Organic solar cells bilayer structure

Miller et al reported a composite from a water soluble multiwalled carbon nanotube (MWNT) and polythiophene for bilayer organic solar cells. This composite layer was then combined with C in bilayer structure. Incorporation of MWNTs into the polythiophene increased the FF by 20% with a corresponding improvement of efficiency compared to the polythiophene/CgQ bilayer device containing no MWNTs [144]. As the... 

Another method that was successfully applied for the formation of a nano-structured bulk heterojunction organic solar cell is nanoimprint lithography (NIL). In direct comparison with a flat bilayer organic solar cell design, the nanostructured version exhibited nearly a double increase in solar PCE [119]. 

Kim et al. used NIL to create nanostructured organic solar cells combining the molded polydithiophene derivative TDPDT with PCBM leading to a PCE of 0.8% compared to 0.25% for a bilayer structure [150]. In a similar manner the formation of inorganic nanopillars is reported. Cathodic electrodeposition of CdS, CdSe,... 

The absorption, emission, and redox properties of squaraines make them highly suited for applications as photosensitizers. In view of this, the early studies on squaraines were focused on thin photovoltaic and semiconductor photosensitization properties [1,4,5,91-97], Champ and Shattuck [98] first demonstrated that squaraines could photogenerate electron-hole (e-h) pairs in bilayer xerographic devices. Subsequently, extensive work has been carried out on the xerographic properties of squaraines [2,24,34,47,48,99,100], and these properties have been reviewed recently [11]. In an extensive smdy on the correlation s between cell performance and molecular structure in organic photovoltaic cells, squaraines were found to have much better solar energy conversion efficiencies than a variety of other merocyanine dyes [4,5]. 

As shown in Figure 5.9, randomly mixed polymer-inorganic BHJ and ordered heterojunction (OHJ) are two common structures to prepare hybrid solar cells [44]. Similar to polymer-fullerene BHJ solar cells, polymer-inorganic hybrid BHJ solar cells (Figure 5.9a) can overcome the limitations of bilayer devices having small donor-acceptor interfacial area with inefficient exciton dissociation. NCRs can be surface modified to render them soluble in organic solvents (such as chloroform, toluene and chlorobenzene) to facilitate solution processability. Various surface... 

Figure 18.1 Structural configurations of typical solar cell made on glass substrate with transparent indium tin oxide (ITO) electrode. The active layer can typically have three configurations (1) single organic layer, (2) bilayer (double-layer) heterojunction between donor and acceptor and (3) bulk heterojunction...

The performance of both types of composites in OPVs is still modest as compared to semiconductor-based solar cells. Improvement in the layer morphology and development of low-bandgap organic materials can lead to higher power conversion efficiencies. An estimation of the maximum expectable efficiency of bulk hetero-junction cells predicts that 10% for solar cells will be reached in the next few years, while practical values of 20-25% would be the limits of the best devices, still to be realized [92]. However, even with low but acceptable rj 5%, mass production of low-cost cells will be a nice solution for renewable energy sources. The main and difficult to solve issue is the stability of the devices, which should attain industrial commercialization requirements. Stable operation for more than 4000 h has been reported for P3HT PCBM bilayer structure cells and can be further improved [93]. 

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