Substituted derivatives of hydroquinone/benzoquinone were studied as organic redox mediators in the electrolyte for dye-sensitized solar cells (DSSCs). Thus, di-tert-butylhydroquinone (DTHQ), thymohydroquinone (ThymHQ) and phenylhydroquinone (PhHQ), were combined with their oxidized counterparts to form the pairs DTHQ/DTBQ, ThymHQ/ThymBQ, and PhHQ/PhBQ. In general, the characteristic parameters of the DSSCs with the substituted derivatives surpassed those of the DSSC with the unsubstituted hydroquinone/benzoquinone electrolyte. The short-circuit current (J SC) of the devices using DTHQ/DTBQ and ThymHQ/ThymBQ (13.61 mA cm −2 and 12.56 mA cm −2 , respectively) are comparable to the J SC obtained for cobalt(II/III) tris (bipyridine) as a reference electrolyte (14.54 mA cm −2). However, parameters such as open-circuit voltage (V OC) and fill factor (FF) (547 mV and 0.48, respectively) are far from competitive. The best photovoltaic performance was obtained for the pair ThymHQ/ThymBQ using a triphenylamine (TPA)-based organic dye (LEG4) as sensitizer and a hybrid counter electrode with poly(3,4-ethylenedioxythiophene) (PEDOT) and graphene. These experimental conditions give under 1 sun (98%) the highest efficiency (η = 3.19%); low-light intensities of 12.3% and 51.8% suns lead to efficiencies of 3.34% and 3.29%, respectively. Electrochemical impedance spectroscopy (EIS) revealed that the main cause for loss in photocurrent is the low recombination resistance compared to Co(II/III) as reference electrolyte. Based on the EIS analysis, a down-shift of the conduction band of TiO 2 was found for all assembled devices containing the organic redox mediators, which explains the low V OC values for these derivatives.

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Hole-transport materials (HTMs) are key electronic components for the functioning of perovskite solar cells (PSCs) as they extract the photogenerated holes from the perovskite to be transported subsequently to the back electrode while minimizing the loss from electron recombination. Herein, we report the synthesis and characterization of novel germaniumbased compounds with [{HC(CMeNAr) 2 }GeNCS] (2), [{HC-(CMeNAr) 2 }Ge(S)NCS] (3), and [{HC(CMeNAr) 2 }Ge(Se)-NCS] (4) compositions, with Ar = 2,6-iPr 2 C 6 H 3 and the photovoltaic performance of 3 and 4 that is the same as for HTM in PSC. All compounds displayed excellent thermal properties and an appropriate alignment of energy levels for the perovskite with maximum optical absorption in the near-UV region. As revealed by space-charge limited-current (SCLC) measurements, compounds 3 and 4 have competing hole mobilities of about 1.37 × 10 −4 and 4.88 × 10 −4 cm 2 V −1 s −1 , respectively. Upon assessing PSC devices using 3 and 4 with triple-cation perovskite absorber Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 , the power conversion efficiencies (PCEs) were about 13.03 and 9.23%, respectively, both without doping and additives, and were compared with benchmark HTM spiro-OMeTAD (2,2′,7,7′-tetrakis(N,N-di-pmethoxyphenylamine)-9,9′-spirobifluorene). Quantum chemical calculations with DFT showed that the optoelectronic properties are strongly influenced by the combined contributions of the germanium atom, the pseudohalide moiety (NCS − ), and chalcogenides (S 2− or Se 2− ). Fine tuning the electronic properties of germanium is thus a good strategy for the targeted synthesis of potential conducting molecules in PSCs.

The crystal structure of the title compound, [CoLi(C11H21N2O)Cl2(C4H8O)2], has monoclinic symmetry and comprises one heterometallic binuclear complex molecule in the asymmetric unit. The Co2+ cation is bonded to one oxygen and two nitrogen atoms of a β-ketoiminato ligand and to two chlorido ligands, leading to a distorted trigonal-bipyramidal coordination sphere. One of the Cl ligands and the oxygen atom of the β-ketoiminato ligand are bridging to a Li+ cation, which is further bonded to oxygen atoms of two THF molecules. The resulting coordination sphere is distorted tetrahedral. In the crystal, weak intermolecular C—H...Cl hydrogen bonds are identified that link the complex molecules into a three-dimensional network structure.