Arylamine-Based Squaraine Donors for Use in Organic Solar Cells

Abstract

Squaraine (SQ) dyes are notable for their exceptionally high absorption coefficients extending from the green to the near-infrared. In this work, we utilize the functionalized SQ donor: 2,4-bis [4-(N-phenyl-1-naphthylamino)-2,6-dihydroxyphenyl] squaraine (1-NPSQ) by substitution of isobutylamines in the common "parent SQ" with arylamines to improve stacking and hence exciton and charge transport. The strong electron-withdrawing arylamine group results in a highest occupied molecular orbital energy of 5.3 eV, compared to 5.1 eV for the parent SQ, making 1-NPSQ a suitable donor when used with a C(60) acceptor in an organic photovoltaic cell. Optimized and thermally annealed, nanocrystalline heterojunction 1-NPSQ/C(60)/bathocuproine solar cells with an open circuit voltage of 0.90 ± 0.01 V, fill factor of 0.64 ± 0.01, and short circuit current of 10.0 ± 1.1 mA/cm(2) at 1 sun, AM1.5G illumination (solar spectrally corrected) result in a power conversion efficiency of 5.7 ± 0.6%. Crystallograpnic data suggest that the intermolecular stacking of 1-NPSQ molecules is closer than that of the parent SQ, thereby reducing the device series resistance and increasing its fill factor.

Layer‐by‐Layer Processed Organic Solar Cells

“…Fused acenes [34][35][36][37][38][39][40][41][42][43] and several famous classes of dyes, such as phthalocyanine (Pc), [20, subphthalocyanine (SubPc), [66][67][68][69][70][71] subnaphthalocyanine (SubNc), [72,73] merocyanine (MC), [74] cyanine dyes, [75][76][77][78][79] and squaraine (SQ), [80][81][82][83] are widely used in LL vacuum deposited OPVs (Figure 2, Table 1). In 2001, Forrest and Peumans fabricated bilayer heterojunction OPVs based on CuPc and C 60 with a PCE of 3.6% under 150 mW cm −2 simulated AM1.5G illumination.…”

“…[74] Squaraine (SQ) dyes have also shown tremendous potential for LL processed OPVs because of intense absorption in the red and near-infrared spectral regions, ambient stability and non-toxicity. [80][81][82][83] In 2009, Forrest and co-workers reported a vacuum deposited bilayer OPV based on SQ dye DIB-SQ and C 60 with a PCE of 3.2%. [81] Fused acenes especially pentacene have also been widely studied as donor materials in LL vacuum deposited OPVs due to their high hole mobility, broad absorption and good thermal stability.…”

Benzochalcogenodiazole‐Based Donor–Acceptor–Acceptor Molecular Donors for Organic Solar Cells

“…[20] The structural design of molecular donors for SMOSCs has been dominated by symmetrical scaffolds. [21][22][23][24][25] For example, dicyanovinylene end-capped oligothiophenes are among the best studied of vacuum-processed donor materials, and demonstrate excellent photovoltaic performance with PCEs of up to 6.9 %. [24] In addition, oligothiophene derivatives that contain a benzodithiophene core and 3-ethylrhodanine terminal units also exhibited PCEs as high as 8.12 % in solution-processed SMOSCs.…”

Organic Semiconductor Photovoltaic Materials

“…Squaraine (SQ) dyes have a unique aromatic four-membered ring with resonance-stabilized zwitterionic structures, and are characterized for their high absorption coefficients and broad absorptions which can extend from the green to the NIR region [18,19,[21][22][23][24]. Forrest, Thompson, and coworkers reported a squaraine-based molecule (1j), for structure see Fig.…”

“…The strong electron-withdrawing arylamine group results in a lower HOMO of −5.3 eV, compared to −5.1 eV for the parent SQ (1j), thereby leading to an increased V OC . Heterojunction 1k/C 60 / bathocuproine solar cells shows an improved efficiency of 5.7 % with a V OC of 0.90 V, FF of 0.64, and J SC of 1.1 mA cm −2 [19]. Organic dyes with a D-A-A (donor−acceptor−acceptor) structure have both a smaller bandgap and lower-lying highest occupied molecular orbital (HOMO) level as compared with their analogs.…”