Organic and nano-structured composite photovoltaics: An overview

Abstract

Organic photovoltaic devices are poised to fill the low-cost, low power niche in the solar cell market. Recently measured efficiencies of solid-state organic cells are nudging 5% while Grätzel’s more established dye-sensitized solar cell technology is more than double this. A fundamental understanding of the excitonic nature of organic materials is an essential backbone for device engineering. Bound electron-hole pairs, “excitons,” are formed in organic semiconductors on photo-absorption. In the organic solar cell, the exciton must diffuse to the donor–accepter interface for simultaneous charge generation and separation. This interface is critical as the concentration of charge carriers is high and recombination here is higher than in the bulk. Nanostructured engineering of the interface has been utilized to maximize organic materials properties, namely to compensate the poor exciton diffusion lengths and lower mobilities. Excitonic solar cells have different limitations on their open-circuit photo-voltages due to these high interfacial charge carrier concentrations, and their behavior cannot be interpreted as if they were conventional solar cells. This article briefly reviews some of the differences between excitonic organic solar cells and conventional inorganic solar cells and highlights some of the technical strategies used in this rapidly progressing field, whose ultimate aim is for organic solar cells to be a commercial reality.

Enhanced photovoltaic conversion efficiency in bulk heterojunction solar cells upon incorporating nanohybridized PbS quantum dots/multiwall carbon nanotubes

“…In all our devices, the P3HT was used as donor with respect to the PCBM and/or nanohybrid of QD/CNT as the acceptor(s). We presume that the V oc can be attributed to the energy difference between the HOMO of P3HT and LUMO of PCBM in our standard cell as it has been reported by other research groups [42][43][44][45][46][47]. Since the value of conduction band of PbS-QDs is consistently aligned with the LUMO value of PCBM [1,14,28] as shown in Figure 7, therefore it is obvious that the V oc of hybrid device -I is consistent with the standard P3HT:PCBM devices.…”

“…Until now, it has been long-debated in literature to address the exact mechanism for the origin of V oc in photovoltaics and has been still under investigation [42][43][44][45][46][47]. However, it can be quantified by the energy difference between the lowest unoccupied molecular orbital (LUMO) of the acceptor -and the highest occupied molecular orbital (HOMO) of the donor -type materials at the heterojunction interface [42][43][44]46,47].…”

Solar cells utilizing small molecular weight organic semiconductors

“…Among the most promising electronic and photonic devices that make up the organic electronics' collection are organic light emitting diodes, [4][5][6] organic transistors, 7,8 and organic photovoltaic (PV) cells. [9][10][11] Within the research area of organic-based PV cells, there are multiple approaches which are all being actively pursued. These various approaches include the dye-sensitized solar cell (DSSC), 12,13 organic/inorganic hybrid cells, 14,15 and organic PV * Correspondence to: Barry P. Rand, Polymer and Molecular Electronics, IMEC, Kapeldreef 75, B-3001 Leuven, Belgium.…”

Porphyrin Based Dye Sensitized Solar Cells

“…Dye-sensitized solar cells (DSSCs) have emerged as an innovative solar energy conversion technology which provides a pathway for the development of cheap, renewable and environmentally acceptable energy production (Gledhill, Scott et al, 2005;O'Regan & Grätzel, 1991;Shaheen, Ginley et al, 2005). A typical DSSC consists of a sensitizing dye chemically anchored to a nanocrystalline wide band gap semiconductor, such as TiO 2 , ZnO or SnO 2 .…”