For a long period, organic solar cells (OSCs) have attracted attention due to the potentials in applicability with properties such as flexibility, light weight, and semi-transparency. The first study is aimed at the repeatable and large unit fabrication, so that the spin coating process is replaced by the sheet coating process.
Working Mechanism of Organic Solar Cells
They move to the donor and acceptor interface to separate into free charge carriers holes and electrons with the help of excess energy originating from the energy level gap of the donor and acceptor. After separation, the charge carriers are transported to the electrode along the donor and acceptor domain phases by hopping transport, then extracted and collected, generating a current.
Device Structure and Characterization of Organic Solar Cells
Therefore, the highest current that can be obtained from a solar cell is the short-circuit current. The fill factor (FF) is a term that defines the maximum power in relation to JSC and VOC from a solar cell. FF can be expressed by Eq.
Recombination under Operation of Organic Solar Cells
To compare the performance, you should keep the same condition of AM 1.5 at a temperature of 25°C because the performance of the device can be affected by the intensity and temperature of the light. As shown in Figure 1.4, nonmining recombination can be further divided into trap-assisted recombination and bimolecular recombination.
Fabrication Methods of Organic Solar Cells
It works effectively for laboratory-scale procedures that require precise film thickness. Blade coating is one of the commonly used substitutes for spin coating with rolling process compatibility (R2R), which is the right process for mass production.
Evaporation Driven Flows
Induced Marangoni flow in leaf coating process for optimized active layer morphology in organic solar cells. Roles for side chain orientation and development of green colored efficient semitransparent organic solar cells. Fused benzothiadiazole: A building block for organic n-type acceptor to achieve high performance organic solar cells.
High efficiency organic solar cells with low loss without recombination radiation and low energy disorder. Effect of symmetry breaking of non-fullerene acceptors for efficient and stable organic solar cells. Highly efficient and stable all-polymer solar cells enabled by near-infrared isomerized polymer receivers.
High efficiency organic solar cells based on asymmetric acceptors bearing a 3D shape-persistent terminal group. J.; Wang, E., High Performance All-Polymer Solar Cells by Synergistic Effects of Fine-tuned Crystallinity and Solvent Annealing.
Induced Marangoni Flow in Blade-Coating Process for Optimized Active-Layer Morphology
Results and Discussion
Chlorinated thiophene end groups for highly crystalline alkylated nonfullerene acceptors toward efficient organic solar cells. Selenium heterocyclic electron acceptor with low Urbach energy for cast high-performance organic solar cells. Nonfullerene small molecule acceptors with a carbazole core for high voltage open-circuit organic solar cells.
Optimization of the charge carrier and light management of nonfullerene acceptors for efficient organic solar cells with small nonradiative energy losses. Fine tuning of energy levels via asymmetric end groups enables polymer solar cells with efficiencies in excess of 17%. Morphological stabilization in organic solar cells via a fluorene-based cross-linker for improved efficiency and thermal stability.
Fine tuning the dipole moment of asymmetric non-fullerene acceptors, enabling efficient and stable organic solar cells.
Conclusion
Huang, F.; Cao, Y., Morphology optimization via side chain engineering enables all-polymer solar cells with excellent fill factor and stability.
Optimization and Morphology Analysis of Nonfullerene Acceptors with Ester Functionalized
Results and Discussion
The absorption spectra are plotted in Figure 3.1 b-c and the detailed optics and parameters are summarized in Table 3.1. The energy level diagrams of three NFAs and their corresponding CV curves are shown in Figure 3d. The J-V characteristics of the devices measured at the intensity of 100 mW cm-2 under AM 1.5G illumination, shown in Figure 3.2 a; the detailed one.
The photocurrent density (Jph) versus effective voltage (Veff) curve was studied to investigate the exciton dissociation and charge collection ability, as shown in Figure 4c and the efficiencies are summarized in Table S1. As shown in Figure 3.3 a-c, all blended films exhibit the fibril textures with the low mean square surface roughness (Rq) values of nm and the flower-like D/A phase separation characteristics. In particular, the PM6:BTP-Est2F blend exhibits the lowest aggregation behavior and the best interpenetrating network, as supported by the highest miscibility between donor and acceptors, determined via Flory-Huggins interaction parameter (χ) values.64 So we can deduce from this that the asymmetric termination of EstIC with 2FIC is advantageous to form the favorable mixture morphology for the efficient intermolecular charge transport.
GIWAXS analyzes were conducted to analyze the crystalline feature and molecular stacking properties of the pure films and the mixed films containing PM6. The line-cut profiles and their associated parameters are shown in Figure Xc and Table 3.3.
Conclusion
Guest-oriented non-fullerene acceptors for ternary organic solar cells with over 16.0% and 22.7% efficiency under single-sun and indoor light. Side chain isomerization on an n-type organic semiconductor ITIC acceptor makes 11.77% high efficiency polymer solar cells. Non-fullerene acceptors with branched side chains and improved molecular packing to exceed 18% efficiency in organic solar cells.
Subtle molecular tailoring induces significant morphological optimization enabling over 16% efficiency organic solar cells with efficient charge generation. Changing the positions of chlorine and bromine substitution on the end group enables high performance acceptor and efficient organic solar cells. Highly efficient polymer solar cells with effective hole transfer at zero Highest occupied molecular orbital displacement between methylated polymer donor and brominated acceptor.
Effect of third component on efficiency and stability in ternary organic solar cells: More than a simple superposition. Highly efficient small molecule ternary solar cells with a hierarchical morphology enabled by synergizing fullerene and non-fullerene acceptors. Towards improved lifetimes of organic solar cells under thermal stress: Substrate-dependent morphological stability of PCDTBT:PCBM films and devices.
Highly efficient, thermal-annealing-free organic solar cells based on an asymmetric acceptor with improved thermal and air stability.
Motivation and Research Direction
Effect of substituted acceptor units in naphthalene diimide-based random copolymer acceptors on morphology for improved fill factors. Here, four new polymeric acceptors were synthesized by replacing 10% of the centrosymmetric structure of the acceptor unit, NDI, with axisymmetric structures of 5-(2-hexyldecyl)-4H-thieno[3,4-c]pyrrole-4,6(5H) )- dione (TPD), 1,3-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione (BDD) and asymmetric structures of thieno[3, 4-b ]thiophene-2-carboxylic acid, 3-fluoro, 2-ethylhexyl ester (2FQ), 6,7-difluoro-2-((2-hexyldecyl)oxy)quinoxaline (TT) to analyze changes in material properties and morphology films and their relationship. The tilt angle and dipole moments of each polymer acceptor were evaluated by DFT, indicating their intrinsic characteristics.
The morphological analysis was performed via AFM and TEM, which provided further insights into the aggregation, surface topology and phase separation. Overall, the random copolymer acceptors with less symmetric accepting units showed the improved FF, compared to the N2200 base devices. The morphological analysis showed an almost similar trend of more favorable mixtures than N2200, supporting the photovoltaic performance result.
Results and Discussion
The optical properties of the copolymer acceptors as a solution in the film state and a solution in chloroform were investigated by UV-vis absorption spectroscopy shown in Figure 4.1. Compared to that of the pure N2200 film, the normalized absorption spectrum of the random copolymer acceptors results in either the improved ICT with the asymmetric structure with altered acceptor units, or the reduced π-π* interaction from the higher planarity small. Furthermore, the relatively high LUMO energy levels of P(NDI-2FQ10) may be a reason for the higher VOC, which is from the gap between the HOMO level of a donor and the LUMO level of an acceptor.
APSCs were fabricated to evaluate the device performance of the synthesized copolymer acceptor-based devices, which have a conventional configuration. The photovoltaic performance of the APSCs is significantly influenced by the morphology of the photoactive layer.44 To further understand the effect of partially substituted naphthalene diimide-based random copolymer acceptors on the morphology in BHJ, the composite films were studied by AFM and TEM. In addition, the miscibility between PBDB-T and the random copolymer acceptors was estimated by the χ values using the equation of χ ∝ (√γ𝐷− √𝛾𝐴)2, where γ𝐷 and 𝛾𝐴 are the surface energy of the donor or acceptor is (𝝛 or accept) .
45-47 The surface energy was measured with the contact angle of water and ethylene glycol in neat films as shown in Figure 4.4 and the corresponding 𝛾 values were summarized in Table 4.2. However, in the case of P(NDI-TT10), excessive mixing between donor and acceptor may be a reason for increased charge-carrier recombination.
Conclusion
To evaluate the charge transport properties, the hole and electron mobility of the mixed films was measured by the SCLC method.54 The configurations of Ag/MoO3/Active layer/PEDOT:PSS/ITO for hole-only devices and Ag/PDINO/Active low/ZnO/ITO for electron-only devices were fabricated. The PBDB-T:P(NDI-BDD10) mixture showed the most balanced μe/μh ratio of holes and electron mobility of 0.991, which exists well with higher JSC and FF observed in photovoltaic parameters55-57.
Ying, L.; Cao, Y., Overcoming efficiency loss of bulk polymer solar cells with an asymmetric alkyl side chain of n-type polymer based on naphthalene diimide. J.; Yan, H.; Li, Y.; Min, J., Achieving greater than 17% efficiency of ternary polymer solar cells with two well-matched polymer receivers. Ying, L.; Liu, F.; Li, N.; Huang, F.; Cao, Y., Morphology optimization via donor polymer molecular weight tuning enables all-polymer solar cells with simultaneously improved performance and stability.
R.; Guo, X., High-performance n-type polymer-activated polymer solar cells with a narrow bandgap down to 1.28 eV. R., Recent advances in n-type polymers for all-polymer solar cells. Kim, Y.-H., Synergistic Engineering of Side Chains and Axis Region Regularity of Polymer Acceptors for High-Performance All-Polymer Solar Cells with 15.1% Efficiency. Wei, K.-H., Simultaneous use of wide- and small-angle X-ray techniques to analyze nanometer-scale phase separation in polymer heterojunction solar cells.
The SCLC mobilities were calculated using the Mott-Gurney equation, J = 9εrε0μV2/8L3, where εr is the relative dielectric constant of the organic semiconductor, ε0 is the free-space permittivity, μ is the zero-field mobility, L is the active layer thickness, and V = Vapplied – Vbuilt-in – V-series resistance (Vbi value is 0.2 V and 0 V for hole-only devices and electron-only devices, respectively), where Vapplied is the applied voltage, and Vbuilt-in is the voltage integrated by the relative work function difference between the two electrodes. Series resistance is the voltage caused by the potential drop of series and contact resistance (series resistance = J × Rseries-resistance).
