Nicolas Drolet

Crystalline low band-gap alternating indolocarbazole and benzothiadiazole-cored oligothiophene copolymer for organic solar cell applications

A low band-gap alternating copolymer of indolocarbazole and benzothiadiazole-cored oligothiophene demonstrated balanced crystallinity and solubility; a solar cell combining this polymer with PC(61)BM in a preliminary test demonstrated power conversion efficiencies of 3.6%.

Steady-state and time-resolved studies of 2,7-carbazole-based conjugated polymers in solution and as thin films: determination of their solid state fluorescence quantum efficiencies

The UV–Vis absorption spectra and the luminescence properties of poly(N-octyl-2,7-carbazole) (POC) and poly(N-octyl-2,7-carbazole-alt-9,9-dioctyl-2,7-fluorene) PCF have been investigated in solution and in the solid state (thin films). No aggregate and/or excimer formation has been detected in these polymeric systems. From time-resolved fluorescence measurements in solution and in the solid state, the fluorescence efficiencies of the thin films have been estimated. It is found that the fluorescence efficiencies of these polycarbazoles in the solid state are quenched, as compared to those measured in fluid solutions, but remain relatively high (φF≅0.40), making them promising materials for electroluminescent devices.

Red–green–blue light-emitting diodes containing fluorene-based copolymers

This paper reports the fabrication and evaluation of light-emitting diodes using polyfluorene derivatives as emitter, which cover the entire visible spectral range. Depending on the composition of the copolymers, red (emission peak at 656 nm), green (488 nm) and blue (428 nm) emission was obtained without any excimer formation. The optimization of the device performances has been realized using a multilayered configuration which involves a spin-coated poly(ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDT–PSS) thin film on the ITO anode and an ultrathin lithium fluoride layer next to the Al cathode. These two layers improve the efficiency of the charge injection. Combining this device configuration with some additional charge-transporting molecules, luminances in the range of 50–300 cd m−2 have been obtained.

The role of emissive charge transfer states in two polymer–fullerene organic photovoltaic blends: tuning charge photogeneration through the use of processing additives

The role of charge transfer (CT) states in organic photovoltaic systems has been debated in the recent literature. In this paper the device performances of two structurally analogous polymers PDTSiTTz (also known as KP115) and PCPDTTTz blended with PCBM are investigated, focusing on the effect the processing additive diiodooctane (DIO) has on morphology, charge photogeneration, and, in particular, the CT state characteristics. While DIO has a considerable beneficial effect for PCPDTTTz:PCBM photovoltaic devices, negligible effects are observed for PDTSiTTz:PCBM devices. An emissive CT state able to be quenched by DIO was observed for PCPDTTTz:PCBM, despite relatively small morphological changes. This is only the second instance of CT state quenching by a processing additive to be reported. Formation of an emissive CT state is therefore a loss pathway for PCPDTTTz:PCBM, which can be alleviated through the use of DIO to increase the proportion of CT states that dissociate into free charges. Conversely, the CT state of PDTSiTTZ:PCBM is weak and short-lived, with the DIO having little effect. The CT state dissociates more efficiently for this higher crystallinity system, leading to less evidence of emissive CT state recombination, and high charge photogeneration yields and device efficiencies.

Benzothiadiazole-cored regioregular oligothiophenes as building blocks for novel crystalline low band-gap conjugated polymers with solution processibility

Bulk heterojunction organic solar cells based on conjugated polymers and soluble fullerene derivatives have been intensively studied due to their simple device structure, easy thin-film casting process, low fabrication cost, and high power conversion efficiency. To further enhance the efficiency, it is of paramount importance to develop new p-type polymeric semiconductors with high charge mobility and narrow energy band gaps. In this paper, we report on an innovative way to synthesize low band-gap conjugated polymers with high crystallinity and reasonable solubility for wet process by using electron-acceptor cored regioregular oligothiophenes as building blocks. These novel building blocks can copolymerize with coplanar fused aromatic compounds, such as indolo[3,2-b]carbazole, to form crystalline polymers with enhanced interchain interaction. Two alternating copolymers P(InCzThnBTD) (n = 2-3) synthesized in this work show much narrower optical band gaps than widely used regioregular P3HT. In addition, the first ionization energy of both synthesized polymers remains high at ~5.17 eV, which is important to achieve large open-circuit voltage (Voc) and improve air stability. Remarkably, the bulk heterojunction photovoltaic (PV) cells fabricated from P(InCzTh2BTD) and PC61BM exhibited a promising PV performance with a PCE = 3.6 %, Voc = 0.69 V, Jsc = 9.17 mA/cm2, and FF = 0.57.