A bacteriochlorin-diketopyrrolopyrrole triad as a donor for solution-processed bulk heterojunction organic solar cells

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2019, Vol.7 (31), p.9655-9664
• Main Authors: Ponsot, Flavien, Bucher, Léo, Desbois, Nicolas, Rousselin, Yoann, Mondal, Pritam, Devillers, Charles H, Romieu, Anthony, Gros, Claude P, Singhal, Rahul, Sharma, Ganesh D
• Format: Article
• Language: English
• Subjects: Absorption spectra; Butyric acid; Chlorophyll; Crystallography; Data analysis; Donors (electronic); Efficiency; Energy conversion efficiency; Energy dissipation; Energy gap; Energy levels; Heterojunctions; Molecular orbitals; NMR; Nuclear magnetic resonance; Optimization; Organic chemistry; Photovoltaic cells; Porphyrins; Solar cells; Solvents; Weight
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c9tc02724f

We have designed an A-π-D-π-A small-molecule triad consisting of a bacteriochlorin (BC) donor central core linked with two diketopyrrolopyrrole (DPP) acceptors via ethynyl bridges ( BC-DPP-1 ). BC-DPP-1 has a narrow optical bandgap of 1.38 eV with highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of −4.93 eV and −3.40 eV, respectively, and it was used as an electron donor along with [6,6]-phenyl-C 71 -butyric acid methyl ester ( PC 71 BM ) as an acceptor for solution-processed small-molecule organic solar cells. After optimizing the weight ratio between BC-DPP-1 and PC 71 BM and pyridine as a solvent additive and subsequent solvent vapor annealing using THF, an organic solar cell based on the optimized BC-DPP-1 : PC 71 BM showed an overall power conversion efficiency of 7.48%. Since BC-DPP-1 shows a weak absorption band in the 650-750 nm wavelength region, we used a second small molecule having strong absorption in this spectral region and prepared the ternary active layer BC-DPP-1  :  SM  :  PC 71 BM , varying the weight ratio between the two donors and keeping the amount of PC 71 BM constant. The ternary active layer BC-DPP-1 (70% w/w): SM (30% w/w): PC 71 BM showed the best photovoltaic performance. After the optimization of the ternary active layer ( i.e. , the solvent additive and subsequent solvent vapor additive), the organic solar cell showed overall power conversion efficiency of 9.88%. The improved power conversion efficiency resulted from the enhancement of J sc , V oc and FF as compared to the binary counterpart. Since BC is an analog of porphyrins and chlorophylls, these results demonstrate that benefiting from the narrow band gap of BC-DPP-1 ( i.e. , organic solar cells with light harvesting in the NIR region of the solar spectrum) can be a real improvement. Moreover, the low energy loss (0.48 eV) as compared to the binary counterpart (0.58 eV) also confirms the suppressed recombination in the ternary organic solar cells. A bacteriochlorin-diketopyrrolopyrrole triad formally defined as an A-π-D-π-A electronic system is used as an efficient donor for bulk heterojunction solar cells, alone or combined to a diethynylpyrrole-based wide-bandgap small molecule donor.