State polymer solar cell devices

After splitting of the exciton at the heterojunction and further separation of the charge-transfer state, the charges (or polarons) need to be transported within the semiconductor materials network to the respective electrodes. Despite the recognition that it is mainly the separation of the charge-transfer states that limits current polymer polymer solar-cell devices, charge transport also has to be considered, because it is another potential loss mechanism. We will briefly cover this topic the interested reader is referred to a recent review by Blom et al. [7]. 

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. 

In this section we review theoretical and experimental results important for understanding the photophysics of polymer solar cells. We examine the states that are involved in the processes of photoinduced charge generation, and present a theoretical framework that describes the separation and recombination of charge-transfer states. Finally, we review the mechanisms for charge formation that operate in a fdm of a single conjugated polymer and the additional mechanisms, relevant to solar cell devices, that occur in binary donor acceptor blends. 

Currently the best-performing heterojunction photovoltaic devices are made from blends of polythiophenes and PCBM [6,106]. Here, the charge-transfer states are stable with respect to triplet excitons, which comes at the cost of modest open-circuit voltages of 0.6V. Recent experimental evidence suggests that the high performance of PCBM polymer solar cells could also be attributed to the kinetic advantage in charge-transfer state separation that these cells have over those made from amorphous polymers. It is... 

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. 

Given the actual scenario, one can state that the emerging field of nanotechnology represents new effort to exploit new materials as well as new technologies in the development of efficient and low-cost solar cells. In fact, the technological capabilities to manipulate matter under controlled conditions in order to assemble complex supramolecular structures within the range of 100 nm could lead to innovative devices (nano-devices) based on unconventional photovoltaic materials, namely, conducting polymers, fuUerenes, biopolymers (photosensitive proteins), and related composites. 

Attaching perylene moieties as side groups allows achievement of high concentration without affecting the electronic structure of the polymer backbone. Putting 16% perylene moieties as side chains predictably results in more efficient energy transfer, observed with polymer 360, both in solution and solid state (emission band at 599 nm). Although no PLED device with 360 has been reported, this material showed excellent performance in solar cells (external photovoltaic QE = 7%, in blend with PPV) [434]. 

Closely related to liquid electrolyte dye-sensitized solar cells (DSSCs, also known as Gratzel cells ) [283,284], the class of soHd-state DSSCs has been developed to improve device stability and reduce complications in the production process [285-288]. Thus, although polymers can be utilized as replacements for sensitizing dyes (as in liquid electrolyte DSSCs) [289-291], the main effort in applying conjugated polymers focuses on soHd-state DSSCs [45,292-298]. With environmentally friendly production of this polymer based solid-state DSSC in mind, a device based on water-soluble polythiophene derivative has been presented as well [299]. 

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