Polymer solar cells short circuit current

He, I. Zhong, C. Huang, X. Wong, W.-Y. Wu, H. Chen, L. Su, S. Cao, Y., Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in polymer solar cells. Adv. Mater. 2011, 23, 4636-4643. 

In the previous section on the short-circuit current, it was demonstrated theoretically and experimentally that Isc in conjugated polymer-fullerene solar cells is controlled to a considerable extent by mobility of the majority charge carriers in the cell s active layer [158]. Moreover, activated behavior of charge carrier mobility in conjugated polymers is known to result in higher mobility at higher temperatures (for a review, see [159]). Accordingly,... 

Katz et al. investigated the performance of the polymer solar cells under elevated temperatures in the range of 25-60 °C, which represents real operating conditions due to heating under solar irradiation [122]. While the open circuit voltage ( oc) decreased linearly with temperature, the short circuit current (Jsc) and the fill factor (FF) increased up to about 50 °C, followed by a saturation region (Fig. 28). These effects overcompensated the dropping 7oc and thus the efficiency was maximal for a 50 °C cell temperature [122]. 

Fig. 44 Light intensity dependence of short circuit photocurrent (filled circles) and open circuit voltage of laminated POPT (MEH-)CN-PPV diffuse bilayer polymer solar cells. The scaling factor of the current calculates as 1.02. (Reprinted with permission from [32], 1998, Macmillan Publishers Ltd)...

Roster LJA, Mihailetchi VD, Xie H, Blom PWM (2005) Origin of the light intensity dependence of the short-circuit current of polymer/fullerene solar cells. Appl Phys Lett 87 203502... 

Finally, conjugated materials 40 based on poly(phenylene thiophene) and poly (fluorene thiophene) main chain polymers functionalized with pendant trithiocyanato ruthenium terpyridine complexes were synthesized by the Suzuki coupling reaction. Heterojunction photovoltaic cells with the simple structure ITO/polymer/C-60/Al were fabricated. Under simulated AM1.5 solar light illumination, the short circuit currents, open circuit voltages, and power conversion efficiencies of the photovoltaic cells were measured to be 1.53-2.58 mAcm 2, 0.12-0.24 V, and 0.084-0.12%, respectively [77]. 

Power conversion efficiency is used to evaluate the photovoltaic performances of solar cells, which is defined by dividing the maximum output power with incident power. The parameters of polymer solar cell performance including open-circuit voltage (Vbc). short-circuit current density (/sc) are originated firom the intrinsic properties of the photoactive polymer. For detailed information of the relationship between polymer properties and solar cell performance will be discussed in the following sections. 

Kwon, S., Shim, M., Lee, J.I., Lee, T.-W., Cho, K., Kim, J.K. Ultrahigh density array of CdSe nanorods for CdSe/polymer hybrid solar cells enhancement in short-circuit current density. J. Mato. Chem. 21, 12449 (2011)... 

Keywords Solar cells, organic photovoltaics (OPVs), quantum confinement effect (QCE), conjugated polymers, nanocomposites, blends, quantum dots (QDs), nanocrystals, nanorods, carbon nanotubes (CNTs), graphene, nanoparticles, alternating copolymers, block copolymers, exdton diffusion length, short-circuit current, open-circuit voltage, fill factor, photoconversion efficiency, in-situ polymerization... 

The appearance of these aggregates does not hamper photovoltaic performance of the fullerene/P3HT blends short-circuit currents and FFs of the devices become even improved in some cases. This behavior makes a sharp contrast with the MDMO-PPV/[60]PCBM and P3HT/[60]PCBM systems described above where the formation of numerous PCBM aggregates in the films immediately kills their photovoltaic performance. It might be envisioned that solar cells comprising thiophene or furane-appended fullerene derivatives (I-III) exhibit superior thermal stability because of hampered fullerene/ polymer segregation. Unfortunately, this issue was not addressed in this study. 

A simple model of band location in polymer solar cells is shown in Fig. 6. The term Fermi level ( f) is used as synonym for the chemical potential of the electrons. Since this level, even as a virtual one, is defined only for an equilibrium situation in the dark, the term quasi-Fermi level is used to describe the situation under illumination. On illumination, and if no current flows, the light-induced carriers split the quasi-Fermi levels, where the electron Ep, E-p,n, is essentially that in the polymer, while the hole p, p,p, is in the semiconductor NCs. If the system is short-circuited, there will be a gradual variation in Ep, and Ep n across the absorber (blend layer) [57]. 

The improvement in power conversion efficiency (PCE) of plasmonic solar cells is always an urgent problem and short circuit current density is one of the key factors for the PCE. The improvement in the Jsc of plasmonic solar cells is mainly achieved by the introduction of metallic nanoparticles, such as blending Au nanoparticles into the anodic buffer layer or the interconnecting layer that connects two subcells of the tandem plasmonic solar cells [86]. Compared with the metallic NPs, nanowires (NWs) are superior in terms of improving photocurrent, while most of the metallic NWs introducing in cells reported previously were used for the anodic contact of the cells [87]. The improvement of PCE in bulk heterojunction polymer solar cells with active layer P3HT PCBM by introducing 40 nm Au nanoparticles between ITO and PEDOT PSS layer with various concentrations is also observed by Gao et al. [88]. It has been found that both short-circuit current density and PCE increase from 3.50% to 3.81% with 0.9 wt. % Au NPs due to the localized surface plasmon excitation of Au NPs. 

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