Solvent Tuning of the Active Layer Morphology of Non‐Fullerene Based Organic Solar Cells

Abstract

Non‐fullerene acceptor (NFA)‐based organic solar cells have made tremendous progress in recent years. For the neat NFA system PBDB‐T:ITIC, the film morphology and crystallinity are tailored by the choice of the solvent used for spin coating the active layers. Three different chlorinated solvents, chlorobenzene (CB), chloroform, and dichlorobenzene, are compared and the obtained active layer morphology is correlated with the optoelectronic properties and the device performance. The small domain sizes in the case of CB are most beneficial for the device performance, whereas the largest number or size of face‐on PBDB‐T crystallites is not causing the highest power conversion efficiencies (PCEs). In addition, when using CB, the number of edge‐on crystallites is highest and the distances between neighboring domains are small. The smoothest blend films are realized with CB, which exhibit correlated roughness with their substrates and no large aggregates have formed in these blend films. Thus, CB offers the best way to balance the aggregation and crystallization kinetics in the active layer and enables the highest PCE values.

High‐Efficiency Binary Organic Solar Cells Enabled by Pseudo‐Bilayer Configuration in Dilute Solution

“…Grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) characterization was performed to analyze the molecular packing and crystalline orientation of BHJ and PBHJ active layer films ( Figure a–c). [ 27 ] The corresponding line‐cut profiles taken along the out‐of‐plane (OOP) and in‐plane (IP) are summarized in Table S2, Supporting Information. The crystalline coherence length (CCL) could be estimated by the equation: CCL = 2 πk /FWHM, in which k is the shape factor typically taken as 0.9 and FWHM is the full width at half maximum diffraction peak.…”

Space‐ and Post‐Flight Characterizations of Perovskite and Organic Solar Cells

“…The 2D GIWAXS data of the PBDB‐T:ITIC organic SCs measured at 0.12° show PBDB‐T (100) Bragg reflexes at ≈0.3 Å −1 for all three samples, the Munich reference, the Sweden reference, and the space SCs (Figure S7, Supporting Information). [ 61 ] This intrinsic polymer crystallinity is present for all the samples in the form of a primarily isotropic ring, apart from the out‐of‐plane direction where the SAXS region overlays. The space sample is in this regard the only sample that shows a weak second‐order peak in out‐of‐plane direction at ≈0.55 Å −1 , which cannot be found for the Munich and Sweden reference samples.…”

“…Apparently, from closer inspection of the inner q-region at around 0.3-0.5, and 1.3-1.7 Å À1 crystalline signal of the polymer bulk-heterojunctions can be found. [61,62] To assess the differences between the Munich, Sweden, and space samples in more detail, out-of-plane and in-plane sector cuts are shown in Figure 8 for PTB7-Th:PCBM and accordingly for PBDB-T:ITIC in Figure S8, Supporting Information.…”

Finely Tuned Molecular Packing Realized by a New Rhodanine-Based Acceptor Enabling Excellent Additive-Free Small- and Large-Area Organic Photovoltaic Devices Approaching 19 and 12.20% Efficiencies

“…As a result, it would be considerably simpler to control the blend film morphology utilizing some of the available active layer materials to achieve the desired performance. Great efforts have been made to tune the morphology of NFA-based OSCs, utilizing suitable coating solvents (chlorobenzene (CB) and chloroform (CF)), , additives (liquid and solid), , and post-treatments (thermal annealing (TA) strategies), , rendering a PCE of more than 18% . On the other hand, the continuously increasing performance of NFA-based OSCs falls short of expectations in terms of concept.…”