photon management. SF enables multiple excitons to be generated after the absorption of just a single photon. [1-9] By integrating SF materials into solar-cell architectures, it is feasible to increase the overall efficiency of solar cells by pushing the Shockley-Queisser limit from 32% to approximately 45%. Several requirements must, however, be met to allow for efficient SF well beyond 100%. [10,11] Thermodynamically, the energy level of the singlet excited state (S 1) must be equal to or higher than twice that of the triplet excited state (T 1); (S 1) ≥ 2(T 1). [2,3,12] In addition, the energy levels of higher-lying triplet excited states (T 2) should exceed twice the energy of the lowest-lying triplet excited state; (T 2) ≥ 2(T 1). [2,3,12] The latter avoids (T 2) population as a product of triplet-triplet annihilation up-conversion (TTA-UC). [2,3,12] Sufficient electronic interaction between two or more chromophores is essential, and is usually realized for monomers by overlaps in the crystal packing or high concentrations in the solid state or solution, respectively. [12-16] Dimers, in which different spacers are employed to link the chromophores, rather than monomers, represent yet another strategy to adjust and fine-tune, for Three diketopyrrolopyrrole (DPP) dimers, linked via different dithienylphenylene spacers, ortho-DPP (o-DPP), meta-DPP (m-DPP), and para-DPP (p-DPP), are synthesized, characterized, and probed in light of intramolecular singlet fission (i-SF). Importantly, the corresponding DPP reference (DPP-Ref) singlet and triplet excited state energies of 2.22 and 1.04 eV, respectively, suggest that i-SF is thermodynamically feasible. The investigations focus on the impact of the relative positioning of the DPPs, and give compelling evidence that solvent polarity and/or spatial overlap govern i-SF dynamics and efficiencies. Polar solvents make the involvement of an intermediate charge transfer (CT) state possible, followed by the population of 1 (T 1 T 1) and subsequently (T 1 + T 1), while spatial overlap drives the mutual interactions between the DPPs. In o-DPP, the correct balance between polar solvents and spatial overlap leads to the highest triplet quantum yield (TQY) of 40%. Notable is the superimposition of CT and triplet excited states, preventing an accurate TQY determination. For m-DPP, poorer spatial overlap correlates with weaker CT character and manifests in a TQY of 11%. Strong CT character acts as a trap and prevents i-SF, as found with p-DPP. The DPP separation is decisive, enabling a symmetry-breaking charge-separated state rather than CT formation, shutting down the formation 1 (T 1 T 1).

In this revision we have highlighted the most relevant works from the last few years involving diketopyrrolopyrroles (DPPs) as single molecules in organic photovoltaic devices. We have given a tour...

Four ZnPc‐dimers with 2,5‐thienyl (ZnPc−th−ZnPc 1), 2,7‐fluorenyl (ZnPc−flu−ZnPc 2), 3,6‐bisthienylldiketopyrrolopyrrole (ZnPc−DPP−ZnPc 3) and 1,4‐phenyl (ZnPc−p−ZnPc 4) bridges have been studied as dopant‐free hole transporting materials (HTMs) in perovskite solar cells (PSCs). The synthesis and characterization of ZnPc−th−ZnPc 1 and ZnPc−flu−ZnPc 2 dimers are reported for the first time. Steady state and time resolved photoluminescence demonstrate the good hole‐extraction capability of these materials. The best efficiencies obtained for dimers 1, 2, 3 and 4 are 15.5 %, 15.6 %, 16.8 % and 15.7 %, respectively, without the addition of dopants. Besides, these derivatives demonstrated better stability both in dark storage conditions with a relative humidity <20 % for 500 h and at 50 °C with a relative humidity >60 % for 160 h when compared to doped spiro−OMeTAD. The push‐pull nature of dimer ZnPc−DPP−ZnPc 3 has led to the highest efficiency among the ZnPc derivatives under study demonstrating that donor‐acceptor‐donor systems can be good alternatives to commonly used materials due their energy levels, low cost and the final morphology of the hole transporting layer.

We developed triple bonded π-conjugated zinc-phthalocyanine dimers (ZnPc-t-DPP-t-ZnPc 1, ZnPc-t-t-ZnPc 2, ZnPc-t-Spiro-t-ZnPc 3) through molecular engineering, these dimers were then employed as hole selective layers for perovskite solar cell.

Dedicated to Prof. Dr. Nazario Martín on the occasion of his 65th birthdayFour star-shaped electron acceptors (C 1 -OPh, C 3 -OPh, C 1 -Cl and C 3 -Cl) based on a subphthalocyanine core bearing three diketopyrrolopyrrole wings linked by an acetylene bridge have been synthesized. These derivatives feature two different axial substituents (i. e., 4-tert-butylphenoxy (OPh) or chlorine (Cl)) and for each of them, both the C 1 and the C 3 regioisomers have been investigated. The four compounds exhibit a broad absorption band in the 450-700 nm region, with bandgap values near to 2 eV. These materials were applied in the active layer of inverted bulk-heterojunction polymer solar cells in combination with the donor polymer PBDB-T. Derivatives bearing the OPh axial group showed the best performances, with C 1 -OPh being the most promising with a PCE of 3.27 % and a V oc as high as 1.17 V. Despite presenting the widest absorption range, the photovoltaic results obtained with C 1 -Cl turned out to be the lowest (PCE = 1.01 %).