Novel porphins for DSCC and BHJ solar cells

Resumen

Summary Introduction The global challenge of sustainable development, clean energy and climate change needs to be pursued by development of energy technologies. Moreover the energy sector is responsible of two thirds of the world’s greenhouse-gas (GHG) emissions ; therefore the world needs to change the inefficient energy system based on fossil fuels to renewable sources as sunlight, wind, rain, waves, tides, biomass and geothermal heat. Besides solar energy is available throughout the world as radiant light or heat from the sun, using technology such as photovoltaics devices. New generation of photovoltaics can provide an alternative and complementary approach for the exploitation of solar energy; offers low manufacture cost, they are flexible, light, and more environmental friendly; the most promising for their remarkable progress are: organic solar cells, hybrid dye sensitized solar cells, and perovskite solar cells. Nevertheless, in this thesis the first two types of cells will be widely described focusing on devices comprising porphyrins, these molecules have been explored due to their robustness, thermal stability, rich metal coordination chemistry, strong aromaticity, optical, electronic and magnetic properties. Content In the first chapter twelve novel small molecule porphyrins, with configuration A--D--A, were synthesized and characterized to be applied in solution processed bulk heterojunction solar cells (BHJSC). Also zinc porphyrin core (D) and  conjugated linker were separated by an ethynyl group, to improve the planarity and enhance the  conjugation of the system. Moreover each molecule comprise two strong  electron withdrawing moieties (A) to control the absorption spectrum in the near infrared region, by a conjugation with electron rich aromatic units. In order to study, all molecules were synthesized and properly characterized, photophysical and electrochemical properties were measured, and theoretical HOMO-LUMO orbitals and optimized geometries were calculated. Additionally, to complete these studies, devices performance was evaluated and the best PCE (4.24%) was achieved with PC71BM:SA4 (4:1 w/w) (comprising a mesityl zinc porphyrin core, (E)‐1,2‐bis(3,4‐dihexylthiophen-2-yl)ethylne as  conjugated linker and 3-ethylrhodanine as acceptor), with a high short circuit current (JSC) of 13.2 mAcm-2. In the second chapter six novel dyes bearing triphenylamine donor groups were synthesized and characterized. The absorption and electrochemical properties were investigated to determine the electronic features of these compounds. Moreover these molecules were employed as sensitizer for Dye Sensitized Solar Cells (DSSCs), and their efficiencies were measured in nanocrystalline TiO2. The best PCE (6%) was achieved for SA12 employing two thiophene rings connected by a double bond as spacers between the conjugated porphyrin core and the anchoring cyanoacrylate group. Novel designs of porphyrin and improvements in photovoltaic devices can be achieved. Therefore, there is still much work to be done to improve solar cells. Moreover, in the last years the research on this thematic is allowing to develop best photovoltaics. Conclusions I. Twelve new small molecules based on porphyrin with structure A--D--A were designed, synthesized and fully characterized and the performance of all new porphyrin based systems in BHJSC was evaluated. II. Mesityl porphyrin with (E)‐1,2‐bis(3,4‐dihexylthiophen-2-yl)ethylene as bridge and rhodanine as acceptor (SA4), showed a higher JSC (13 mA/cm-1), allowing a higher PCE (4.24%) in comparison to the other optimized devices. III. Porphyrins with 3,4-dihexylthiophene as bridge showed a higher VOC, (0.86 V for SA1 and 0.87 for SA3) than the other optimized porphyrin based devices (0.82 V for SA2, 0.80 for SA4). IV. Porphyrins with rhodanine moiety as acceptor reached higher JSC than porphyrins with dicyanovynil as terminal end, affording a better PCE. V. Porphyrins with (E)‐1,2‐bis(3,4‐dihexylthiophen-2-yl)ethylene as bridge showed higher JSC than porphyrins with other bridges, leading to higher PCE. VI. FFs of all BHJSCs devices are low (30%) and need to be optimized to enhance the efficiency. VII. Six new dyes based on porphyrin with structure D--A were designed, synthesized and properly characterized by spectroscopic techniques. The performance of all new porphyrin based systems in DSSCs devices was evaluated. VIII. Devices with triphenylamineporphyrin, 3,4-dihexylthiophene as bridge and cyanoacrylic acid as anchoring group, SA15, exhibited 0.68 VOC and 12.30 mA cm-2 JSC achieving the higher PCE (6%), in comparison to the other devices. IX. Triphenylamineporphyrin devices with carboxylic acid as anchoring group achieved better JSC (10.09 mA cm-2) with benzene as bridge, SA13, than devices with 3,4-dihexylthiophene as bridge, SA15, (5.61 mA cm-2) and porphyrins with 4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophene as bridge SA18 (2.88 mA cm-2). X. Triphenylamineporphyrin devices with cianoacrylic acid or carboxylic acid as anchoring group and 3,4-dihexylthiophene as bridge, showed a higher VOC (0.68 V and 0.64 V, respectively) in comparison to the other devices with values between 0.57 and 0.57 V. XI. FF of all DSSCs prepared devices showed excellent values, between 67 and 72%. References International Energy Agency (IEA), Energy and Climate Change, World Energy Outlook Special Report 2015, http://www.worldenergyoutlook.org/energyclimate/ (accessed Jul 5, 2015). Royal Society of Chemistry (RSC). Campaigning & Outreach, Tackling Global Challenges: Energy. http://www.rsc.org/campaigning-outreach/global-challenges/energy (accessed Jul 5 2015). Spanggard, H.; Krebs, F. C. Sol. Energ. Mat. Sol. Cells. 2004, 83, 125. cMishra A.; Baüerle, P. Angew. Chem. Int. Ed. 2012, 51, 2020. d Lin, Y.; Li, Y.; Zhan, X. Chem. Soc. Rev. 2012, 41, 4245. e aRagoussi, M. E.; Torres, T. Chem. Commun. 2015, 51, 3957. b Brabec, C.; Dyakonov, V.; Scherf U. Organic Photovoltaics: Materials, Device Physics, and Manufacturing Technologies, 2nd. Ed.; Wiley-VCH: Weinheim, 2014 c Lin, Y.; Li, Y.; Zhan, X. Chem. Soc. Rev. 2012, 41, 4245. Arrechea, S.; Molina-Ontoria, A.; Aljarilla, A.; de la Cruz, P.; Langa, F.; Echegoyen, L. Dyes Pigm. 2015, 121, 109. Aljarilla, A.; Clifford, J. N.; Pelleja, L.; Moncho, A.; Arrechea, S.; de la Cruz, P.; Langa, F.; Palomares, E. J. Mat. Chem. A. 2013, 1, 13640. Arrechea, S.; Clifford, J. N.; Pelleja, L.; Aljarilla, A.; de la Cruz, P.; Palomares, E.; Langa, F. Dyes Pigm. 2016, 126, 147-153