OPV cells

OPV cells, as discussed in Section . The necessity of both a nanoporous geometry and an electrolyte for screening of photogenerated electric fields is then described. Finally, some comparisons between DSSCs and other high-surface-area solar cells are drawn. 

Despite the lack of theoretical models for interfacial recombination processes in excitonic solar cells, it is obvious empirically that those cells which function efficiently must have a very slow rate of recombination. In DSSCs, this can be explained simply by the slow electron self-exchange rate of the I /I2 redox couple and the absence of field-driven recombination. However, in the case of solid-state, high-surface-area OPV cells, such as the conducting polymer/C60-derivative cells [36,39], the slow rate of interfacial recombination is an important problem that is not yet understood. 

Organic semiconductor photovoltaic cells share many characteristics with both DSSCs and conventional cells. Charge generation occurs almost exclusively by interfacial exciton dissociation, as in DSSCs, but, in contrast, OPV cells usually contain no mobile electrolyte and thus rely on Vcharge separation. OPV cells may have planar interfaces, like conventional PV cells, or highly structured interfaces, like DSSCs. They provide a conceptual and experimental bridge between DSSCs and conventional solar cells. 

In the future, we see two irreversible trends (1) The cost of solar energy will continue to decrease, and may drop substantially if organic-based photovoltaics (DSSCs and OPV cells), which are much less expensive than inorganic PV, can be made efficient and reliable and (2) the environmental and societal costs... 

The other common OPV cell type, shown in Fig. 1.5b, is the bnlk heterojunction (BHJ) cell, sometimes called the dispersed heterojnnction cell. These cells contain intimate three-dimensional blends of the electron-donating and electron-accepting... 

It would be outside of the scope of this review to address all material functionalities for every type of application. The focus is limited to FETs and transport effects in polymeric OFET. Carrier transport is a key property that links materials for all applications. The learning in OLED and OPV devices has been extremely useful in providing guidelines for OFET materials and vice versa. In OLEDs, carriers are injected from the anode and cathode and they move through the polymeric film. Ideally, the rate at which electrons and holes are supplied, i.e., their mobility, should be similar. In OPV cells, carriers are separated and transported to the respective electrodes to create a photocurrent. In OFETs, carriers... 

Another set of BT containing polymers (P47-49) featuring the 4,7-di(thio-phen-2-yl)-2,l,3-benzothiadiazole chromophore unit were synthesized using Suzuki coupling protocol from 4,7-bis(5-bromothiopene-2-yl)-2,l,3-benzothiadiazole. The blends of PCBM with polymers P47, P48 and P49 were used for fabrication of OPV cells and showed PCE of 2.67%, 3.05% and 1.47%, respectively (Scheme 18.1). ... 

Beyond the description of the So Si transitions, more extensive TDDFT calculations can be used to span the entire near-infrared-visible-ultraviolet spectrum. To illustrate this, we turn to an investigation of a series of DA copolymers that have been used in a number of high-performing OPV cells (Fig. 4) [6-8,10-16,18, 70, 100, 147]. Building on the themes of previous studies, it is of interest to determine whether these copolymers present any intrinsic properties that make them stand out against other less successful DA constructs. 

However, it is worth noting that there is no single observation arising from the study indicative as to why these materials behave so well in OPV cells vs other DA copolymers. 

An example of the modeled electric field intensity profiles of an opaque cell and the corresponding ST-OPV cell are given in Figure 12.3(a). The ST-OPV presented is composed of a PBDTTT-C-T PC7iBM BHJ film sandwiched between an ITO and an ultrathin Ag film (12 nm) transparent electrode, while for the opaque cell a thick Ag film was used as the mirror electrode. The simulations indicate that in both cases the distributions of the electric field inside the solar cells are highly wavelength dependent and inhomogeneous... 

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