Inverted Organic Photovoltaics Research Articles

Aqueous PEIE Soaking on ZnO for Ultraviolet Light Activation-Free Organic Photovoltaic Modules.

Ultraviolet (UV) light is typically needed to activate inverted organic photovoltaics (OPVs) with zinc oxide (ZnO) as electron transporting layer (ETL)for higher efficiency. However, UV light is a major cause for the degradation of organic active layers in OPVs. This is a contradiction that UV light activation enhances the efficiency but UV illumination deteriorates the stability. It is important to solve this contradiction to develop UV light activation-free OPV devices. Herein, a method of aqueous polyethylenimine ethoxylated (PEIE) soaking on ZnO is reported to realize UV light activation-free OPV devices. The S-shape in current density-voltage (J-V) characteristics of devices tested without UV light activation is eliminated through the treatment of aqueous PEIE soaking on ZnO. The treatment reduces the oxygen adsorbates, which is confirmed by Kelvin probe and X-ray photoelectron spectroscopy. A 10.08 cm2 organic photovoltaic module with the treated ZnO asETL showed high photovoltaic performance: VOC = 5.68 V, JSC = 2.7 mAcm-2, FF = 75.1%, and POutput = 11.5 mWcm-2 tested with the UV filter (light intensity of 0.788 sun). UV light activation is not needed for the modules to obtain high efficiency.

An Overview of Electron Transport Layer Materials and Structures for Efficient Organic Photovoltaic Cells

The electron transport layer (ETL) has gained significant attention recently for its essential role in facilitating charge extraction, transportation, and reducing recombination in photovoltaic cells. Organic photovoltaics (OPVs) with ETLs have achieved remarkable efficiencies exceeding 19%, and indoor OPVs have reached a peak efficiency of 29.4% under 3000 LX illumination. Despite these accomplishments, the difficulties in choosing appropriate ETLs for contact alignment have constrained device performance. This review comprehensively overviews the latest advancements in ETL materials used in conventional and inverted OPVs. Additionally, it investigates the evolution of dopant materials, emphasizing the need for improved electron mobility, energy level alignment, and surface passivation treatment of the buffer layer and absorber layers in OPVs. Continual studies of transport materials and the potential utilization of doping or multilayer ETLs are suggested as inevitable research toward achieving higher power conversion efficiency and stability in OPV technology. Additionally, identifying optimal ETL materials capable of synergistic interactions remains crucial for sustained progress in renewable energy technology.

Iron complex/graphene oxide hybrid modification of ZnO surface for achieving stable inverted organic photovoltaics

We synthesized a four-coordinated semi-cyclic iron complex and composited it with graphene oxide (GO) to form a hybrid iron complex/GO-based material for organic solar cells (OSC). X-ray diffraction (XRD) analysis showed increased spacing between the GO sheets, indicating that the iron complex successfully intercalated or exfoliated the GO and deposited it on the surface. The as-prepared functionalized graphene oxide (FGO) also exhibits superior dispersion, which can avoid severe aggregation during fabrication. We demonstrated the impact of utilizing FGO as an interlayer to modify the ZnO-based OSC. Through X-ray Photoelectron Spectroscopy (XPS) and Photoluminescence (PL) analysis, we confirmed that FGO effectively reduces oxygen defects on the ZnO surface, leading to a reduction in the rate of carrier recombination and promoting the efficiency (up to 17.04 %) and ambient-stability of PM6:Y6-based OSCs. This discovery holds tremendous potential for advancing the development of high-performance OSCs with exceptional long-term stability.

New Ternary Blend Strategy Based on a Vertically Self-Assembled Passivation Layer Enabling Efficient and Photostable Inverted Organic Solar Cells.

Herein, a new ternary strategy to fabricate efficient and photostable inverted organic photovoltaics (OPVs) is introduced by combining a bulk heterojunction (BHJ) blend and a fullerene self-assembled monolayer (C60 -SAM). Time-of-flight secondary-ion mass spectrometry - analysis reveals that the ternary blend is vertically phase separated with the C60 -SAM at the bottom and the BHJ on top. The average power conversion efficiency - of OPVs based on the ternary system is improved from 14.9% to 15.6% by C60 -SAM addition, mostly due to increased current density (Jsc ) and fill factor -. It is found that the C60 -SAM encourages the BHJ to make more face-on molecular orientation because grazing incidence wide-angle X-ray scattering - data show an increased face-on/edge-on orientation ratio in the ternary blend. Light-intensity dependent Jsc data and charge carrier lifetime analysis indicate suppressed bimolecular recombination and a longer charge carrier lifetime in the ternary system, resulting in the enhancement of OPV performance. Moreover, it is demonstrated that device photostability in the ternary blend is enhanced due to the vertically self-assembled C60 -SAM that successfully passivates the ZnO surface and protects BHJ layer from the UV-induced photocatalytic reactions of the ZnO. These results suggest a new perspective to improve both performance and photostability of OPVs using a facial ternary method.

Mitigating the Efficiency Loss of Organic Photovoltaic Cells Using Phosphomolybdic Acid‐Doped PEDOT:PSS as Hole Transporting Layer

A phosphomolybdic acid (PMA)‐doped poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) hole transporting layer (HTL) is developed to effectively optimize the anode interface of inverted organic photovoltaic (OPV) devices. Since a deep‐lying work function of HTL is in favor of reducing the interfacial barrier for hole transporting, superior power conversion efficiencies (PCE) of 9.22% and 10.8% are achieved in fullerene‐based and nonfullerene‐based devices in inverted architecture. Thus‐prepared OPV devices also exhibit excellent photostability and retain 85% of the initial PCE after 1000 h of irradiation under 100 mW cm−2 irradiation. The overall result suggests the practicability and mitigation of efficiency loss when replacing the conventional PEDOT:PSS with PMA‐doped PEDOT:PSS as HTL to fabricate highly efficient, inverted OPV devices.

Large-Area Nonfullerene Organic Photovoltaic Modules with a High Certified Power Conversion Efficiency

Achieving large-area organic photovoltaic (OPV) modules with reasonable cost and performance is an important step toward commercialization. In this work, solution-processed conventional and inverted OPV modules with an area of 216 cm2 were fabricated by the blade coating method. Film uniformity was controlled by adjusting the fabrication parameters of the blade coating procedure. The influence of the concentration of the solutions of the interfacial materials on OPV module performance was investigated. For OPV modules based on the PM6:Y6 photoactive layer, a certificated power conversion efficiency (PCE) of 9.10% was achieved for the conventional OPV modules based on the TASiW-12 interfacial layer while a certificated PCE of 11.27% was achieved for the inverted OPV modules based on the polyethylenimine (PEI) interfacial layer. As for OPV modules based on a commercially available photoactive layer, PV-X Plus, a PCE of 8.52% was achieved in the inverted OPV modules. A halogen-free solvent, o-xylene, was used as the solvent for PV-X Plus, which makes the industrial production much more environmentally friendly.

Non-Embedded Silver Nanowires/Antimony-Doped Tin Oxide/Polyethylenimine Transparent Electrode for Non-Fullerene Acceptor ITO-Free Inverted Organic Photovoltaics.

Indium tin oxide (ITO)-free solution-processed transparent electrodes are an essential component for the low-cost fabrication of organic optoelectronic devices. High-performance silver nanowires (AgNWs) ITO-free inverted organic photovoltaics (OPVs) usually require a AgNWs-embedded process. A simple cost-effective roll-to-roll production process of inverted ITO-free OPVs with AgNWs as a bottom transparent electrode requires solution-based thick metal oxides as carrier-selective contacts. In this reported study, we show that a solution-processed antimony-doped tin oxide (ATO)/polyethylenimine (PEI) electron-selective contact incorporated on the top of non-embedded AgNWs provides a high-performance ITO-free bottom electrode for non-fullerene acceptor (NFA) inverted OPVs.

18.73% efficient and stable inverted organic photovoltaics featuring a hybrid hole-extraction layer.

Developing efficient and stable organic photovoltaics (OPVs) is crucial for the technology's commercial success. However, combining these key attributes remains challenging. Herein, we incorporate the small molecule 2-((3,6-dibromo-9H-carbazol-9-yl)ethyl)phosphonic acid (Br-2PACz) between the bulk-heterojunction (BHJ) and a 7 nm-thin layer of MoO3 in inverted OPVs, and study its effects on the cell performance. We find that the Br-2PACz/MoO3 hole-extraction layer (HEL) boosts the cell's power conversion efficiency (PCE) from 17.36% to 18.73% (uncertified), making them the most efficient inverted OPVs to date. The factors responsible for this improvement include enhanced charge transport, reduced carrier recombination, and favourable vertical phase separation of donor and acceptor components in the BHJ. The Br-2PACz/MoO3-based OPVs exhibit higher operational stability under continuous illumination and thermal annealing (80 °C). The T80 lifetime of OPVs featuring Br-2PACz/MoO3 - taken as the time over which the cell's PCE reduces to 80% of its initial value - increases compared to MoO3-only cells from 297 to 615 h upon illumination and from 731 to 1064 h upon continuous heating. Elemental analysis of the BHJs reveals the enhanced stability to originate from the partially suppressed diffusion of Mo ions into the BHJ and the favourable distribution of the donor and acceptor components induced by the Br-2PACz.

Significant Stability Improvement of Fullerene Organic Photovoltaics via ZnO Film Modification through the Intermittent Spray Pyrolysis Technique.

Morphological control of the layers within the bulk heterojunction organic photovoltaics (BHJ-OPVs) is a key feature that governs their performance. In the present work, we demonstrate that zinc oxide—ZnO—interlayers sprayed via the intermittent spray pyrolysis technique, employing a low-concentration precursor solution, can yield inverted BHJ-OPVs as efficient as the standard reported ones using the conventional laboratory-scale spin-coating technique. However, we record a pioneer stability behavior of the fabricated inverted fullerene organic photovoltaics (iF-OPVs) with various sprayed ZnO conditions. Thus, after optimizing the sprayed ZnO interfacial layer morphology for the inverted PTB7-Th:PC70BM devices, by carefully inspecting the interdependence between the sprayed ZnO thin film morphology and the figures of merit of the optimized iF-OPVs, we conducted a distinct analysis on the optical and electronic properties of the fresh and degraded devices using external quantum efficiency measurements and impedance spectroscopy. Hence, we showed that the most proper ZnO microstructural morphology was obtained by spraying 25 running cycles (25R). Remarkably, we observed that 25R-ZnO-based iF-OPV devices showed a stunning stability behavior and maintained 85% of their initial power conversion efficiency even after 16.7 months without encapsulation in a dry nitrogen glovebox, demonstrating an excellent shelf stability. Accordingly, this approach might facilitate the scalability of inverted OPVs for industrial production visibility.

Monolayer Hexagonal Boron Nitride: An Efficient Electron Blocking Layer in Organic Photovoltaics

AbstractIn this study, monolayer hexagonal boron nitride (h‐BN) grown via chemical vapor deposition (CVD) as an effective electron blocking layer (EBL) for the organic photovoltaics (OPVs) is proposed. Unexpectedly, it is found that h‐BN can replace the commonly used hole transport layers (HTLs), i.e., molybdenum trioxide (MoO3) and poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in an inverted device architecture. Here, a wet‐transfer technique is employed and a single layer of h‐BN on top of the PV2000:PC60BM blend is successfully placed. Analysis of the bandgap diagram shows that the monolayer h‐BN makes smaller barrier for holes but significantly larger barrier for electrons. This makes the h‐BN effective in blocking electrons while creating a possible path for the holes through tunneling to the electrode, due to the low energy barrier at the PV2000/h‐BN interface. Using h‐BN as an EBL, efficient inverted OPVs are achieved with an average solar‐to‐power conversion efficiency of 6.13%, which is comparable with that of reference devices based on MoO3 (7.3%) and PEDOT:PSS (7.6%) as HTLs. Interestingly, the devices with h‐BN shows great light‐soak stability. The study reveals that the monolayer h‐BN grown by CVD could be an effective alternative EBL for the fabrication of efficient, lightweight, and stable OPVs.

Metal-electrode-free inverted organic photovoltaics using electrospray-deposited PEDOT:PSS and spin-coated HAT-CN exciton blocking layer

Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) films were fabricated using an electrospray deposition (ESD) method. The ESD PEDOT:PSS films exhibited higher PSS content on the surface than spin-coated PEDOT:PSS films, which results in a higher work function. Based on this result, metal-electrode-free inverted organic photovoltaics (OPVs) were fabricated. The ESD PEDOT:PSS was used as the top electrode on the poly(3-hexythiophene-2,5-diyl) (P3HT):[6,6]-phenyl C61 butyric acid methyl ester (PCBM) light-absorbing layer. The power conversion efficiency (PCE) of OPVs was significantly increased with the 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile layer. The improved PCE would be attributed to the suppression of exciton quenching at the P3HT:PCBM and PEDOT:PSS interface.

Antimony doped tin oxide/polyethylenimine electron selective contact for reliable and light soaking-free high performance inverted organic solar cells

We have demonstrated a high-performance low temperature solution processed electron selective contact consisting of 10 at. % antimony doped tin oxide (ATO) and the neutral polymer polyethylenimine (PEI). Inverted organic photovoltaics (OPVs) utilizing ATO/PEI as electron selective contact exhibited high power conversion efficiencies for both the reference P3HT:PCBM and the nonfullerene based P3HT:IDTBR active layer OPV material systems. Importantly, it is shown that the proposed ATO/PEI carrier selective contact provides light soaking-free inverted OPVs. Furthermore, by increasing the thickness of the ATO layer from 40 to 120 nm, the power conversion efficiency of the corresponding inverted OPVs remain unaffected, a parameter which indicates the potential of the proposed ATO/PEI carrier selective contact for high performance light-soaking-free and reliable roll-to-roll printing solutions processed inverted OPVs.

Inverted organic solar cells with non-clustering bathocuproine (BCP) cathode interlayers obtained by fullerene doping

Bathocuproine (BCP) is a well-studied cathode interlayer in organic photovoltaic (OPV) devices, where it for standard device configurations has demonstrated improved electron extraction as well as exciton blocking properties, leading to high device efficiencies. For inverted devices, however, BCP interlayers has shown to lead to device failure, mainly due to the clustering of BCP molecules on indium tin oxide (ITO) surfaces, which is a significant problem during scale-up of the OPV devices. In this work, we introduce C70 doped BCP thin films as cathode interlayers in inverted OPV devices. We demonstrate that the interlayer forms smooth films on ITO surfaces, resulting from the introduction of C70 molecules into the BCP film, and that these films possess both improved electron extraction as well exciton blocking properties, as evidenced by electron-only devices and photoluminescence studies, respectively. Importantly, the improved cathode interlayers leads to well-functioning large area (100 mm2) devices, showing a device yield of 100%. This is in strong contrast to inverted devices based on pure BCP layers. These results are founded by the effective suppression of BCP clustering from C70, along with the electron transport and exciton blocking properties of the two materials, which thus presents a route for its integration as an interlayer material towards up-scaled inverted OPV devices.

Ternary Blend Strategy for Achieving High-Efficiency Organic Photovoltaic Devices for Indoor Applications.

Monomeric perylene diimide (PDI) small molecules display a high absorption coefficient and crystallinity in solid-state thin films due to strong π-π interactions between the molecules. To take advantage of these exciting properties of PDIs, N,N'-bis(1-ethylpropyl)perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) was mixed with a binary blend of PTB7 and PC71 BM to fabricate an efficient ternary blend, which were in turn used to produce organic photovoltaic (OPV) devices well suited to indoor applications (PTB7=poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}), PC71 BM=[6,6]-phenyl-C71 -butyric acid methyl ester). We varied the PC71 BM/EP-PDI weight ratio to investigate the influence of EP-PDI on the optical, electrical, and morphological properties of the PTB7:PC71 BM:EP-PDI ternary blend. Compared with the reference PTB7:PC71 BM binary blend, the ternary blends showed strong optical absorption in the wavelength range in which the spectra of indoor LED lamps show their strongest peaks. The addition of EP-PDI to the binary blend was found to play an important role in altering the morphology of the blend in such a way as to facilitate charge transport in the resulting ternary blend. Apparently, as a result, the optimal PTB7:PC71 BM:EP-PDI-based inverted OPV device exhibited a power conversion efficiency (PCE) of 15.68 %, a fill factor (FF) of 68.5 %, and short-circuit current density (JSC ) of 56.7 μA cm-2 under 500 lx (ca. 0.17 mW cm-2 ) indoor LED light conditions.

Interface modification layers for high-performance inverted organic photovoltaics

Abstract In this study, commercially available BYK dispersants were used as interface modification layers to significantly improve the efficiency of organic photovoltaics. We selected three functional groups containing alcohols and amines from a wide range of BYK dispersants. The cell structure was inverted to the structure of indium tin oxide glass/ZnO/modified layers/PTB7-Th: PC71BM/MoO3/Ag. Because of the functional groups, the dispersants affected the surface energy, work function, and surface roughness of the ZnO layer and altered the morphology of the active layer. The power conversion efficiency of the Disperbyk-181-derived device (9.32% ± 0.13%) was higher than that of the control device (8.31% ± 0.16%). The best efficiency obtained in this study was 9.48% for a fill factor of 72%. This result promotes the commercially available functional materials for inexpensive modified ETLs and might be useful for large-area OPVs and other optoelectronic devices.

Highly efficient flexible organic photovoltaics using quasi-amorphous ZnO/Ag/ZnO transparent electrodes for indoor applications

We report the indoor performance of flexible organic photovoltaic devices utilizing quasi-amorphous ZnO/Ag/ZnO as the transparent conducting electrode. A ZnO/Ag/ZnO electrode with specific thickness values of 40/9/50 nm provides excellent transparent conducting electrode properties with transmittances up to 92% in the visible region, a sheet resistance of 4.8 Ω/sq, and a root-mean squared surface roughness value of 2.1 nm. In addition, the micro-cavity effect and quasi-amorphous structural properties of the ZnO/Ag/ZnO electrode allow further enhanced light absorption and mechanical stability, respectively. Poly (3-hexylthiophene):indene-C60 bisadduct photoactive layer-based inverted organic photovoltaics with the ZnO/Ag/ZnO (40/9/50 nm) electrode yield an averaged power-conversion efficiency of 12.3% under a light-emitting diode lamp with a luminance of 500 lux, which is 20% greater than the power-conversion efficiency value of the reference organic photovoltaics with an indium tin oxide electrode. Furthermore, the same organic photovoltaics on flexible polyethylene terephthalate substrates exhibit excellent mechanical stability (i.e., 92% of the initial power-conversion efficiency value is maintained even after 400 bending cycles with a bending radius of 9.55 mm), with averaged power-conversion efficiency values of 10.2% under the 500-lux light-emitting diode.

Interfacial engineering and optical coupling for multicolored semitransparent inverted organic photovoltaics with a record efficiency of over 12%

Guided by finite-difference time-domain (FDTD) and optical transfer matrix formalism (TMF) simulation, the contradiction between PCE and AVT was solved, and multicolored ST-OSCs with record high efficiency were achieved.

Dual mode OPV-OLED device with photovoltaic and light-emitting functionalities

The rapid development of organic optoelectronic devices such as organic photovoltaics (OPVs) and organic light-emitting devices (OLEDs) is largely attributable to their advantageous properties of their large area, ultrathin thickness, flexiblility, transparency, and solution processability. Herein, we fabricate and characterize a dual mode OPV-OLED device with three-terminal structure comprising a polymer-based bulk-heterojunction inverted OPV unit and a top-emission white phosphorescent OLED unit back-to-back connected via intermediate metal alloy electrode. Sputter-deposited indium tin oxide was used as a transparent cathode of the inverted OPV unit, whereas Ag-doped Al served as a common OPV/OLED anode, allowing the decoupling of electricity generation and light mission functions. Notably, the doping of Al by Ag facilitated the reduction of surface roughness, allowing the above electrode to be used as a common anode and dramatically reducing the leakage current. Finally, the top-emission OLED unit featured an ultrathin layer of Ag-doped Mg as a semitransparent cathode. Thus, successful integration of the OPV-OLED elements results in the decoupling of electricity generation and light emission functionalities, achieving a power conversion efficiency of 3.4% and an external quantum efficiency of 9.9%.

All-Spray-Coated Inverted Semitransparent Organic Solar Cells and Modules

The aim of this study is to demonstrate a fabrication process of all-sprayed inverted organic photovoltaics. We sprayed the blend of poly(3-hexylthiophene-2,5-diyl) and [6, 6] phenyl-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">61</sub> -butyric acid methyl ester as an active layer and zinc oxide prepared by a sol-gel process as an electron transport layer. The highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) as a semitransparent anode and alternative to Ag is sequentially spray-coated. We further utilize nitrogen (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) plasma modification on the active layer for improving the compatibility between two layers in this work. With a combination of tuning the subsequent thermal treatment, the all-sprayed devices with good performance could be obtained. The highest power conversion efficiency (PCE) of 2.90% is achieved by optimizing the N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma and thermal treatment, and the stability test is performed. Moreover, we up-scaled the all-spray-coating process to a module with three cells connected in series, and the PCE of the module is achieved to 2.44%.

Influence of the Hole Transporting Layer on the Thermal Stability of Inverted Organic Photovoltaics Using Accelerated-Heat Lifetime Protocols.

High power conversion efficiency (PCE) inverted organic photovoltaics (OPVs) usually use thermally evaporated MoO3 as a hole transporting layer (HTL). Despite the high PCE values reported, stability investigations are still limited and the exact degradation mechanisms of inverted OPVs using thermally evaporated MoO3 HTL remain unclear under different environmental stress factors. In this study, we monitor the accelerated lifetime performance under the ISOS-D-2 protocol (heat conditions 65 °C) of nonencapsulated inverted OPVs based on the thiophene-based active layer materials poly(3-hexylthiophene) (P3HT), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), and thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTTT) blended with [6,6]-phenyl C71-butyric acid methyl ester (PC[70]BM). The presented investigation of degradation mechanisms focus on optimized P3HT:PC[70]BM-based inverted OPVs. Specifically, we present a systematic study on the thermal stability of inverted P3HT:PC[70]BM OPVs using solution-processed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and evaporated MoO3 HTL. Using a series of measurements and reverse engineering methods, we report that the P3HT:PC[70]BM/MoO3 interface is the main origin of failure of the P3HT:PC[70]BM-based inverted OPVs under intense heat conditions, a trend that is also observed for the other two thiophene-based polymers used in this study.