Organic Thin Films Based on DPP-DTT:C60 Blends Deposited by MAPLE.

Marcela Socol,Gianina Popescu-Pelin,Nicoleta Preda,Anca Stanculescu,Carmen Breazu,Andreea Costas,Andreea Mihailescu,Gabriela Petre,Gabriel Socol

doi:10.3390/nano10122366

Abstract

The matrix-assisted pulsed laser evaporation (MAPLE) technique was used for depositing thin films based on a recently developed conjugated polymer, poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)] (DPP-DTT) and fullerene C60 blends. The targets used in the MAPLE process were obtained by freezing chloroform solutions with different DPP-DTT:C60 weight ratios, with the MAPLE deposition being carried at a low laser fluence, varying the number of laser pulses. The structural, morphological, optical, and electrical properties of the DPP-DTT:C60 blend layers deposited by MAPLE were investigated in order to emphasize the influence of the DPP-DTT:C60 weight ratio and the number of laser pulses on these features. The preservation of the chemical structure of both DPP-DTT and C60 during the MAPLE deposition process is confirmed by the presence of their vibrational fingerprints in the FTIR spectra of the organic thin films. The UV-VIS and photoluminescence spectra of the obtained organic layers reveal the absorption bands attributed to DPP-DTT and the emission bands associated with C60, respectively. The morphology of the DPP-DTT:C60 blend films consists of aggregates and fibril-like structures. Regardless the DPP-DTT:C60 weight ratio and the number of laser pulses used during the MAPLE process, the current–voltage characteristics recorded, under illumination, of all structures developed on the MAPLE deposited layers evidenced a photovoltaic cell behavior. The results proved that the MAPLE emerges as a viable technique for depositing thin films based on conjugated polymers featured by a complex structure that can be further used to develop devices for applications in the solar cell area.

Highlights

Among all available renewable energy technologies, photovoltaic technology is the most promising due the notable progress achieved in the last years [1,2,3]
The label of the samples based on DPP-DTT:C60 blends (P1–P7) contains the number of laser pulses used during the matrix-assisted pulsed laser evaporation (MAPLE) deposition (7 k, 25 k or 90 k) and the DPP:C60 weight ratio (1:1, 1:2 or 1:3) in the MAPLE target, with the DPP-DTT layer being deposited at 25 k laser pulses
It can be seen that the thickness of the organic thin films deposited by MAPLE are strongly dependent on the number of laser pulses

Summary

Introduction

Among all available renewable energy technologies, photovoltaic technology is the most promising due the notable progress achieved in the last years [1,2,3]. Regarding the influence of the C60 low solubility on the morphology of the MAPLE deposited layers, it must be mentioned that this parameter cannot play a major role in the agglomeration tendency of C60 molecules during the deposition process, taking into account that such effect was observed for thin films based on azomethine oligomers and C60 deposited by MAPLE using dichlorobenzene as a solvent (known as a good solvent for fullerene) In this context, the present work is focused on the deposition of thin films based on DPP-DTT:C60 blends by MAPLE in order to emphasize the potential of this “soft” laser-assisted deposition technique for preparing organic thin films with tailored properties for developing organic photovoltaic devices. Samples with different DPP-DTT:C60 weight ratios were prepared by varying the number of laser pulses used during the MAPLE process in order to evidence the influence of these two experimental parameters on the structural, morphological, and optical properties of the DPP-DTT:C60 thin films and on the electrical performance of the structures developed on these MAPLE-deposited conjugated polymer-fullerene blend layers

Experiment

Results and Discussions

Conclusions