MoO3 Hole Transport Layer Research Articles

Thermally Triggered Interface for Simplified Organic Solar Cells

Organic photovoltaic (OPV) cells are commonly produced by successive printing of four layers on top of a transparent conducting electrode, with the active layer sandwiched in between interlayers followed by the top electrode. Here, the simplification of OPV manufacturing without the need to coat a hole transport layer (HTL) in inverted OPV (n–i–p) is reported. To ensure the required hole selectivity, thermally trigged molecules are directly blended in the active layer during device casting. Following thermal annealing of the complete devices, organosulfur molecules self‐assembled to form a hole–transporting interface between the silver top electrode and the active layer, thereby enabling working devices. Device optimization is performed by varying the concentration of these molecules and the thermal annealing conditions. The performances of the simplified devices approach those of control devices with vacuum‐evaporated MoO3 HTLs. The solar cells exhibit very encouraging thermal and photostabilities. This work opens the route to high efficiency, simplified, and low‐cost organic solar cells.

Performance Enhancement of SnS Solar Cell with Tungsten Disulfide Electron Transport Layer and Molybdenum Trioxide Hole Transport Layer

Herein, a new heterojunction photovoltaic (PV) device is designed by incorporating molybdenum trioxide (MoO3) as a hole transport layer (HTL), tin sulfide (SnS) as an absorber, and tungsten disulfide (WS2) as an electron transport layer (ETL). The PV outputs of the proposed thin‐film solar cell (TFSC) of Ni/MoO3/SnS/WS2/FTO/Al are investigated using the widely used solar cell simulator (SCAPS‐1D). It is found that the SnS TFSC with suitable band alignments at both the SnS/WS2 and MoO3/SnS interfaces gives better photoconversion efficiency than the conventional one. To optimize the material properties, the performance parameters, including open‐circuit voltage (Voc), short‐circuit current density (Jsc), fill factor (FF), and efficiency, have been calculated by varying the influences of the material's thickness, doping concentration, bulk and interface defect densities, operational temperature, and work function of back‐contact. At optimized thicknesses of 0.1 μm for MoO3 HTL and 1.0 μm for SnS absorber, the efficiency is estimated to be 30.42% with Voc of 1.02 V, Jsc of 34.38 mA cm−2, and FF of 87.04% for the suggested TFSC. These outcomes imply that the nontoxic MoO3 and WS2 materials can be applied as HTL and ETL into the inexpensive, highly efficient, and environmentally friendly SnS‐based PV cell.

Revealing the high-performance of a novel Ge-Sn-Based perovskite solar cell by employing SCAPS-1D

In this study, a novel Ge-Sn based perovskite solar cell (PSC) with the structure FTO/WS2/ FA0.75MA0.25Sn0.95Ge0.05I3/MoO3/Ag has been designed and thoroughly analyzed employing SCAPS-1D. Drawing attention from the work of Ito et al where a similar perovskite-based PSC displayed a poor performance of ∼ 4.48% PCE, in which a large conduction band offset (CBO) acts as a critical factor contributing to interfacial recombination and device deterioration. To address this issue, we presented WS2 as an electron transport layer (ETL) along with MoO3 as a hole transport layer (HTL), both possessing compatible CBO and valence band offset (VBO) with perovskite material. Through systematic simulations and optimizations, remarkable improvements in the PSC’s performance have been acquired, getting a power conversion efficiency (PCE) of 18.97%. The optimized structure involved a 50 nm MoO3 HTL, 350 nm FA0.75MA0.25Sn0.95Ge0.05I3 light-harvesting layer (LHL), and a 50 nm WS2 ETL. Bulk defect densities for the LHL and ETL were optimized to 1 × 1015 cm−3 and 1 × 1018 cm−3, respectively, significantly superior values than that of reported value in the literature. Particularly, the tolerable defect density of ETL has increased 1000 times more than the published literature. The interfacial tolerable trap density for MoO3/perovskite increased from 1 × 1014 cm−2 to 1 × 1016 cm−2. The study also explored the impact of defects on quantum efficiency, revealing a severe negative influence beyond a perovskite bulk defect density of 1 × 1017 cm−3. Light intensity analysis demonstrated a correlation between incident light reduction and device performance decay. Capacitance–Voltage (C-V) and Mott–Schottky (M-S) have been analyzed during the study. Finally, the total recombination of the optimized device concerning thickness has been analyzed along with the dark J-V characteristics. The comprehensive insights gained from this work are anticipated to accelerate the fabrication of mixed Ge-Sn based PSCs with improved efficiency, paving the way for commercialization in the photovoltaic industry.

Spray-Coated MoO3 Hole Transport Layer for Inverted Organic Photovoltaics.

This study focuses on the hole transport layer of molybdenum trioxide (MoO3) for inverted bulk heterojunction (BHJ) organic photovoltaics (OPVs), which were fabricated using a combination of a spray coating and low-temperature annealing process as an alternative to the thermal evaporation process. To achieve a good coating quality of the sprayed film, the solvent used for solution-processed MoO3 (S-MoO3) should be well prepared. Isopropanol (IPA) is added to the as-prepared S-MoO3 solution to control its concentration. MoO3 solutions at concentrations of 5 mg/mL and 1 mg/mL were used for the spray coating process. The power conversion efficiency (PCE) depends on the concentration of the MoO3 solution and the spray coating process parameters of the MoO3 film, such as flow flux, spray cycles, and film thickness. The results of devices fabricated from solution-processed MoO3 with various spray fluxes show a lower PCE than that based on thermally evaporated MoO3 (T-MoO3) due to a limiting FF, which gradually increases with decreasing spray cycles. The highest PCE of 2.8% can be achieved with a 1 mg/mL concentration of MoO3 solution at the sprayed flux of 0.2 mL/min sprayed for one cycle. Additionally, S-MoO3 demonstrates excellent stability. Even without any encapsulation, OPVs can retain 90% of their initial PCE after 1300 h in a nitrogen-filled glove box and under ambient air conditions. The stability of OPVs without any encapsulation still has 90% of its initial PCE after 1300 h in a nitrogen-filled glove box and under air conditions. The results represent an evaluation of the feasibility of solution-processed HTL, which could be employed for a large-area mass production method.

Evaluating the performance of efficient Cu2NiSnS4 solar cell—A two stage theoretical attempt and comparison to experiments

In this work, copper nickel tin sulfide (Cu2NiSnS4) as an encouraging alternative absorber for thin-film photovoltaic devices is explored. Here, the Cu2NiSnS4 (CNTS) absorber-based heterojunction solar cell is designed through a two-stage theoretical approach using Solar Cell Capacitance Simulator in one-dimension (SCAPS-1D). Initially four different hole transport materials (MoO3, SnS, NiOx, and PEDOT.PSS) are incorporated at the back interface in experimentally configured Au/Cu2NiSnS4/ZnS/ZnO/ITO cell to boost the device outputs. The MoO3 semiconductor is anticipated as a hole transport layer (HTL) in the heterojunction Ni/MoO3/Cu2NiSnS4/ZnS/ZnO/ITO solar configuration. It is revealed that an appropriate band alignment can be formed at MoO3/Cu2NiSnS4 interface with less interfacial defects among other HTLs with CNTS absorber, thus improving the solar cell outputs. Efficiency is increased from 2.71% to 8.79% for the proposed CNTS-based solar cell. Further optimization is accomplished concerning thickness, defect states, and doping density of the various materials utilized in the heterojunction structure. Defect characteristics at the MoO3/Cu2NiSnS4 and Cu2NiSnS4/ZnS interfaces are also evaluated and optimized to boost the conversion efficiency significantly. Moreover, the effects of operating temperature and rear electrode work function on the outputs of the designed solar device are studied. The aforesaid two-stage optimization yields efficiency of 12.46% with VOC of 1.23 V, JSC of 12.66 mA/cm2, and FF of 79.78%. Therefore, these findings will facilitate the scientific communities to further progress an economical and extremely efficient CNTS-based solar device with a promising MoO3 HTL.

Tuning the surface states by in-situ Zr/Hf co-doping and MoO3 hole transport layer modification for boosting photoelectrochemical performance of hematite photoanode

Hematite (α-Fe2O3) is a potential photoanode material for photoelectrochemical (PEC) water splitting; nevertheless, its PEC performance is constrained by substantial bulk and surface charge recombination rates. Herein, the effect of in-situ Zr/Hf dual-ion doping and the MoO3 hole transport layer (HTL) on regulating the surface states of α-Fe2O3 photoanodes for effective water oxidation is investigated. The co-doping improves bulk properties by enhancing the electrical conductivity, thereby facilitating hole transfer via intermediate surface states (i-SS). Furthermore, the MoO3 HTL passivates the recombination surface states (r-SS), thus alleviating the Fermi level pinning, resulting in an improved open-circuit photovoltage. As a result, a novel Zr/Hf-HT:MoO3 photoanode attains a photocurrent density of 2.34 mA cm−2 at 1.23 V vs. RHE (1.23 VRHE), which is 123% higher than that of Bare-HT. The Zr/Hf-HT:MoO3 photoanode achieves 86 and 61.3% of surface charge separation and charge transfer efficiencies at 1.23 VRHE, respectively, representing 26 and 100% enhancements over those of Bare-HT. Lastly, the FeNi(OH)x cocatalyst coated Zr/Hf-HT:MoO3 photoanode reaches a photocurrent density of 2.62 mA cm−2 at 1.23 VRHE with 98% stability and generates 47.8 and 22 μmol h−1 of H2 and O2 gases, respectively.

Photoelectric Conversion and Device Stability of PM6:PY-IT Solar Cells Based on a Water Solution-Processed MoO3 Hole Transport Layer.

To enhance the power conversion efficiency (PCE) and stability of all-polymer solar cells (all-PSCs), a new precursor solution based on an in situ chemical reaction of nanomolybdenum powder (Mo), hydrogen peroxide (H2O2), and ammonia (NH3·H2O) was developed for preparing a MoO3 hole transport layer (HTL) for all-PSCs. The results showed that the PCE and stability of PM6:PY-IT solar cells based on the MoO3 HTL were better than those based on a PEDOT:PSS layer. To further understand the relationship between the HTL and the device performance, ultrafast photophysical processes of all-PSCs based on different HTLs were contrastively analyzed. Our research indicated that the micromorphology of active layers could be influenced by the interfacial layer material, consequently determining the photoelectric conversion process of all-PSCs. The MoO3-based all-PSCs had longer charge lifetime, higher charge mobility, and lower charge recombination characteristics compared with the devices based on the PEDOT:PSS layer during the operation time. As a result, the MoO3-based PM6:PY-IT solar cells achieved an initial PCE of 15.2%, and they still maintained more than 80% of their initial efficiency after 1000 h.

Dramatic improvement in the stability and mechanism of high-performance inverted polymer solar cells featuring a solution-processed buffer layer.

In this study, we demonstrate inverted PTB7:PC71BM polymer solar cells (PSCs) featuring a solution-processed s-MoO3 hole transport layer (HTL) that can, after thermal aging at 85 °C, retain their initial power conversion efficiency (PCE) for at least 2200 h. The T80 lifetimes of the PSCs incorporating the novel s-MoO3 HTL were up to ten times greater than those currently reported for PTB7- or low-band-gap polymer:PCBM PSCs, the result of the inhibition of burn-in losses and long-term degradation under various heat-equivalent testing conditions. We used X-ray photoelectron spectroscopy (XPS) to study devices containing thermally deposited t-MoO3 and s-MoO3 HTLs and obtain a mechanistic understanding of how the robust HTL is formed and how it prevented the PSCs from undergoing thermal degradation. Heat tests revealed that the mechanisms of thermal inter-diffusion and interaction of various elements within active layer/HTL/Ag electrodes controlled by the s-MoO3 HTL were dramatically different from those controlled by the t-MoO3 HTL. The new prevention mechanism revealed here can provide the conceptual strategy for designing the buffer layer in the future. The PCEs of PSCs featuring s-MoO3 HTLs, measured in damp-heat (65 °C/65% RH; 85 °C per air) and light soaking tests, confirmed their excellent stability. Such solution-processed MoO3 HTLs appear to have great potential as replacements for commonly used t-MoO3 HTLs.

Thermoplastic elastomer enhanced interface adhesion and bending durability for flexible organic solar cells

Stable interface adhesion and bending durability of flexible organic solar cells (FOSCs) is a basic requirement for its real application in wearable electronics. Unfortunately, the device performance always degraded during continuous bending. Here, we revealed the weak interface adhesion force between MoO3 hole transporting layer (HTL) and the organic photoactive layer was the main reason of poor bending durability. The insertion of an interface bonding layer with a thermoplastic elastomer, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) effectively improved the interface adhesion force of MoO3 HTL and the active layer and decreased the modulus, which ensured higher than 90% of the initial efficiency remaining after 10000 bending. Meanwhile, the FOSCs gave an efficiency of 14.18% and 16.15% for the PM6:Y6 and PM6:L8-BO devices, which was among the highest performance of FOSCs. These results demonstrated the potential of improving the mechanical durability of FOSCs through thermoplastic elastomer interface modification.

Performance enhancement of an organic photodetector enabled by NPB modified hole transport layer

Transport layers are extremely important for organic photodetectors (OPDs) due to their effective role in improving the charge selectivity at the contacts, thus leading to high photoresponse and low dark current. The quintessential hole transport layer (HTL), e.g. MoO3, is suffering from the work function instability caused by the preparation process and the evolution in external environment. In this paper, we introduce an N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) interfacial layer to modify MoO3 HTL. At an optimized NPB thickness of 20 nm, the photocurrent (J p) density of the device increases by 19%, thus the responsivity and external quantum efficiency are raised to 0.44 A W−1 and 75% at 725 nm. Besides, owing to the suppressed dark current, the optimized device showcases an enhanced specific detectivity of over 1011 Jones in the range of 460–750 nm (under negative bias). This achievement is assigned to the improvement in transport and collection efficiency of holes. The study provides a feasible method of HTL modification to improve the performance of OPDs.

Facile solution-processed molybdenum oxide as hole transporting material for efficient organic solar cell

The large energy barrier in hole extraction still remains a great challenge in developing hole transporting layer (HTL) materials for organic solar cells (OSCs). Thus, solution-processed HTL materials with excellent hole collection ability and good compatibility with large-area processing technique are strongly desired for OSCs. Herein, we developed a cost-effective and solution-processed MoO3 HTL for efficient OSCs. By adding a small amount of glucose as reducing reagent into the ammonium molybdate precursor solution, a deeply n-doped MoO3, namely G:Mo, was prepared through the sol–gel method. Compared to pristine MoO3, the conductivity of G:Mo was enhanced by two orders of magnitude, which greatly improved the hole collection ability of the HTL. OSCs with G:Mo can exhibit comparable PCE to the PEDOT:PSS device. Using PBDB-TF:BTP-eC9 as the active layer, a PCE of 17.1% is obtained for the device, which is the highest PCE value for OSC using a solution-processed MoO3 HTL. More importantly, G:Mo is well compatible with the blade-coating processing. The OSC using a blade-coated G:Mo showed almost no PCE loss as compared to the device with spin-coated G:Mo HTL. The results from this work indicate that G:Mo is a promising HTL material for the practical production of OSCs.

New electron donor in planar heterojunction: optimization of the cells efficiency through the choice of the hole-extracting layer

Due to their light weight, flexibility and semi-transparency the organic photovoltaic cells play an important role for solar conversion photovoltaic (OPV). To achieve good performances, both donor and acceptor materials in OPVs need to have good extinction coefficients, high stabilities and good film morphologies. Since the donor plays a critical role as the absorber to solar photon flux, donor materials require wide optical absorption to match the solar spectrum. In this work the couple ED/EA in planar heterojunction was Tetracyano 4,4'-bis(9Hcarbazol-9-yl) biphenyl (TCC)/fullerene (C60). Optimum results are obtained when MoO3 alone is used as Hole Transporting Layer (HTL). The J/V characteristics do not exhibit S-shaped curves up to a TCC layer thickness of 15 nm, while they did when the HTL includes CuI. Theoretical study, complementary to the experimental study, shows that in the case of S-shaped curve the cell behaves as if it was made up of 2 diodes, one of which would be opposed to the flow of the photogenerated current. In the case of MoO3 HTL, i.e; without shaped curve, the optimum thickness is 13 nm, giving an efficiency η = 2.30% with V oc = 0.9 V, J sc = 5.17 mA/cm2 and FF = 49%.

Ga-doped ZnO nanorod scaffold for high-performance, hole-transport-layer-free, self-powered CH3NH3PbI3 perovskite photodetectors

The use of aligned one-dimensional nanostructures as scaffolds in organic-inorganic hybrid perovskite photodetectors (PDs) has attracted significant attention due to their large surface area-to-volume ratio and efficient electron transport capability in the radial direction. Here, we report CH3NH3PbI3 (MAPbI3) perovskite photodetectors (PDs) with Ga-doped ZnO nanorods (GZO NRs), prepared by the water bath method, as a scaffold-structure electron transport layer (ETL). Our MoO3 hole transport layer (HTL) based perovskite PDs using GZO NRs as a scaffold showed a larger light/dark current (Iph/Idark) ratio, higher responsivity and detectivity than those of the undoped ZnO NRs/MAPbI3 devices at zero bias. These enhancements are attributed to the incorporation of Ga atoms into the ZnO NRs, which reduce the density defect states of ZnO NRs and improves the performance of MAPbI3 perovskite PDs. In addition, by taking advantage of the GZO NRs scaffold structure, a HTL-free perovskite PD was prepared by using graphite electrodes. The graphite-connected device shows self-powered PD performances with an Iph/Idark ratio of ~2.5 × 103, responsivity of above 0.3 A/W and detectivity of 1.3 × 1012 Jones, all of which are comparable with those of MoO3 HTL based perovskite PDs.

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.

Power conversion efficiency enhancement of polymer solar cells using MoO3/TFB as hole transport layer

In this paper, we report a simple method to increase the power conversion efficiency (PCE) of the polymer solar cells based on poly(3-hexylthiophene) and [6, 6]-phenyl-C61-butyric acid methyl ester derivatives blended active layer. The approach includes using a molybdenum oxide (MoO3) and Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) composites as the hole transport layer (HTL). Compared with that of the device with bare MoO3 HTL, the maximum 39 % increased of PCE is obtained when MoO3/TFB composites as the HTL in the devices. The device with MoO3/TFB shows the best performance with a PCE of 3.70 %, an open-circuit voltage of 0.58 V, and a short-circuit current density of 11.39 mA/cm2. The intrinsically mechanisms behind PCE increased are due to the improvement in the interface layer morphology and the more appropriately energy level of the cells.

Solution-processed MoO3:PEDOT:PSS hybrid hole transporting layer for inverted polymer solar cells.

Solution-processed organic-inorganic hybrids composing of MoO3 nanoparticles and PEDOT:PSS were developed for use in inverted organic solar cells as hole transporting layer (HTL). The hybrid MoO3:PEDOT:PSS inks were prepared by simply mixing PEDOT:PSS aqueous and MoO3 ethanol suspension together. A core-shell structure was proposed in the MoO3:PEDOT:PSS hybrid ink, where PEDOT chains act as the core and MoO3 nanoparticles connected with PSS chains act as the composite shell. The mixing with PEDOT:PSS suppressed the aggregation of MoO3 nanoparticles, which led to a smoother surface. In addition, since the hydrophilic PSS chains were passivated through preferentially connection with MoO3, the stronger adhesion between MoO3 nanoparticles and the photoactive layer improved the film forming ability of the MoO3:PEDOT:PSS hybrid ink. The MoO3:PEDOT:PSS hybrid HTL can therefore be feasibly deposited onto the hydrophobic photoactive polymer layer without any surface treatment. The use of the MoO3:PEDOT:PSS hybrid HTL resulted in the optimized P3HT:PC61BM- and PTB7:PC61BM-based inverted organic solar cells reaching highest power conversion efficiencies of 3.29% and 5.92%, respectively, which were comparable with that of the control devices using thermally evaporated MoO3 HTL (3.05% and 6.01%, respectively). Furthermore, less HTL thickness dependence of device performance was found for the hybrid HTL-based devices, which makes it more compatible with roll-to-roll printing process. In the end, influence of the blend ratio of MoO3 to PEDOT:PSS on photovoltaic performance and device stability was studied carefully, results indicated that the device performance would decrease with the increase of MoO3 blended ratio, whereas the long-term stability was improved.

Electroluminescent Quantum Dot Light-Emitting Diodes with ZnO and MoO<sub>3</sub> Carrier Transport Layers

In this article, the quantum dot (QD) light emitting diodes (QDLEDs) with ZnO electron transport layer (ETL) and MoO3 hole transport layer (HTL) were demonstrated. The ZnO ETL was fabricated by sol-gel method. To achieve balanced electron and hole injection, hole transport materials including 4,4'-di(N-carbazolyl)biphenyl (CBP) and MoO3 were also adapted. The device structure can be simply depicted as indium tin oxide (ITO)/ZnO/Cs2CO3/QD/CBP/MoO3/Au. It was found that the Cs2CO3 played an important role to facilitate radiative recombination and reduce the leakage current due to the poor quality of sol-gel fabricated ZnO thin film. Via inserting an annealed Cs2CO3 buffer layer with proper thickness, red-emitting QDLEDs with low luminance turn-on voltage of 4.1 V and luminance larger than 100 cd/m2 could be obtained. With our demonstration, QDLEDs with ZnO ETL can be a promising device structure for realizing QDLED’s commerizing.

Enhancing the stability of polymer solar cells by improving the conductivity of the nanostructured MoO3 hole-transport layer

This article demonstrates improvements in the operational stability of organic solar cells (OSCs) by taking advantage of the relationship between oxygen stoichiometry and conductivity in nanostructured metal oxide semiconductors (n-MOS). OSCs in the inverted device configuration of ITO/Ca/P3HT:PCBM/MoO3/Ag were employed in the present study. A high degree of oxygen defects were introduced in the hole-conducting MoO3 layer by annealing the devices under vacuum (≥10(-5) mbar) for nominal temperature (120 °C) and time (10 min). The above devices had much higher operational stability, when tested following the ISOS-D-1 (shelf) protocol, than control devices annealed conventionally, i.e., in nitrogen atmosphere. Employing current-voltage measurement as functions of temperature and photon flux, we show that the devices annealed under vacuum have a lesser density of traps than those annealed in nitrogen. The lesser trap density is shown to be beneficial in reducing the rate of electron recombination thereby increasing the operational stability of the corresponding device. A number of experiments were undertaken to show that the difference in the operation stability of the device results from the difference in conductivity of the nanostructured MoO3 hole transporting layer. The charge extraction by linear increasing voltage spectroscopy shows that charges are relaxed at the trap states in the device annealed in nitrogen whereas they are efficiently transported in the other device. We identify that building up of an interfacial potential barrier as a result of the charge relaxation at the trap states and the corresponding chemical changes in the devices annealed conventionally is the source of degradation of the device performance over time. To our knowledge, this is the first report that successfully overcomes hole-conductivity induced degradation in organic solar cells.

Efficient Organic Photovoltaic Cells Using Hole-Transporting MoO3 Buffer Layers Converted from Solution-Processed MoS2 Films

We introduce a new method to fabricate a MoO3 hole-transporting layer for organic photovoltaic cells (OPVs). We fabricated a MoS2 film from its solution and converted it to MoO3. MoS2 has a lamellar crystal structure similar to graphite, and it can be exfoliated into monolayer MoS2 dispersible in water. Li atoms were first intercalated into van der Waals gaps of MoS2, and the compound was immersed in water to generate H2 bubbles, which broke the van der Waals bond between adjacent MoS2 layers. The produced solution of MoS2 was spin-casted on an indium tin oxide substrate, and the film was oxidized by ozone. On the converted MoO3 hole-transporting layer, an organic photoconversion layer was fabricated by spin-casting a poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) composite solution. Fabricated OPVs revealed a power conversion efficiency as large as 3.14%, which was superior to that of P3HT/PCBM OPV with a poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole-transporting layer.

An inverted organic solar cell with an ultrathin Ca electron-transporting layer and MoO3 hole-transporting layer

An inverted organic solar cell based on poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) was fabricated with an ultrathin Ca electron-transporting layer and MoO3 hole-transporting layer. The 1 nm Ca on indium tin oxide (ITO) electrode modifies the work function of ITO suitable for electron extraction. An appropriate thickness of MoO3 hole extraction layer is also essential to effectively prevent exciton quenching at the Ag anode, yet not introduce much voltage loss and series resistance. The optical field distribution across the active layer was also simulated to discuss the effect of MoO3 thickness on the photocurrent. The maximum power conversion efficiency obtained was 3.55% under simulated 100 mW/cm2 (AM 1.5G) solar irradiation.