Polymers in photovoltaic devices

Photovoltaic (PV) cells generate electric power when irradiated with sunlight or artificial light. Classical PV cells, based on inorganic semiconducting materials 

Certain organic materials also possess semiconductor properties and can be employed in PV cells, a fact that has recently been attracting growing interest since the advent of novel polymeric materials [22, 60-66]. Table 6.5 lists some typical polymers used in solar cells. 

Criteria commonly used to characterize PV cells comprise Jso the short-circuit current density, Voo the open-circuit voltage 0cc the quantum efficiency for 

MDMO-PPV Poly[2-methoxy-5-(3, 7 -dimethyl-octyloxy)-l,4-phenylene vinylene] 

MEH-PPV Poly[2-methoxy-5-(2 -ethyl-hexyl-oxy)-l,4-p henylene vinylene] 

---

Schubert98 proposed the potential use of several ruthenium containing polymers in photovoltaic devices. A ruthenium containing poly(ethylene glycol) derivative 34 was synthesized by the functionalization of 4-(3-aminopropyl)-4-methyl-2,2-bipyridine with polyethylene glycol) (M =2800, PDI=1.05), which was activated with /V,/V-carbonyldiimidazole (Scheme 19)." Applications in solid electrolytes for DSSC was proposed. Polyester 35 was incorporated with... 

An interesting technical development is related to the use of polymers in photovoltaic devices. This applies to semiconducting polymers [265-272], and typical examples of relevant polymers are listed in Table 3.29. 

In low-dimensional systems, such as quantum-confined. semiconductors and conjugated polymers, the first step of optical absorption is the creation of bound electron-hole pairs, known as excitons [34). Charge photogcncration (CPG) occurs when excitons break into positive and negative carriers. This process is of essential importance both for the understanding of the fundamental physics of these materials and for applications in photovoltaic devices and photodctcctors. Since exciton dissociation can be affected by an external electric field, field-induced spectroscopy is a powerful tool for studying CPG. 

Several attempts to use otganic polymeric semiconductors as the active component in photovoltaic devices have been reported during the last two decades. Interest in the photovoltaic properties of conjugated polymers like polyacelylcne, various derivatives of polythiophenes and poly(para-phenylene vinylene)s arose from... 

Murray et al. [76] have demonstrated that an ionic liquid can be used as both the growth medium for poly(terthiophene) and also as a route to incorporation of anionic dyes into the polymer, for use in photovoltaic devices. Again, the solubility of terthiophene in [NTf2]-based ionic liquids is demonstrated 1.6 x 10-2 M in... 

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a particularly popular conducting polymer as it can have good conductivity and stability and has a low band gap, which is pertinent to its use in photovoltaic devices. A number of authors have now studied the electrochemical synthesis of this polymer in different ionic liquids. Lu et al. [77] first demonstrated the use of [C4mim][BF4] to electrodeposit PEDOT onto ITO, and its application in an electrochromic numeric display. 

The use of Pt-acetylides containing phosphine ligands was extended further by the Schanze group in 2006 [84, 85], In one contribution, they incorporated platinum-acetylide polymers into photovoltaic devices which demonstrate good device efficiency. Transient absorption studies provide definitive evidence for photoinduced electron transfer from the Pt-acetylide to PCBM by the temporal evolution of the TA spectrum, observing the formation of the PCBM radical anion at 1,050 nm. The same system was eventually demonstrated to operate as a bulk heterojunction photovoltaic device [84],... 

In contrast, SchUinsky et al. and Waldauf et al. used an extended numerical description according to the p-n jimction model and demonstrated as well a proper description of hght intensity-dependent device current-voltage characteristics [ 127,157,158]. Thus, several numerical models for the electrical description of polymer-fullerene photovoltaic devices have been presented in the literature to date, and there is an ongoing discussion in the scientific community about them. 

Fig. 58 Schematic of inferred structure for CdSe nanocrystal infiltrated polymer brush photovoltaic device. From bottom to top ITO-coated glass slide modified by surface attachment of a bromine end-capped trichlorosilane self-assembled monolayer (SAM) (squares) polymer brushes grown from the SAM (lines) CdSe nanocrystals infiltrated into the brush network exhibiting some degree of phase separation in the plane of the film (small circles) and an aluminum cathode cap. (Reprinted with permission from [256], 2005, American Chemical Society)...

Drees M, Premaratne K, Graupner W, Heflin JR, Davis RM, Marciu D, Mfller M (2002) Creation of a gradient polymer-fullerene interface in photovoltaic devices by thermally controlled interdiffusion. Appl Phys Lett 81 1... 

It is certain that electrically conductive polymers have attracted much attention in the field of solid state science in recent years. They are expected to have convenient function in the production of useful electric or electronic devices such as the electrodes in rechargeable batteries, pn-junctions for use in integrated circuits (ICs) or in photovoltaic devices, and so on. In the normal sense, the organic polymers, even the 7r-conju-gated systems having mobile 7r electrons, are typical insulators of poor electrical conductivity and have been utilized as dielectric material. This is considered to be a result of the Peierls transition (Peierls, 1955), namely, a metallic-insulator transition, e.g., for polyacetylene, which is characteristic in the one-dimensional system. This situation is circumvented by the doping technique, in which the electron acceptors or donors... 

Economics. The U.S. Department of Energy (DOE) has estimated that In order to be cost-effective, the Installed system price for residential photovoltaic systems In 1986 must be 1.60 to 2.20 per peak watt. In 1980 dollars. Of this, 0.80 per peak watt Is applied to the photovoltaic collector Itself. Typical costs for current photovoltaic systems are 20.00 per peak watt, of which 10.50 per peak watt Is allocated to the collector.( 1) Although strides are being made In the development of singlecrystal silicon photovoltaic devices, the potential for their low-cost manufacture remains an open question. The need to search for other materials which may result In cost-effective devices Is evident. The economic attraction of an organic polymer-based photovoltaic device Is Its use of small amounts of Inexpensive material and Its suitability for mass production. 

Poly-3-hexylthiophene is also a polymer of great interest, widely used in organic electronics, especially in photovoltaic devices. Fabrication of poly-3-hexylthiophene/ polyethylene oxide nanofibers (P3HT-PEO) with diameters down to 500 nm using... 

Electrochemical reaction usually consists of a blend of two materials an electron-donor TT-conjugated polymer (donor, D) and an electron-acceptor fullerene derivative (acceptor, A). Polymers with electrochemical properties have attracted considerable attention over past decades due to potential applications in various fields including low-cost, lightweight, and flexible electrode materials in photovoltaic devices, such as, solar cells and energy storage devices like supercapacitors (Ripolles-Sanchis et al., 2013 Gelinck et al, 2010 Snook etal, 2011). 

Bella, E, 2015. Polymer electrolytes and perovskites lights and shadows in photovoltaic devices. Electrochhn. Acta 175,151-161. 

D. Gebeyehu, C. J. Brabec, F. Padinger, T. Fromherz, J. C. Hummelen, D. Badt, H. Schindler, N. S. Sariciftci, The Interplay of Efficiency cuid Morphology in Photovoltaic Devices Based on Interpenetrating Networks of Conjugated Polymers with Fullerenes. Synth. Met. 2001,118,1-9. 

H. Friend, W. T. S. Huck, Formation of Nanopatterned Polymer Blends in Photovoltaic Devices. Nano Lett. 2010,10,1302-1307. 

J. Nelson, S.A. Choulis, and J.R. Durrant, Cheffge recombination in polymer/ fullerene photovoltaic devices. Thin Solid Films, 2004.451-452 p. 508-514. 

---