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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]

Volatile solid additives have attracted increasing attention in optimizing the morphology and improving the performance of currently dominated non‐fullerene acceptor‐based organic solar cells (OSCs). However, the underlying principles governing the rational design of volatile solid additives remain elusive. Herein, a series of efficient volatile solid additives are successfully developed by the crossbreeding effect of chalcogenation and iodination for optimizing the morphology and improving the photovoltaic performances of OSCs. Five benzene derivatives of 1,4‐dimethoxybenzene (DOB), 1‐iodo‐4‐methoxybenzene (OIB), 1‐iodo‐4‐methylthiobenzene (SIB), 1,4‐dimethylthiobenzene (DSB) and 1,4‐diiodobenzene (DIB) are systematically studied, where the widely used DIB is used as the reference. The effect of chalcogenation and iodination on the overall property is comprehensively investigated, which indicates that the versatile functional groups provided various types of noncovalent interactions with the host materials for modulating the morphology. Among them, SIB with the combination of sulphuration and iodination enabled more appropriate interactions with the host blend, giving rise to a highly ordered molecular packing and more favorable morphology. As a result, the binary OSCs based on PM6:L8‐BO and PBTz‐F:L8‐BO as well as the ternary OSCs based on PBTz‐F:PM6:L8‐BO achieved impressive high PCEs of 18.87%, 18.81% and 19.68%, respectively, which are among the highest values for OSCs. [ABSTRACT FROM AUTHOR]

Employing volatile solid additives have emerged as a promising method to optimize the morphology and improve the performance of organic solar cells (OSCs). However, principles governing the efficient design of solid additives remain elusive. Herein, the programmed fluorination and/or bromination on benzene core to develop efficient additives for OSCs is reported. The programmed fluorination and/or bromination endow the five halogen benzene derivatives, 1,3,5‐trifluorobenzene, hexafluorobenzene, 1,3,5‐tribromo‐2,4,6‐trifluorobenzene (TFTB), 1,3,5‐tribromobenzene, and hexabromobenzene, with different melting and boiling points, volatility, as well as interactions with the host blend. Studies indicate that the additives with extremely high and low volatility are almost powerless and even detrimental to the morphology evolution. Among them, the combination of fluorine and bromine atoms on TFTB not only enables the more appropriate m.p./b.p. and volatility, but also exerts stronger molecular interactions with the host blend, giving rise to higher ordered molecular packing and more favorable morphology. Importantly, TFTB exhibits good universality to optimize the performances of OSCs with high power conversion efficiencies (PCEs; over 18%) in a group of binary blend systems, and an impressive PCE of 19.43% in the ternary PBTz‐F:PM6:L8‐BO system. [ABSTRACT FROM AUTHOR]

Despite remarkable breakthrough made by virtue of "polymerized small‐molecule acceptor (PSMA)" strategy recently, the limited selection pool of high‐performance polymer acceptors and long‐standing challenge in morphology control impede their further developments. Herein, three PSMAs of PYDT‐2F, PYDT‐3F, and PYDT‐4F are developed by introducing different fluorine atoms on the end groups and/or bithiophene spacers to fine‐tune their optoelectronic properties for high‐performance PSMAs. The PSMAs exhibit narrow bandgap and energy levels that match well with PM6 donor. The fluorination promotes the crystallization of the polymer chain for enhanced electron mobility, which is further improved by following n‐doping with benzyl viologen additive. Moreover, the miscibility is also improved by introducing more fluorine atoms, which promotes the intermixing with PM6 donor. Among them, PYDT‐3F exhibits well‐balanced high crystallinity and miscibility with PM6 donor; thus, the layer‐by‐layer processed PM6/PYDT‐3F film obtains an optimal nanofibril morphology with submicron length and ≈23 nm width of fibrils, facilitating the charge separation and transport. The resulting PM6/PYDT‐3F devices realizes a record high power conversion efficiency (PCE) of 17.41% and fill factor of 77.01%, higher than the PM6/PYDT‐2F (PCE = 16.25%) and PM6/PYDT‐4F (PCE = 16.77%) devices. [ABSTRACT FROM AUTHOR]

A robust hole transporting layer (HTL), using the cost‐effective Cobalt(II) acetate tetrahydrate (Co(OAc)2⋅4 H2O) as the precursor, was simply processed from its aqueous solution followed by thermal annealing (TA) and UV‐ozone (UVO) treatments. The TA treatment induced the loss of crystal water followed by oxidization of Co(OAc)2⋅4 H2O precursor, which increased the work function. However, TA treatment differently realize a high work function and ideal morphology for charge extraction. The resulting problems could be circumvented easily by additional UVO treatment, which also enhanced the conductivity and lowered the resistance for charge transport. The optimal condition was found to be a low temperature TA (150 °C) followed by simple UVO, where the crystal water in Co(OAc)2⋅4 H2O was removed fully and the HTL surface was anchored by substantial hydroxy groups. Using PM6 as the polymer donor and L8‐BO as the electron acceptor, a record high PCE of 18.77 % of the binary blend OSCs was achieved, higher than the common PEDOT:PSS‐based solar cell devices (18.02 %). [ABSTRACT FROM AUTHOR]

A robust hole transporting layer (HTL), using the cost‐effective Cobalt(II) acetate tetrahydrate (Co(OAc)2⋅4 H2O) as the precursor, was simply processed from its aqueous solution followed by thermal annealing (TA) and UV‐ozone (UVO) treatments. The TA treatment induced the loss of crystal water followed by oxidization of Co(OAc)2⋅4 H2O precursor, which increased the work function. However, TA treatment differently realize a high work function and ideal morphology for charge extraction. The resulting problems could be circumvented easily by additional UVO treatment, which also enhanced the conductivity and lowered the resistance for charge transport. The optimal condition was found to be a low temperature TA (150 °C) followed by simple UVO, where the crystal water in Co(OAc)2⋅4 H2O was removed fully and the HTL surface was anchored by substantial hydroxy groups. Using PM6 as the polymer donor and L8‐BO as the electron acceptor, a record high PCE of 18.77 % of the binary blend OSCs was achieved, higher than the common PEDOT:PSS‐based solar cell devices (18.02 %). [ABSTRACT FROM AUTHOR]

BTP-based polymer accepters with low-lying HOMO level and reduced synthesis complexity were developed for all polymer solar cells. Top PCEs of 14.32% and 16.04% were achieved in binary and ternary blends using such BTP-based polymer acceptors, even featuring a very low FOM of 3.65. [Display omitted] • BTP based polymer acceptors were designed and synthesized. • The BTP-based polymers show high performances with the lowest cost-efficiency. • The top PCE of 16.04% was obtained in ternary blend All-PSCs. All-polymer solar cells (All-PSCs) attracted increasing attention due to the outstanding thermal stability and mechanical properties. The current prevailing polymer acceptors for most efficient All-PSCs are polymerized high-performance small molecule acceptor of Y6, i.e. the dithienothiopheno[3,2-b]-pyrrolobenzothiadiazole (BTTP) based polymers. However, the BTTP-based polymers often show relatively shallow highest occupied molecular orbital (HOMO) energy level and high figure of merit (FOM), which limit the rational selection of paring donor polymers. Herein, we presented two low-cost polymer acceptors, namely as BTP-T2F and BTP-2T2F, based on lowly fused dithienopyrrolo[3,2b]benzothiadiazole (BTP, removing two thiophene cycles from BTTP). The BTP-based polymers exhibited deeper HOMO levels around −5.90 eV, which could match variable donor polymers with low-lying HOMO levels, such as low-cost PTQ10. Additionally, the synthesis was significantly simplified compared to BTTP-based polymers. A power conversion efficiency (PCE) of 14.32% was achieved in binary blend device containing PTQ10:BTP-2T2F. By adding a miscibility-enhancing PBDTCl-TPD as a third component, the top PCE of 16.04% was obtained in ternary blend All-PSCs. Combining the high device performance and low estimated cost, extraordinary cost-efficiency balance was realized within these BTP-based polymer acceptors. [ABSTRACT FROM AUTHOR]