Bulk heterojunction solar cell devices

Bulk heterojunction solar cell devices were fabricated by Liu and coworkers, using the copolymers as the electron donor and ([6,6 ]-phenyl-C6i-butyric acid methyl ester) as the electron acceptor. The preliminary research has revealed power conversion efficiencies of 0.17-0.59% under AM 1.5 illumination (100 mW/cm ). 

Blom PWM, Mihailetchi VD, Koster LJA, Markov DE (2007) Device physics of polymer fullerene bulk heterojunction solar cells. Adv Mater 19 1551 Onsager L (1938) Initial recombination of ions. Phys Rev 54 554... 

A series of ruthenium(II) phthalocyanines with one or two pyridyl dendritic olig-othiophene axial substituent(s) have also been reported (compounds 50 and 51) [50], The dendritic ligands absorb in the region from 380 to 550 nm, which complements the absorptions of the phthalocyanine core. This combination results in better light harvesting property and enhancement in efficiency of the corresponding solar cells. The solution-processed photovoltaic devices made with these compounds and fullerene acceptor give efficiencies of up to 1.6%. These represent the most efficient phthalocyanine-based bulk heterojunction solar cells reported so far. 

Fig. 5.17. One-dimensional device scheme for simulating bulk heterojunction solar cells...

Further, the model allows us to estimate electrical losses in the device. Figures 5.18c and d show the local variations in the energy levels and the carrier densities for the bulk heterojunction solar cell for different mobilities. In Fig. 5.18c, balanced mobilities for electrons and holes are assumed, while Fig. 5.18d describes the situation for the case where the electron mobility is higher than the hole mobility. In the latter case recombination is enhanced as seen from the carrier densities, and the performance of the device (Jsc) is significantly lowered. 

First, the drift current is calculated in the case of a constant electrical field, as one would expect for very thin bulk heterojunction solar cells. If the width W of the active layer is similar to the drift length of the carrier, the device will behave as a MIM junction, where the intrinsic semiconductor is fully depleted. The current is then determined by integrating the generation rate G = —dP/dx over the active layer, where P is the photon flux ... 

In this section we discuss a method of controlled material degradation for individual organic semiconductors and also for the blends used in bulk heterojunction solar cells [37]. The degradation is studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and by determining current/voltage characteristics (I/V measurements) of the devices. 

FIG. 3.35. Experimental J—V characteristics of an ITO/PEDOT PSS/PCBM/Au injection limited electron current (triangles) and calculated space charge limited hole current in OC4C10-PPV (circles) for a thickness of L = 170 nm and temperature T = 290 K. The inserted figure represents die device band diagram under the flat band condition of a bulk heterojunction solar cell using Au as a top electrode [65]. 

In two-component charge transfer systems, such as in the bulk-heterojunction solar cells presented here, deviations of the Vgc from the results of pristine single layer or bilayer devices are expected for two reasons first, some part of the available difference in electrochemical energy is used internally by the charge transfer to a lower energetic position on the electron acceptor second, the rela-... 

Recently, the Konarka group achieved power conversion efficiencies of 5.2% for a low band gap polymer-fuUerene bulk heterojunction solar cell, as confirmed by NREL (National Renewable Energy Laboratory, USA). This encourages the practical use of this concept for low cost, large area production of photovoltaic devices. 

Koster LJA, Smiths ECP, Mihailetchi VD, Blom PWM (2005) Device model for the operation of polymer/fullerene bulk heterojunction solar cells. Phys Rev B 72 085205... 

In this spirit, we will smdy the performance of structured PEDOT films in batteries and/or supercapacitors as well as the application of dedoped PT and P3MT in bulk heterojunction solar cells in the near future [12-15]. Furthermore, thenanostructured conjugated polymer films may find application in thermoelectric devices [47-50],... 

Particular emphasis is given to the patterning of quasi ID nanowire and bicontinuous gyroid arrays, both of which are of particular interest for device applications. The first study of these highly ordered electrochemically patterned semiconductor arrays used in a real device application is described in a dye-sensitized bulk heterojunction solar cell. 

Device Models of Bulk Heterojunction Solar Cells. 10-27 The Equivalent Circuit Model Extended One-Diode Model Electric Field-Dependent Dissociation of the Coulomb-Coupled E-H Pairs Numerical Solution to the Drift-Diffusion Equations... 

Device Models of Bulk Heterojunction Solar Cells... 

They reported that these copolymers showed broad absorption curves with long-wavelength absorption maximum around 620 nm and optical band of 1.68 and 1.64 eV for both polymers. Both polymers were studied for photovoltaic response in bulk heterojunction solar cells. They observed an overall power conversion efficiency of 3.15 and 2.60% for the cast polymers. Further improvement led up to 4.06 and 3.35% for the devices based on thermally annealed materials. 

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