An Efficient Bulk‐Heterojunction Photovoltaic Cell Based on Energy Transfer in Graded‐Bandgap Polymers

Abstract

It is demonstrated that the energy transfer from low‐conjugated (LC) poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene] (MEHPPV) to high‐conjugated (HC) MEHPPV, coupled with significant electron transfer from HC‐MEHPPV to an acceptor species, offers a viable route for an efficient photodiode over a wide spectral range. An enhanced incident‐photon‐to‐current conversion efficiency (IPCE) of 19 % over a wide spectral range and a power‐conversion efficiency (ηP) of 1 % (under monochromatic illumination at λ ∼ 530 nm and a power density of ca. 1 mW cm–2) are achieved in a ternary polymer‐blend film that consists of HC‐MEHPPV (low bandgap), LC‐MEHPPV (high bandgap), and an acceptor polymer, cyanoPPV (CNPPV), in an optimized ratio. The decisive role of the morphology that emerges during phase separation in the polymer blend is demonstrated by wide‐field photocurrent imaging.

Fill factor in organic solar cells

“…(1) [21]. The thickness d also determines the slope ( ¼ mt/d 2 ) of the JV curve (in the range V sat oVoV OC ) [22,23] [24][25][26][27][28] resulting in a lower PCE as compared to P3HT-PCBM (FF $68%) [7] devices which can be attributed to the lower m and consequent field-dependent exciton dissociation rate in PPV systems [28]. Solar cells based on small molecules are also capable of giving high FF (450%) [29].…”

Single particle spectroscopy on composite MEH-PPV/PCBM nanoparticles

“…Leading examples include polymer organic light emitting diodes (PLEDs), field effect transistors (FETs), and organic photovoltaic devices (OPVs), among others [1][2][3][4][5][6][7][8]. The active layer of plastic bulk heterojunction OPVs is typically composed of a conjugated polymer (electron donating molecule) and fullerene derivative such as C 60 or PCBM (electron accepting molecule) [9][10][11][12]. This active layer has a complex nanostructured morphology that is created by mixing the donor and the acceptor molecules into a blend that forms a bicontinuous interpenetrating network resulting in a large interfacial area for photoinduced charge separation [13].…”

Nonuniform Nanowire Doping Profiles Revealed by Quantitative Scanning Photocurrent Microscopy

“…The induced current signal is highly sensitive to electric fields and has been used to characterize contacts in nanowire and carbon nanotube devices, [4][5][6] quantitatively determine electron and hole mobility-lifetime products in CdS nanowires, [7] identify the active region in Si nanowire p-i-n photodetectors, [8] and investigate transport in thin-film organic semiconductors. [9,10] Furthermore, SPCM data has been analyzed to obtain qualitative potential profiles of devices with Schottky contacts. [4] The evolving shape of such profiles with applied gate or source-drain bias can be used to determine the charge depletion width [5] and Schottky barrier height in devices.…”