Search

Cost-effective, solution-processable organic photovoltaics (OPV) present an interesting alternative to inorganic silicon-based solar cells. However, one of the major remaining challenges of OPV devices is their lack of long-term operational stability, especially at elevated temperatures. The synthesis of a fullerene dumbbell and its use as an additive in the active layer of a PCDTBT:PCBM-based OPV device is reported. The addition of only 20 % of this novel fullerene not only leads to improved device efficiencies, but more importantly also to a dramatic increase in morphological stability under simulated operating conditions. Dynamic secondary ion mass spectrometry (DSIMS) and TEM are used, amongst other techniques, to elucidate the origins of the improved morphological stability.

Photoactive interfaces derived from all organic double cable polymers (O-DCPs) consisting of covalently conjugated photoelectron donor (D) and electron acceptor (A) molecular components are being recognized as promising light energy harvesting systems. Compared to the limitations faced by the fullerene-based electron acceptors, organic non-fullerene acceptors (NFAs) offer superior properties. Expanding the toolbox of all organic DCP molecules, we have developed two distinct DCPs consisting of polythiophene (PTh) photoelectron D covalently conjugated to rhodanine and perylene diimide (PDI) based organic NFAs. Grignard Metathesis (GRIM) polymerization was used to synthesize the PTh copolymer bearing protected pendant hydroxyl groups. The deprotection of pendant hydroxyl groups followed by an esterification reaction with a boronic ester (BE) bearing acid chloride produced the PTh copolymer with pendant BE groups. The subsequent Suzuki coupling reaction with 7-bromo-2,1,3-benzothiadiazole-4-carboxaldehyde (BBTCA) followed by Knoevenagel condensation with 3-ethylrhodanine produced the polythiophene-rhodanine based covalent D–A hybrid (PTh-Rho-CH) DCP. BE functionalized polythiophene (PTh-BE) was separately functionalized with a PDI derivative to synthesize a polythiophene-PDI based covalent D–A hybrid (PTh-PDI-CH) DCP. Both the DCPs exhibited strong fluorescence quenching of the polythiophene component. The synthesized DCPs were employed as the photoactive layers in interdigitated gold electrode-based photodetector devices. The application of PTh-Rho-CH and PTh-PDI-CH as photoactive layers led to a strong enhancement (by a factor of ∼8 and 16, respectively) of photocurrent generation compared to when PTh lacking acceptor species was employed as the photoactive layer. This work systematically contributes to the development of NFA-based DCPs for application in light harvesting and conversion technologies. [ABSTRACT FROM AUTHOR]

A precise picture of the photophysics that determine the efficiency of nonfullerene acceptor (NFA) bulk heterojunction (BHJ) organic solar cells is still missing, yet needed to mitigate the remaining loss channels. Herein, charge carrier generation and recombination dynamics in blends of a novel wide‐bandgap germanium‐containing donor polymer, namely, PEHGeNDT‐BT, paired with either O‐IDTBR or O‐IDTBCN as NFA in BHJ solar cells are investigated by (ultrafast) transient spectroscopy and time‐delayed collection field (TDCF) experiments. Photovoltaic devices yield moderate power conversion efficiencies (PCEs) of 5.3% when using O‐IDTBCN as the acceptor, and only about 2% when using O‐IDTBR as the acceptor, the latter severely limited by its low photocurrent and moderate fill factor (FF) of ≈43%. Time‐resolved photoluminescence experiments reveal limited exciton quenching as one loss channel in O‐IDTBR‐based blends, accompanied by significant geminate recombination further reducing the photocurrent, while field‐dependent charge generation is identified as the origin of the low FF. Geminate recombination is less in the O‐IDTBCN blend and charge generation is field‐independent, leading to improved photocurrent and FF. Carrier drift‐diffusion simulations of the devices' current–voltage (J–V) characteristics confirm that the experimentally determined kinetic parameters and process yields can reproduce the measured J–V curves under steady‐state solar illumination. [ABSTRACT FROM AUTHOR]

Herein, a side chain engineered polythiophene copolymer based organic semiconductor polymer (OSP) with pendant aldehyde groups was synthesized by a combination of Grignard Metathesis (GRIM) polymerization and post-synthetic modifications. The pendant aldehyde groups of OSP (electron donor-D) were covalently conjugated to the pristine C60 (elector acceptor-A) via 1,3-dipolar cycloaddition reaction (i.e., Prato reaction) between the pristine C60 and azomethine ylide formed in situ as a result of the reaction of pendant aldehyde groups and sarcosine. The OSP with pendant aldehyde groups and its covalent conjugate with pristine C60 were fully characterized using FTIR and 1H-NMR spectroscopies. Fluorescence spectroscopic analysis of the synthesized D–A double cable covalent hybrid and physical hybrid derived from the physical mixing of the synthesized OSP and C60 revealed a higher fluorescence quenching in the case of the covalent hybrid. This novel precisely designed D–A hybrid material was employed as the photoactive layer in an interdigitated gold electrode based photodetector where a significant enhancement in photocurrent (>2.5 times) was observed in the devices consisting of photoactive layer derived from the D–A covalent hybrid. This work offers a step forward in the systematic development of D–A covalent hybrids with a precise molecular design to fabricate efficient photovoltaic devices. [ABSTRACT FROM AUTHOR]