Organic solar cell devices

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...

Table 6.5 Chemical structures of semiconducting polymers used in organic solar cell devices [60-66].

Whilst organic solar cell device models may be intended ultimately to help design the most efficient solar cells [206-210], they have proved very useful in exploring fundamental mechanisms [177, 211-214] and in helping to interpret experimental data [47, 50, 54, 58, 74, 88, 215-219]. In the following we will present a series of case studies where simulations of experimental results have allowed us to interpret experimental data better and to understand fundamental physical phenomena. Please see Appendix 3 for a short description of the used software. 

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...

The preceding sections described molecular interactions important in organic solar cells. This section discusses the impact of those interactions on the overall device behavior. Simulated electrical behavior for a typical solar cell is illustrated in Fig. 10. Under forward bias voltages 0 < V < Vqo typical photovoltaic device under illumination supplies power (P = / x V) to the external circuit (cf. lower panel of Fig. 10, dashed trace in first quadrant). The formalism used here implies that, under reverse bias, the organic material is reduced at the anode and oxidized at the cathode, while, under forward bias, the organic material is oxidized at the anode and reduced at the cathode. The short circuit current, J c, is approximately equal to... 

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. 16 Parameters for defining the charge-transfer state energy cx in organic solar cells. Charge-transfer state energy for MDMO-PPV PCBM blend device determined by Fourier transform photocurrent spectroscopy and electroluminescence measurements. Reprinted figure with permission from [188]. Copyright 2010 by the American Physical Society...

Heremans P, Cheyns D, Rand BP (2009) Strategies for increasing the efficiency of heterojunction organic solar cells material selection and device architecture. Acc Chem Res 42 1740... 

Within the vast field of solar cell devices, organic solar cells [258-261] are experiencing important progresses in their conversion efficiencies that will possibly make them, in the near future, a competitive alternative to silicon solar cells. Moreover, this class of solar cells presents several advantages with respect to their inorganic counterpart such as their low-cost production, easy fabrication, and lightweight, all features that could allow for the fabrication of large-area, foldable, and flexible photovoltaic devices. 

Similarly in the case of organic solar cells, the low optical absorbance in the red/near-infrared region of the dyes commonly used in DSSCs such as ruthenium bipyridyl [276] has prompted the incorporation of Pcs in these devices [277,278],... 

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