High‐Performance Large‐Area Organic Solar Cells Enabled by Sequential Bilayer Processing via Nonhalogenated Solvents

Abstract

power conversion efficiency (PCE) of BHJ devices strongly depends on phase separation of the donor and acceptor. However, the formation of BHJ morphology is an extremely complicated process and the formed morphology is also a highly delicate balance involving many parameters such as domain size, purity, miscibility, etc. To achieve high-performance devices, much effort has been devoted to delicately control the morphology of the active layer (such as the blend ratio between the donor and acceptor, [9][10][11] the type of solvent, [12][13][14] the type and amount of processing additive, [15][16][17] and thermal and solvent annealing [18][19][20] ) to obtain optimal interpenetrated nanoscale phase separation. What is worse, the morphology control becomes much more challenging when the device area is scaled up, for example, the morphology of printed film may vary drastically when the processing condition changes. For this reason, there are typically large performance drops when OPV devices are scaled up to large area or processed using printing techniques. [21,22] Moreover, green solvent is a prerequisite for the commercialization of OSCs. However, for the BHJ structure, the solubility and miscibility of both the donor and acceptor must be taken into consideration together, which limits the selection of a processing solvent. Most OSCs were processed with toxic halogen solvents, and only a few high-performances donor/acceptor combinations were reported in the literature using low toxicity/nontoxic solvents.In contrast, sequential deposition of the donor and acceptor materials followed by post thermal annealing can lead to a similar BHJ morphology and reasonably efficient OSC devices. The interpenetration between donor and acceptor during the solution processing ensures the D/A interfaces for separation of the charges. [23][24][25] The bilayer structure should be more favorable for charge transport as the separated charges can easily transport to each electrode through the D or A layer with low possibility of recombination. [26][27][28] In addition, as both donor and acceptor layers can be processed and optimized independently, this bilayer structure should show less dependence on the D/A ratio, solvent, additive, etc., when compared with the BHJ structure. These properties make the bilayer structure very attractive for achieving high-performance OSCs and While the performance of laboratory-scale organic solar cells (OSCs) continues to grow over 13%, the development of high-efficiency large area OSCs still lags. One big challenge is that the formation of bulk heterojunction morphology is an extremely complicated process and the formed morphology is also a highly delicate balance involving many parameters such as domain size, purity, miscibility, etc. The morphology control becomes much more challenging when the device area is scaled up. In this work, a highly efficient (12.9%) nonfullerene organic solar cell processed using a sequential bilayer deposition method from nonhalogenated solvents, is reported. Using this bi...

Achieving Thickness‐Insensitive Morphology of the Photoactive Layer for Printable Organic Photovoltaic Cells via Side Chain Engineering in Nonfullerene Acceptors

“…2019, 9,1900044 an almost comparable PCE with those of the devices fabricated by the spin coating method. [54,55] In addition, as expected results via the spin coated devices, the printed photoactive layer exhibits a homogeneous and smooth surface morphology with a small RMS roughness of 1.99 nm even at the thickness of ≈300 nm ( Figure S11 (see Figures 8c and 3a,c). Based on this study, we found that the morphology of the photoactive layer is strongly dependent on the inherent properties of m-ITIC-Rs.…”

High‐Performance Pseudoplanar Heterojunction Ternary Organic Solar Cells with Nonfullerene Alloyed Acceptor

“…However, such a method is unable to separate the donors and the acceptors, the vertical phase separation of the active layers are still not well regulated. There are also related literature reporting the use of orthogonal solvents or simultaneously citing a third solvent to increase the donor and the acceptor contact areas, and achieve higher efficiency whereas the choice of orthogonal solvents and device preparation process are more complicated 31–35. By summarizing the advantages and disadvantages of the above literature, we can find that when donor and acceptor materials were dissolved using nonorthogonal solvents, the processing of the films were well completed which can also regulate vertical phase separation well 36.…”

“…However, the citing a third solvent to increase the donor and the acceptor contact areas, and achieve higher efficiency whereas the choice of orthogonal solvents and device preparation process are more complicated. [31][32][33][34][35] By summarizing the advantages and disadvantages of the above literature, we can find that when donor and acceptor materials were dissolved using nonorthogonal solvents, the processing of the films were well completed which can also regulate vertical phase separation well. [36] Therefore, it is feasible to construct a bilayer active layer by sequential spin-coating.…”

A New Wide Bandgap Donor Polymer for Efficient Nonfullerene Organic Solar Cells with a Large Open‐Circuit Voltage

“…Thus, although it is highly challenging, achieving highly efficient NFOSCs by using environmental friendly solvent would have profound impacts in the research field. [6,[40][41][42][43][44] Herein, we designed and synthesized a novel building block methyl 2,5dibromo4fluorothiophene3carboxylate (FET), a monothiophene functionalized with both fluorine (F) atom and ester (E) group. FET was copolymerized with BDT to afford a new polymer donor P1 ( Figure 1).…”