Abstract
The high efficiency all-small-molecule organic solar cells (OSCs) normally require optimized morphology in their bulk heterojunction active layers. Herein, a small-molecule donor is designed and synthesized, and single-crystal structural analyses reveal its explicit molecular planarity and compact intermolecular packing. A promising narrow bandgap small-molecule with absorption edge of more than 930 nm along with our home-designed small molecule is selected as electron acceptors. To the best of our knowledge, the binary all-small-molecule OSCs achieve the highest efficiency of 14.34% by optimizing their hierarchical morphologies, in which the donor or acceptor rich domains with size up to ca. 70 nm, and the donor crystals of tens of nanometers, together with the donor-acceptor blending, are proved coexisting in the hierarchical large domain. All-small-molecule photovoltaic system shows its promising for high performance OSCs, and our study is likely to lead to insights in relations between bulk heterojunction structure and photovoltaic performance.
Highlights
The high efficiency all-small-molecule organic solar cells (OSCs) normally require optimized morphology in their bulk heterojunction active layers
For ZR1:IDIC-4Cl films annealed at 120 °C, the domain size of the coexisting large and small phase area turned out to be 147.4 nm and 6.2 nm, respectively (Fig. 3h). These results suggest the formation of a hierarchical morphology within the blend i.e., a smaller donor phase, having a size very close to the exciton diffusion length of ca. 10 nm which accounts for the efficient charge separation, along with a larger donor phase that is responsible for the efficient charge transport within the system
We report the synthesis of a DTBDT-based small-molecule donor, ZR1, and fabricated small-molecule organic solar cells (SM-OSCs) by individually blending it with Y6 and IDIC-4Cl as acceptors
Summary
The high efficiency all-small-molecule organic solar cells (OSCs) normally require optimized morphology in their bulk heterojunction active layers. To the best of our knowledge, the binary all-small-molecule OSCs achieve the highest efficiency of 14.34% by optimizing their hierarchical morphologies, in which the donor or acceptor rich domains with size up to ca. Enhanced crystallization, as well as their tendency to obtain high phase purity and tune crystal orientations enables fabrication of OSCs with high charge mobility and low energy losses (Eloss = Eg − qVOC)[12,14,15] Despite all their advantages, the all-small-molecule organic solar cells (SM-OSCs) still have not shown the same level of device performance as the PSCs. The biggest challenge is to control the interpenetrating networks in SM-OSCs, since the inefficient charge transport pathways would lead to excessive exciton recombination, decreased charge carrier mobility and unbalanced charge-transport ability[16,17,18]. The ZR1:IDIC-4Cl blend films exhibited a highest PCE of 9.64%, which is limited by the relatively higher Eloss and wider bandgap of IDIC-4Cl as compared to Y6
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