Efficient Squaraine-Based Solution Processable Bulk-Heterojunction Solar Cells

Abstract

We report the fabrication of organic bulk-heterojunction solar cells based, for the first time, on squaraine/PCBM blends. The most efficient device, solution-processed in air, exhibits J(sc) = 5.70 mA/cm(2), V(oc) = 0.62 V, fill-factor = 0.35, and power conversion efficiency = 1.24%, one of the highest to date for a small molecule solution-processed bulk-heterojunction cell.

Hole Transport in Diketopyrrolopyrrole (DPP) Small Molecules: A Joint Theoretical and Experimental Study

“…42 However, the mobility has been found to be independent of carrier density in the range 10 14 − 10 16 cm −3 for polymers, 42 which is in the similar range of carrier density for DPP(TBFu) 2 . Thus for simplicity, we assume the hole mobility of DPP(TBFu) 2 to have an equally weak density dependence. Equations 1−3 are solved numerically following the method of van Mensfoort and Coehoorn.…”

“…In order to examine the hole transport in DPP(TBFu) 2 , single carrier diodes with the sandwich structure ITO/PEDOT−PSS/ DPP(TBFu) 2 /Au were fabricated in inert gas environment as follows: 50 nm of poly(3,4-ethylenedioxythiophene)−poly-(styrenesulfonate) (PEDOT−PSS) hole injection layer was spin-coated atop patterned indium−tin oxide (ITO) substrates that were precleaned with sonication in soapy water, acetone, and 2-propanol sequentially. The PEDOT−PSS layer is intended to enhance the wettability and smoothness by offering a work function of 5.1 eV to form an ohmic contact with the HOMO of DPP(TBFu) 2 (5.3 eV, as confirmed by ultraviolet photoemission spectroscopy).…”

“…Until now the morphological behavior in the blend and unbalanced charge transport of the donor and acceptor materials have been the major concerns in smallmolecule OPVs. 5−7 In this paper, we report on a joint theoretical and experimental study of hole transport in disordered small molecules 3,6-bis[5-(benzofuran-2-yl)thiophen-2-yl]-2,5-bis(2-ethylhexyl)pyrrolo [3,4-c]pyrrole-1,4-dione [DPP(TBFu) 2 ], whose molecular structure is shown in Figure 1a. A recent advance in small-molecule OPV has been reported in which DPP(TBFu) 2 had been used as a donor material in bulk heterojunction (BHJ) OPV, resulting in a PCE of as much as 4.4%.…”

“…5−7 In this paper, we report on a joint theoretical and experimental study of hole transport in disordered small molecules 3,6-bis[5-(benzofuran-2-yl)thiophen-2-yl]-2,5-bis(2-ethylhexyl)pyrrolo [3,4-c]pyrrole-1,4-dione [DPP(TBFu) 2 ], whose molecular structure is shown in Figure 1a. A recent advance in small-molecule OPV has been reported in which DPP(TBFu) 2 had been used as a donor material in bulk heterojunction (BHJ) OPV, resulting in a PCE of as much as 4.4%. 8,9 Our focus here on disordered small molecules is motivated by the fact that most OPVs consist of mixed ordered and disordered domains.…”

Determining the absorption tolerance of single chromophore photodiodes for machine vision

“…In addition, organic chromophores often absorb to a significant extent across all wavelengths shorter than the onset of absorption and, particularly in small molecule absorbers, the absorption of the chromophores has been found to be broader in the solid-state than in solution due to aggregation effects. 8,9 In order to investigate the feasibility of implementing our scheme using real materials, we studied the solution and film spectra of four different chromophore types, namely, tetrathiophene 1, neutral 2 and charged 3 cyanines, and squaraine 4 ͑Fig. 2͒ incorporated into a dendritic architecture ͑see Ref.…”