State-of-the-art polymer solar cells

Significant amount of research has been dedicated to two material systems MDMO-PPV PCBM (MDMO-PPV poly(2-methoxy-5-(3, 7 -dimethyl-octyloxy)-l,4-phenylenevinylene)) and RR-P3HT PCBM, which represent the state-of-the-art polymer solar cell technology. Because there are excellent review papers on the MDMO-PPV PCBM system in the literature, in this section we will only focus on the recent improvements in RR-P3HT PCBM system, especially the approaches to optimize the active blend layer for enhancing device efficiency. 

Fullerene/Conjugated Polymer Composite for the State-of-the-Art Polymer Solar Cells... 

Furthermore, the production is expected to be easily scalable. This technology is currently developed by many researchers around the world, but has not yet reached the marketplace. In order for polymer solar cells to become economic their efficiency must be improved. The power conversion efficiency of a solar cell is dictated by three factors (i) the fraction of sunlight that can be absorbed, (ii) the fraction of absorbed photons that lead to extracted charges ( internal quantum efficiency ), and (iii) the energy that is retained by the extracted charges (ideally close to the open-circuit voltage ). In this review we will refer often to factors (ii) and (ui). Their interplay is not well understood and at present these have not both been optimized simultaneously even in state-of-the-art 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). 

Many authors have reported different approaches for incorporation of different metallic NPs in organic solar cells (OSCs) i.e. in the photoactive layer, in the hole transport layer (HTL), at the HTL/photoactive layer interface and at the ITO/HTL interface. Fig. 6 shows the schematic design describing these different approaches. We have reviewed the detail literature of photovoltaic performance parameters of bulk heterojunction organic/polymer solar cell. Table 1, 2, 3, 4 summarizes the state of the art reports i.e., open circuit voltage (Voc), short circuit current density (jsc), fill factor (FF) and power conversion efficiency (ti) of plasmonic enhanced OSC devices with NPs embedded between interfacing layers, NPs in the hole conducting layers, combination of different NPs and NPs in the photoactive layer, respectively. 

With other substitutes group instead of alkyl side chains, the energy levels of acceptor polymer can be modified to match that of donor materials. Fluoro-substituted n-type conjugated polymers were introduced for all-polymer solar cells with the highest reported energy conversion efficiency of 6.71% at the state of art (Jung et al, 2015). 

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