Boosted efficiency over 18.1% of polymer solar cells by employing large extinction coefficients material as the third component

Over 18.1% Efficiency of Layer-by-Layer Polymer Solar Cells by Enhancing Exciton Utilization near the ITO Electrode

In this work, layer-by-layer (LbL) polymer solar cells (PSCs) are constructed without/with the incorporation of a dissociation strengthening layer (DSL) on the basis of the wide-bandgap donor D18-Cl, as well as the narrow-bandgap nonfullerene acceptor Y6. The efficiency of LbL PSCs is enhanced from 17.62 to 18.15% through introducing a DSL, originating from the enhanced dissociation of D18-Cl excitons near the ITO electrode. Meanwhile, the interfacial energy between D18-Cl and Y6 layers is decreased by incorporating a DSL, which should facilitate molecular interdiffusion for more adequate exciton dissociation in LbL active layers. This work offers a simple and resultful way for realizing power conversion efficiency (PCE) improvement of LbL PSCs with maximized exciton utilization in LbL active layers. The universality of the DSL incorporation strategy on performance improvement can be further confirmed with a boosted PCE from 17.39 to 18.03% or from 17.13 to 17.61% for D18-Cl/L8-BO- or D18-Cl/N3-based LbL PSCs by incorporating a DSL.

Medium Bandgap Nonfullerene Acceptor for Efficient Ternary Polymer Solar Cells with High Open-Circuit Voltage

We have designed a new medium bandgap non-fullerene small-molecule acceptor consisting of an IDT donor core flanked with 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]-thiophene-4-ylidene) malononitrile (TC) acceptor terminal groups (IDT-TC) and compared its optical and electrochemical properties with the IDT-IC acceptor. IDT-TC showed an absorption profile from 300 to 760 nm, and it has an optical bandgap of 1.65 eV and HOMO and LUMO energy levels of -5.55 and -3.83 eV, respectively. In contrast to IDT-IC, IDT-TC has an upshifted LUMO energy level, which is advantageous for achieving high open-circuit voltage. Moreover, IDT-TC showed higher crystallinity and high electron mobility than IDT-IC. Using a wide bandgap D-A copolymer P as the donor, we compared the photovoltaic performance of IDT-TC, IDT-IC, and IDT-IC-Cl nonfullerene acceptors (NFAs). Polymer solar cells (PSCs) using P: IDT-TC, P: IDT-IC, and P:IDT-IC-Cl active layers achieved a power conversion efficiency (PCE) of 14.26, 11.56, and 13.34%, respectively. As the absorption profiles of IDT-IC-Cl and IDT-TC are complementary to each other, we have incorporated IDT-TC as the guest acceptor in the P: IDT-IC-Cl active layer to fabricate the ternary (P:IDT-TC: IDT-IC-Cl) PSC, demonstrating a PCE of 16.44%, which is significantly higher than that of the binary BHJ devices. The improvement in PCE for ternary PSCs is attributed to the efficient exploitation of excitons via energy transfer from IDT-TC to IDT-IC-Cl, suitable nanoscale phase separation, compact stacking distance, and more evenly distributed charge transport.

Improving the Efficiency of Organic Solar Cells with Methionine as Electron Transport Layer

Interface modification is an important way to get better performance from organic solar cells (OSCs). A natural biomolecular material methionine was successfully applied as the electron transport layer (ETL) to the inverted OSCs in this work. A series of optical, morphological, and electrical characterizations of thin films and devices were used to analyze the surface modification effects of methionine on zinc oxide (ZnO). The analysis results show that the surface modification of ZnO with methionine can cause significantly reduced surface defects for ZnO, optimized surface morphology of ZnO, improved compatibility between ETL and the active layer, better-matched energy levels between ETL and the acceptor, reduced interface resistance, reduced charge recombination, and enhanced charge transport and collection. The power conversion efficiency (PCE) of OSCs based on PM6:BTP-ec9 was improved to 15.34% from 14.25% by modifying ZnO with methionine. This work shows the great application potential of natural biomolecule methionine in OSCs.

Promoting the Efficiency and Stability of Nonfullerene Organic Photovoltaics by Incorporating Open-Cage [60]Fullerenes in the Nonfullerene Nanocrystallites

The device efficiency of PM6:Y6-based nonfullerene organic solar cells is fast advanced recently. To maintain organic solar cells (OSCs) with high power conversion efficiency over 16% in long-term operation, however, remains a challenge. Here, a novel non-volatile additive, an open-cage [60]fullerene (8OC₆₀Me), is incorporated into PM6:Y6-based OSCs for high-performance with high durability. With optimized addition of 1.0 wt % 8OC₆₀Me, the PCE value of PM6:Y6/8OC₆₀Me OSCs can be promoted to 16.5% from 15.0%. Most strikingly, such a high PCE performance can maintain nearly 100% for over 500 h at room temperature; at an elevated operation temperature of 80 °C, the PCE can be stabilized above 15.0% after 45 h of operation. Grazing incidence small- and wide- angle X-ray scattering studies reveal improved orientation and crystallinity of Y6 in a fractal-like network structure of PM6 in PM6:Y6/8OC₆₀Me films under in situ annealing, parallel to the enhanced electron mobility. Analysis of charge distributions lines up possible van der Waals interaction between the thienyl/carbonyl moiety of 8OC₆₀Me and difluorophenyl-based FIC-end groups of Y6. This result is of great contrast to those devices with the best-selling PC₆₁BM as the additives─8OC₆₀Me might be of interest to be incorporated into future Y6-based OSCs for concomitantly improved PCE and excellent stability.

High Performance and Stable Organic Solar Cells Fabricated by Y-Series Small Molecular Materials as the Interfacial Modified Layer

The organic solar cell (OSC) has received tremendous consideration for the impressive increased power conversion efficiency (PCE) from 11% to over 18% in the last decade, but another main parameter, the stability, still needs further study to meet the requirements of commercialization. Generally, the inverted structure device shows more stability than the conventional one owing to the structure characteristics, but even so, the performance and stability of the OSC device still need further improvement because of some undesirable contact between the electron transport layer (typically transition metal oxide like ZnO) and the active layer. Here, three Y-series small molecular acceptor materials (Y6, BTP-eC9, and L8-BO) are used as an interfacial modified layer (IML), which could optimize the interfacial characterization of the devices and thus enhance both the performance and stability. As a result, the insertion of the IML improved the interlayer charge transport capacity by passivating the surface of ZnO, leading to the enhancement of short circuit current density (J_SC), fill factor, and PCE of the OSCs. Furthermore, because of the protection of the IML, the OSCs show outstanding stability compared to the control device (without IML), which could maintain 80% performance of the device over 150 h.

Fluorinated Perylene-Diimides: Cathode Interlayers Facilitating Carrier Collection for High-Performance Organic Solar Cells

Organic solar cells (OSCs) have experienced rapid progress with the innovation of near-infrared (NIR)-absorbing small-molecular acceptors (SMAs), while the unique electronic properties of the SMAs raise new challenges in relation to cathode engineering for effective electron collection. To address this issue, two fluorinated perylene-diimides (PDIs), PDINN-F and PDINN-2F, are synthesized by a simple fluorination method, for application as cathode interlayer (CIL) materials. The two bay-fluorinated PDI-based CILs possess a lower lowest unoccupied molecular orbital (LUMO) energy level of ≈-4.0 eV, which improves the energy level alignment at the NIR-SMAs (such as BTP-eC9)/CIL for a favorable electron extraction efficiency. The monofluorinated PDINN-F shows higher electron mobility and better improved interfacial compatibility. The PDINN-F-based OSCs with PM6:BTP-eC9 as active layer exhibit an enhanced fill factor and larger short-circuit current density, leading to a high power conversion efficiency (PCE) exceeding 18%. The devices with PDINN-F CIL retain more than 80% of their initial PCE after operating at the maximum power point under continuous illumination for 750 h. This work prescribes a facile, cost-effective, and scalable method for the preparation of stable, high-performance fluorinated CILs, and instilling promise for the NIR-SMAs-based OSCs moving forward.

Bi and Sn Doping Improved the Structural, Optical and Photovoltaic Properties of MAPbI3-Based Perovskite Solar Cells

One of the most amazing photovoltaic technologies for the future is the organic–inorganic lead halide perovskite solar cell, which exhibits excellent power conversion efficiency (PCE) and can be produced using a straightforward solution technique. Toxic lead in perovskite can be replaced by non-toxic alkaline earth metal cations because they keep the charge balance in the material and some of them match the Goldschmidt rule’s tolerance factor. Therefore, thin films of MAPbI₃, 1% Bi and 0%, 0.5%, 1% and 1.5% Sn co-doped MAPbI₃ were deposited on FTO-glass substrates by sol-gel spin-coating technique. XRD confirmed the co-doping of Bi–Sn in MAPbI₃. The 1% Bi and 1% Sn co-doped film had a large grain size. The optical properties were calculated by UV-Vis spectroscopy. The 1% Bi and 1% Sn co-doped film had small E_g, which make it a good material for perovskite solar cells. These films were made into perovskite solar cells. The pure MAPbI₃ film-based solar cell had a current density (J_sc) of 9.71 MA-cm⁻², its open-circuit voltage (V_oc) was 1.18 V, its fill factor (FF) was 0.609 and its efficiency (η) was 6.98%. All of these parameters were improved by the co-doping of Bi–Sn. The cell made from a co-doped MAPbI₃ film with 1% Bi and 1% Sn had a high efficiency (10.03%).

Ab-initio study of pressure influenced elastic, mechanical and optoelectronic properties of Cd0.25Zn0.75Se alloy for space photovoltaics

The optoelectronic properties of the ternary Cd_0.25Zn_0.75Se alloy are reported under the influence of a high pressure ranging from 0 to 25 GPa, within a modified Becke-Jhonson potential using density functional theory. This alloy has a cubic symmetry, is mechanically stable, and its bulk modulus rises with pressure. It is observed to be a direct bandgap material with a bandgap energy that increases from 2.37 to 3.11 eV with rise in pressure. Pressure changes the optical and electronic properties, causing the absorption coefficient to rise and absorb visible green-to-violet light. The static dielectric constant, along with the static index of refraction, both increase under the influence of pressure. Optical constants, including dielectric constant, optical conductivity, refractive index, extinction coefficient, and reflection, are also investigated and discussed. This DFT forecast explores important research directions for the usage of the CdZnSe semiconductor alloys in the manufacturing of space photovoltaic and optoelectronic devices operating at different pressures.

Tailoring the Morphology's Microevolution for Binary All-Polymer Solar Cells Processed by Aromatic Hydrocarbon Solvent with 16.22% Efficiency

Herein, we report a systematic solvent selection for eco-friendly processed binary all-polymer solar cells (APSCs) with decent power conversion efficiencies (PCEs). Three typical solvents, toluene, o-xylene, and 1,2,4-trimethylbezene, are chosen and compared. The device enabled by o-xylene exhibits the most outstanding PCE of 16.22%, thanks to its favorable morphology, which is to say a well-formed face-on orientation packing motif and a suitable crystallinity and size of phase segregation. Consequently, the solar cell affords sufficient charge generation, as well as efficient and balanced charge transport, which are all positive to pursuing high efficiency. This work offers an understanding of using complete solvent selection as the strategy to realize high-performance devices by sophisticatedly controlling the morphology.