Porphyrins-based Materials as Efficient Donor in Organic Solar Cells

Abstract

Twenty years after the discovery of bulk heterojunction solar cells (BHJSCs), porphyrins were underrepresented in the field of organic solar cells (OCSs)1 despite their high epsilon of 300 000 M-1cm-1 and their electron rich aromatic core, which make them a good electron donors. In 2012, a power conversion efficiency (PCE) of 8.08% for a BHJSC built with a small molecule containing a porphyrin core was reported.2 Then in 2017, a PCE of 6.44 % was reported for BHJSC constructed with a polymer containing a porphyrin inside the conjugated chain.3 These advances brought porphyrins at the center of attention in the field of OSCs. In 2019, using a planar non-fullerene acceptor and a porphyrin based-polymer, a 9.16% PCE was reported; a record for this type of dye.4 Both a high Voc of 1.01 V and a low Eloss of 0.45 eV, two BHJSC’s characteristics, make the porphyrin dyes competing with the most efficient donors of the field. Mechanistically speaking, like all donors porphyrin-based donors form interfacial charge transfer (CT) species with the acceptors where upon excitation, a charge separated (CS) state is produced efficiently. However, detailed investigations of the CT signature and photophysical traits of these species simply do exit due to the bulk nature of the materials. We designed a supramolecular porphyrin-graphene nanoribbon (GNR) model taking advantage of π-stacking effects between GNRs and anchoring pyrene groups. Upon selective excitation of the GNRs, the GNRs form excitons for which 95% are involved in an energy transfer with the π-stacked porphyrin-GNR CT species very efficiently (35%in 759 fs; 65% < 135 fs), then an electron transfer (charge separation) occurs from these excited CT species to the GNRs in the ps time scale. 1. Bucher, L.; Desbois, N.; Harvey, P.; Sharma, G.; Gros. C.; Porphyrins and BODIPY as Building Blocks for Efficient Donor Materials in Bulk Heterojunction Solar Cells. Solar RRL 2017, 1, 1700127.2. Huang, Y.; Li, L.; Peng, X.; Peng, J.; Cao, Y.; Solution processed small molecule bulk heterojunction organic photovoltaics based on a conjugated donor–acceptor porphyrin. J. Mater. Chem. 2012, 22, 21841-21844.3. Bucher, L.; Tanguy, L.; Fortin, D.; Desbois, N.; Harvey, P.; Sharma, G.; Gros, C.; A Very Low Band Gap Diketopyrrolopyrrole–Porphyrin Conjugated Polymer. Chempluschem 2017, 82, 625-630.4. Tanguy, L.; Malhotra, P.; Singh, S.; Brisard, G.; Sharma, G.; Harvey, P.; A 9.16% Power Conversion Efficiency Organic Solar Cell with a Porphyrin Conjugated Polymer Using a Nonfullerene Acceptor. ACS Appl. Mater. Interfaces 2019, 11, 31, 28078-28087. Figure 1