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A double‐fibril network of the photoactive layer morphology is recognized as an ideal structure facilitating exciton diffusion and charge carrier transport for high‐performance organic solar cells (OSCs). However, in the layer‐by‐layer processed OSCs (LbL‐OSCs), polymer donors and small molecule acceptors (SMAs) are separately deposited, and it is challenging to realize a fibril network of pure SMAs with the absence of tight interchain entanglement as polymers. In this work, crystalline small molecule donors (SMDs), named TDZ‐3TR and SeDZ‐3TR, were designed and introduced into the L8‐BO acceptor solution, forcing the phase separation and molecular fibrilization. SeDZ‐3TR showed higher crystallinity and lower miscibility with L8‐BO acceptor than TDZ‐3TR, enabling more driving force to favor the phase separation and better molecular fibrilization of L8‐BO. On the other hand, two donor polymers of PM6 and D18 with different fibril widths and lengths were put together to optimize the fibril network of the donor layer. The simultaneously optimization of the acceptor and donor layers resulted in a more ideal double‐fibril network of the photoactive layer and an impressive power conversion efficiency (PCE) of 19.38 % in LbL‐OSCs. [ABSTRACT FROM AUTHOR]

The most popular approach to fabricating organic solar cells (OSCs) is solution processing a mixture of donor (D) and acceptor (A) materials into an active layer with a bulk heterojunction (BHJ) nanostructure. Herein, it is demonstrated that the interdigitated heterojunction (IHJ) is a more suitable nanostructure of the active layer for high‐performance OSCs whereas it is a long standing challenge to realize well‐defined IHJ structures. In this study, a facile and versatile sequential solution processing method is developed to produce an IHJ nanostructure with power conversion efficiency reaching 18.74% (18.10% for BHJ the counterpart) by fabricating a donor film with nanopores created by a wax additive, sequentially casting the acceptor on top of infiltrating the nanopores. Compared to the BHJ, the IHJ structure with an interpillar distance within the exciton diffusion length can afford a large bulk D/A interface for efficient exciton dissociation with a minimized charge recombination while free electrons and holes can transport to the respective electrodes through more straightforward pathways, thus enhance performance. Furthermore, the D or A phase in the IHJ device contacts with only one electrode, which can prevent shunting between the anode and cathode and facilitate the industrial mass production of OSCs. [ABSTRACT FROM AUTHOR]

Organic semiconductors consist of a conjugated backbone and flexible sidechains. Compared to the meticulous design of backbones, less attention has been paid to the investigation of sidechains, in particular their spatial orientation. Herein, three non‐fullerene acceptors, anti‐PDFC, syn‐PDFC, and PDFC‐Ph, are applied in all‐small‐molecule organic solar cells (ASM‐OSCs) to reveal the varied effects of sidechains on morphology and device performance. With spatially orthogonal alkyl chains, anti‐PDFC and syn‐PDFC show unique bimodal lamellar packing and moderate crystallinity. When blending with an efficient binary BTR‐Cl/Y6 system, anti‐PDFC as well as syn‐PDFC not only form their own crystal phase but also improve the packing order of BTR‐Cl, consequently enhancing the power conversion efficiency (PCE) of ternary ASM‐OSC to be 14.56%. However, although PDFC‐Ph has an identical backbone with anti‐PDFC, the alternated sidechains make it relatively amorphous, which is prone to damage the original packing of the host donor/acceptor, and thus deteriorating the device performance. When PC71BM is added to optimize the morphology further, the triple‐acceptor device involving anti‐PDFC realizes a PCE of 15.67%, which is among the best efficiencies in ASM‐OSCs. This study demonstrates that a multi‐dimensional sidechain can optimize the morphology of a bulk heterojunction as effective as a conjugated backbone. [ABSTRACT FROM AUTHOR]