The use of non-fullerene acceptors in organic photovoltaic (OPV) devices could lead to enhanced efficiencies due to increased open-circuit voltage (VOC) and improved absorption of solar light. Here we systematically investigate planar heterojunction devices comprising peripherally substituted subphthalocyanines as acceptors and correlate the device performance with the heterojunction energetics. As a result of a balance between VOC and the photocurrent, tuning of the interface energy gap is necessary to optimize the power conversion efficiency in these devices. In addition, we explore the role of the charge transport layers in the device architecture. It is found that non-fullerene acceptors require adjusted buffer layers with aligned electron transport levels to enable efficient charge extraction, while the insertion of an exciton-blocking layer at the anode interface further boosts photocurrent generation. These adjustments result in a planar-heterojunction OPV device with an efficiency of 6.9% and a VOC above 1 V.

Four hexachlorosubphthalocyanines SubPcCl 6 -X bearing different axial substituents (X) have been synthesized for use as novel electron acceptors in solution-processed bulkheterojunction organic solar cells.S ubphthalocyanines are aromatic chromophoric molecules with cone-shaped structure, good solution processability,i ntense optical absorption in the visible spectral region, appropriate electron mobilities,a nd tunable energy levels.S olar cells with subphthalocyanines as the electron acceptor and PTB7-Th as the electron donor exhibit apower conversion efficiency up to 4%and an external quantum efficiency approaching 60 %d ue to significant contributions from both the electron donor and the electron acceptor to the photocurrent, indicating ap romising prospect of non-fullerene acceptors based on subphthalocyanines and structurally related systems.

An optimization of several aspects of planar heterojunction solar cells based on boron subnaphthalocyanine chloride (SubNc) as a donor material is presented. The use of hexachlorinated boron subphthalocyanine chloride (Cl6SubPc) as an alternative acceptor to C60 allows for the simultaneous increase of the short‐circuit current, fill factor, and open‐circuit voltage compared to cells with fullerene acceptors. This is due to the complementary absorption of Cl6SubPc versus SubNc, reduced recombination at the heterointerface, and improved energetic alignment. Furthermore, insertion of a thin diindeno[1,2,3‐cd:1′,2′,3′‐lm]perylene (DIP) layer at the anode results in a very significant 60% increase in photocurrent owing to reduced exciton quenching at the anode. The simultaneous improvement of all three solar cell para­meters results in a power conversion efficiency of 6.4% for a non‐fullerene planar heterojunction cell.

A series of peripherally dicyano-, tricyano-, and tetracyano-substituted subphthalocyanines (SubPcs) have been prepared through microwave-assisted, palladium-mediated cyanation of iodinated precursors. The introduction of π-accepting cyano groups in the macrocycle clearly influences its electronic and redox properties, which are dependent on the number and relative position of these substituents. Additional functionalization of the periphery of SubPcs with electron-donating or -withdrawing groups allows for a further fine-tuning of their features, leading to intensely absorbing, strongly electron-accepting panchromatic dyes with low-lying LUMO energy levels. Flash-photolysis time-resolved microwave conductivity measurements on vapor-deposited films demonstrate that some of these novel SubPc derivatives display remarkable intrinsic charge-carrier mobilities that are comparable to or larger than those of other known well-performing acceptor SubPcs; thus confirming their potential as n-type organic semiconductors for application in the fabrication of photovoltaic devices.

Unsymmetrical subphthalocyanine fused dimers have been prepared, resulting in unprecedented push–pull π-extended curved aromatic macrocycles.

A tweezer-like subphthalocyanine-based ensemble has been developed for the selective recognition of fullerenes. The physicochemical properties of both the photoactive receptor and its inclusion complexes with fullerenes have been investigated.

Four hexachlorosubphthalocyanines SubPcCl6-X bearing different axial substituents (X) have been synthesized for use as novel electron acceptors in solution processed bulk-heterojunction organic solar cells. Subphthalocyanines are aromatic chromophore molecules with cone-shaped structure, good solution processability, intense optical absorption in the visible spectral region, appropriate electron mobilities, and tunable energy levels. Solar cells with subphthalocyanines as the electron acceptors and PTB7-Th as the electron donor exhibit a power conversion efficiency up to 4% and an external quantum efficiency approaching 60% due to significant contributions from both the electron donor and acceptor to the photocurrent, indicating a promising prospect of non-fullerene acceptors based on subphthalocyanines and structurally related systems.Solution processed bulk-heterojunction (BHJ) organic solar cells (OSCs) are a promising renewable energy technology towards future efficient, large-area, flexible photovoltaic modules. [1] The main component of an OSC is its BHJ active layer, consisting of an electron donor and an electron acceptor phase separated into a bi-continuous interpenetrating network morphology.[2] Power conversion efficiencies (PCEs) exceeding 11% have been achieved recently.[3] While numerous electron donors, including semiconducting polymers and small molecules, have been assessed, [4] electron acceptor components are still dominated by fullerene derivatives because of their high electron mobility, ideal frontier orbital energy levels, and isotropic charge transport properties.[5] However, fullerene derivatives have intrinsic shortcomings, such as high cost of synthesis, low absorption coefficients in the visible spectral region, limited variability in energy level, and morphological instability in the blended films.[6] The development of new electron acceptors which overcome the drawbacks associated with fullerene-based acceptors is thus vital for further advancing OSCs. [7] Encouragingly, several studies have reported BHJ solar cells with PCEs >8% based on non-fullerene acceptors.[8]Subphthalocyanines (SubPcs) are aromatic chromophore molecules including a boron atom at their inner cavity, with intense optical absorption in the 460−580 nm spectral region, [9] and relatively high electron mobilities.[10] Traditionally, they have been used as electron donors in vacuum deposited planar heterojunction solar cells.[9a] However, the electronic properties of SubPcs can be easily adjusted by introducing axial and/or peripheral substituents.[9a] Hence, by rational molecular design, i.e.introducing peripheral electron withdrawing groups, SubPcs have been transformed into electron acceptor molecules. [11] In this context, non-fullerene, vacuum evaporated solar cells containing SubPc molecules achieved a PCE of 8.4%.[12] The cone-shaped structure of SubPcs prevents excessive aggregation in solution and solid state, providing good solution processability even without the assistance of electrically i...

Invited for the cover of this issue is the groups of M. V. Martínez‐Díaz and T. Torres at the Universidad Autónoma de Madrid, and S. Seki at the Kyoto University. The image depicts a subphthalocyanines vortex with strong electron‐attraction ability. Read the full text of the article at https://doi.org/10.1002/chem.201801190.