Strategies to improve cyanine dye multi layer organic solar cells

Abstract

We report the status and strategies to improve the performance of cyanine dye/C60 bilayer heterojunction solar cells. Cyanines are characterized by convenience of synthesis and tunable light absorption. They have high light extinction coefficients, which offer the possibility to go around the constraints of small exciton diffusion length, and ultrathin films can be applied to fabricate multi layer organic solar cells. We optimized the cell performance by oxidative doping (with O2/water/light, or NOBF4) of the cyanine layer. Doping increased the film conductivity and induced a steep rise in the short‐circuit current and the open‐circuit voltage. The external quantum efficiency approached 80% at maximum, meaning that the full cyanine layer of 30 nm thickness was active in charge generation. We argue that cyanine aggregates may be responsible for efficient charge transport over larger distances to the heterointerface. We also describe simple processes to match the energy to the low‐lying hole‐transporting cyanine level by using a thin organic salt layer or doped polyaniline as anode buffer layer. Thereby, hole injection was facilitated and good‐performing devices (power conversion efficiency η = 3%) with a high fill factor (FF ∼60%) were fabricated. Cyanine dyes are accompanied by mobile counter ions. These ions can diffuse into adjacent layers and build up important space charge that alters the energy levels at heterojunctions. The control of the ionic space charge allows to control the flow of electronic charge carriers and to implement new functionalities unique to organic opto‐electronic devices. Copyright © 2010 John Wiley & Sons, Ltd.

Fluorescent J-aggregates of cyanine dyes: basic research and applications review

“…It can be enhanced in multi-layer constructions, in which fullerenes or carbon nanotubes mediate the electron transfer from strongly absorbing ultrathin films of J-aggregates [243,244]. The operation of photodetectors consisting of cyanine dye J-aggregates and metal oxide thin films can be extended to near-IR range [102].…”

Layer‐by‐Layer Processed Organic Solar Cells

“…[63,[75][76][77][78][79][159][160][161][162][163][164][165][166][167][168][169][170][171][172][173][174][175] For example, polymer/ C 60 (C 70 ) system is mostly used in LL OPVs since C 60 (C 70 ) can only be deposited using vacuum evaporation. With this method, a controlled and sharp interface can be realized.…”

“…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.…”

Photophysical Studies of a New Water Soluble Indocarbocyanine Dye Adsorbed onto Microcrystalline Cellulose and beta-Cyclodextrin

“…In addition to their use as traditional colorants [1,2,3], they have found potential applications in energy conversion [4,5,6], as laser dyes [1,2,7], as fluorescent labeling agents for biological applications [8,9,10] and in electro-optical applications [11,12,13,14,15,16,17]. Moreover, cyanine dyes, which were previously used as spectral sensitizers in photographic emulsions [18], are currently used as photo-initiators in photo-polymerization [19,20] and as potential sensitizers for photodynamic therapy [21,22,23,24,25].…”

“…Although cyanine dyes exhibit high extinction coefficients and efficient absorption over a long range of the optical spectrum [1,2,3,4,5,6], in fluid solution and at room temperature, the number of highly fluorescent dyes is rather small [26]. For sterically non-hindered cyanines in the monomeric form, this results from an efficient radiationless deactivation of the excited states by trans-cis isomerisation as the main decay route of the S 1 state [1,2,26].…”