High‐Efficiency Nonfullerene Organic Solar Cells: Critical Factors that Affect Complex Multi‐Length Scale Morphology and Device Performance

Abstract

Organic solar cells (OSCs) made of donor/acceptor bulk-heterojunction active layers have been of widespread interest in converting sunlight to electricity. Characterizing of the complex morphology at multiple length scales of polymer:nonfullerene small molecular acceptor (SMA) systems remain largely unexplored. Through detailed characterizations (hard/soft X-ray scattering) of the recordefficiency polymer:SMA system with a close analog, we are able to relate quantitative morphological parameters to the device performance parameters and establish fundamental morphologyperformance relationships that explain why additive use and thermal annealing are needed for optimized performance. A linear correlation between the average purity variations at small length scale (~10 nm) and photovoltaic device characteristics across all processing protocols was observed in ~12%-efficiency polymer:SMA systems. In addition, molecular interactions as reflected by the estimated Flory-Huggins interaction parameters are used to provide context of the room temperature morphology results. Comparison with results from annealed devices suggests that the two SMA systems compared show upper and lower critical solution temperature behavior, respectively. The in-depth understanding of the complex multi-length scale non-fullerene OSC morphology may guide the device optimization and new materials development and indicates that thermodynamic properties of materials systems should be studied in more detail to aid in designing optimized protocols efficiently.

Environmentally-friendly solvent processed fullerene-free organic solar cells enabled by screening halogen-free solvent additives

“…2a shows the current density-voltage (J-V) characteristics of the optimal devices fabricated using different solvent systems and the corresponding parameters are listed in Table 1. The device fabricated using neat XY as the processing solvent exhibits an open-circuit voltage (V oc ) of 0.940 V, a short-circuit current density (J sc ) of 16.3 mA cm −2 , a fill factor (FF) of 0.543 and a PCE of 8.32%, which is much lower than those of the devices fabricated by the CB/DIO combination in our recent work [41,54]. When a trace amount (1%, v/v) of DPE or NMP is added as the solvent additive, the J sc is slightly increased, while the FF is in-creased to 0.603 and 0.657, respectively, hence the PCE can be improved to 9.39% and 10.5%, respectively.…”

“…1c) with a conventional configuration of ITO/PEDOT:PSS/PBDB-T:IT-M/ PFN-Br/Al were fabricated, and the PEDOT:PSS and PFNBr were utilized as the p-type and n-type interlayers, respectively [61]. The weight ratio of PBDB-T and IT-M maintains at 1:1 and the thickness of the active layers is kept at around 100 nm by referring our recent studies [41,54]. Fig.…”

“…1), which had demonstrated high photovoltaic performance in devices [41,53,54]. Prior to the device study, the solubility of PBDB-T in different halogen-free solvents, such as XY, anisole and THF, was initially tested.…”

8.0% Efficient All‐Polymer Solar Cells with High Photovoltage of 1.1 V and Internal Quantum Efficiency near Unity

“…[57] So far, R-SoXS technique has been successfully employed to probe the bulk structures and domain compositions in a few polymer:polymer blends. [58][59][60][61][62][63] Figure 5 and Figure S10 (Supporting Information) depict the Lorentz-corrected R-SoXS profiles for the four blend films. Multiple log-normal peaks were explored to fit the circular averaged scattering profiles for all the samples.…”

Optimizing the Organic Solar Cell Manufacturing Process by Means of AFM Measurements and Neural Networks

“…Among such geometrical values, the cell surface dimension and the thickness, particularly the active layer thickness, influences the performances of the solar cell. Such electrical performances can be devised by means of several parameters such as carrier mobility, the donor-acceptor ratio, the materials' concentrations, and the morphology of the blend [5][6][7][8][9][10][11]. Moreover, in solar cells, electron-hole pairs are formed when light is absorbed.…”