Donor organic solar cells

The aim of this chapter is to give a state-of-the-art report on the plastic solar cells based on conjugated polymers. Results from other organic solar cells like pristine fullerene cells [7, 8], dye-sensitized liquid electrolyte [9], or solid state polymer electrolyte cells [10], pure dye cells [11, 12], or small molecule cells [13], mostly based on heterojunctions between phthaocyanines and perylenes [14], will not be discussed. Extensive literature exists on the fabrication of solar cells based on small molecular dyes with donor-acceptor systems (see for example [2, 3] and references therein). 

Fig. 3 Contemporary organic solar cell devices are based on donor/acceptor heterojunction device architectures, (a) Energy level diagram, (b) Planar heterojunction conligmation. (c) Bulk heterojunction configuration...

Fig. 4 Schematic illustration of the processes leading to photocurrent generation in organic solar cells, (a) Photon absorption in Step 1 leads to excitons that may diffuse in Step 2 to the donor/ acceptor (D/A) interface. Quenching of the exciton at the D/A interface in Step 3 leads to formation of the charge-transfer (CT) state. Note that processes analogous to Steps 1-3 may also occur in the acceptor material, (b) Charge separation in Step 4 leads to free polarons that are transported through the organic layers and collected at the electrodes in Steps 5 and 6, respectively, (c) The equilibria involved in Steps 1-4- strongly influence device efficiency...

Fig. 8 Schematic illustration of donor/acceptor energies relevant for charge-transfer in organic solar cells. Straight lines represent ground state binding energies, while wavy lines represent excited state binding energies...

In organic solar cells, the chemical potential must be considered in addition to the electrical potential. For example, the magnitude and polarity of the photovoltage produced by the first modem donor/acceptor OPV device [9] was noted to... 

Fig. 15 Charge-transfer state electroluminescence (EL) for several polymer fullerene blends used in donor/acceptor organic solar cells. Adapted with permission from [184]. Copyright 2009 American Chemical Society...

Deibel C, Strobel T, Dyakonov V (2010) Role of the charge transfer state in organic donor-acceptor solar cells. Adv Mater 22 4097... 

Organic Solar Cells Using Simple Donor-Acceptor Dyads... 

Mihailetchi [134] investigated the open circuit voltage of the bulk heterojunction organic solar cells based on methanol-fullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as electron acceptor and poly[2-methoxy-5(3 ,7 -dimethyloctyloxy)-p-phenylene vinylene] (OC1C10-PPV) as an electron donor. It is known that a single layer device follows the MIM model [166] and the open circuit voltage V0c is equal to the difference in the work functions of the metal electrodes [134], If charges accumulate in the... 

Mihailetchi et al, 2004), when the electrodes of the device make ohmic contacts with the acceptor and donor materials. Progress in nnderstanding the origin of the open-circuit voltage of organic solar cells and its dependence on device parameters will be discussed in Section 7.6.2 below. 

In this section, we review the basic device physics of organic donor-acceptor solar cells and identify the key material and device parameters that should be addressed in order to improve power conversion efficiency. 

Organic solar cell (OSC) efficiencies of 5% were recently achieved on indium tin oxide (ITO)/CuPc/CuPc C6o/C6o/bathocuproine (BCP)/A1 photovoltaic (PV) devices employing donor (D) copper-phtalocyanine (CuPc) and acceptor (A) fullerene C6o materials [1]. However, little is known about how the device performance and electrical properties are influenced by the composition and preparation conditions of the CuPciC blend layer. 

Lemaur, V., Steel, M., Beljonne, D., Bredas, J.L., and Comil, J., Photoinduced charge generation and recombination dynamics in model donor/acceptor pairs for organic solar cell applications A full quantum-chemical treatment, J. Am. Chem. Soc., 127, 6077, 2005. 

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