN interlayer achieve a combination of good solubility in methanol, efficient electron mobility, and aligned work function. These advantages of NTN are conducive to the realization of high-efficient interfacial electron collection and transfer, thus improving the short-circuit current density (JSC) and filling factor (FF) of devices. Therefore, the binary OSCs (PM6:Y6) based on NTN engineered aluminium-cathode with excellent stability demonstrate a maximum power conversion efficiency (PCE) of 16.56 %, which is higher than NT (PCE = 1.34 %) and N2TN (PCE = 13.90 %). The enhanced performance is ascribed to the improvement of JSC and FF, which is originated from the outstanding conductivity and high-quality interface of NTN. Surprisingly, the PM6:Y6-based semitransparent device with NTN obtain a PCE of 13.43 % with an average visible transmittance of 17.79 %, which is better than traditional PDINO. This study highlights a potential strategy for enhancing the performance of OSCs by the interface engineering via decreasing the interfacial intension.

Glucose and Its Derivatives as Interfacial Materials for Inverted Organic Solar Cells.

Glucose, a widely distributed biomaterial in nature, is presented as a new cathode interfacial material for highly efficient inverted organic solar cells. The interactions between glucose and the indium tin oxide (ITO) substrate as well as the formation mechanisms of the glucose interlayer were investigated by molecular dynamics simulation and relevant experimental tests. The results revealed that the In-OH coordination between the oxygen atom of glucose and the indium of ITO is the key factor for the formation of interfacial dipoles, thereby reducing the work function of the ITO cathode for efficient charge transfer. With PM6:Y6 as the active layer, the power conversion efficiency (PCE) of the organic solar cells was significantly increased from 1.99 to 15.42% after ITO was modified by a glucose interlayer through the traditional spin-coating method. More importantly, glucose can be adsorbed on the ITO surface by a simple immersion process, and the devices based on the modified ITO by immersed glucose achieved a PCE of 14.48%, which is comparable to that of the traditional spin-coating method. Furthermore, we found that the OSCs with the ITO cathodes modified with glucose derivatives including sorbitol and sodium gluconate by different preparation methods also exhibited high performance. The overall performance of the devices with ITO modified by a simple and low-cost immersion method can be maintained at more than 93% of that prepared with the traditional spin-coating method. The results demonstrated that low-price glucose and its derivatives are good candidates as ITO interlayer materials for OSCs, and the effectiveness of the immersion process paves a way for simplifying the manufacture of low-cost and large-area organic solar cells.

Aminonaphthalimide-Based Molecular Cathode Interlayers for As-Cast Organic Solar Cells.

A series of imide-based small molecules, namely NA, NAA, and NEA with simple structures, were designed and synthesized by introducing different amine side-chains into the benzene unit of imide, which were used as cathode interfacial materials in organic solar cells (OSCs). The amine side-chain substitution positions were systematically investigated with these small-molecule imides. Compared with NA without amide chains-NAA, and NEA, with 3-dimethylaminopropylamine and ethylenediamine chains, respectively-show bathochromic shifts in absorption, decreased band gaps, and higher highest occupied molecular orbital (HOMO) energy levels. A power conversion efficiency (PCE) of 15.04 % was obtained with the NEA-based as-cast OSCs with a high open-circuit voltage and fill factor for PM6 : Y6 blend and the maximum PCE of 15.80 % was reached for as-cast PM6 : Y6 : IT-M ternary OSCs. NEA exhibits better conductivity, higher electron mobility, and stronger the capability of lower work function of cathode among three molecules, affording OSCs with better photovoltaic performance. Additionally, these three molecules show excellent thermal stability both in solution and in films at 150 °C. The results indicate that imide-based small molecules are promising cathode interfacial materials for commercial OSCs.

8‐Hydroxyquinoline Metal Complexes as Cathode Interfacial Materials in Inverted Planar Perovskite Solar Cells

AbstractIon migration is a crucial factor influencing the stability of perovskite solar cells. Insertion of an interfacial layer between the electron‐transporting layer and the cathode is shown to be an effective way to enhance the performance of devices. However, exploring more effective interfacial materials to block ion migration and thus enhance the device stability is still needed. Herein, a series of 8‐hydroxyquinoline metal complexes are employed as cathode interfacial layers (CILs) in inverted planar perovskite solar cells. The devices with CILs exhibit better performance, stability, and reproducibility than the control device without CILs. The introduction of the CILs forms a better energy match between the [6,6]‐phenyl‐C61‐butyric acid methyl ester layer and the cathode, reduces the contact resistance, accelerates the charge transfer, and suppresses non‐radiative recombination. Moreover, the CILs protect the device from moisture and block the ion diffusions, which is beneficial for device stability. After optimization, the best power conversion efficiency of 20.6% is obtained by using 8‐hydroxyquinoline aluminum (Alq3) as a CIL, and the efficiency remains 85% of its initial value after 800 h continuous illumination.

Single-wall carbon nanotube-containing cathode interfacial materials for high performance organic solar cells

Single-wall carbon nanotube-containing cathode interfacial materials for high performance organic solar cells

An alcohol-soluble small molecule as efficient cathode interfacial layer materials for polymer solar cells

Abstract Interface modification makes an important contribution to improving the optoelectronic performance and stability of polymer solar cells (PSCs). Here, the hexamethylenetetramine (C6H12N4) was successfully introduced into PSCs as cathode interface layers (CILs) using environmental-friendly methanol as solvent. Compared to the PSCs without CILs, the open circuit voltage (VOC) and short-circuit current density (JSC) of the device with C6H12N4 CILs was increased from 0.44 V to 12.73 mA cm−2 to 0.77 V and 15.89 mA cm−2, respectively. More importantly, under the same experimental conditions, the optimal power conversion efficiency (PCE) of the device with C6H12N4 CILs was improved to 7.79%, which is 185% higher than that of the device without C6H12N4 CILs (2.73%). We found that the active layer PTB7-Th:PC71BM showed a smoother interface morphology and better hydrophilicity after insertion of CILs, which facilitated enhance the physical contact between active layers and cathode as well as electron extraction and transport. The results show that the introduction of C6H12N4 as CILs provides an effective method for preparing high-performance PSCs.