Please use this identifier to cite or link to this item:
|Title:||Effect of local and global structural order on the performance of perylene diimide excimeric solar cells||Authors:||Ye, Tengling
Butt, Hans Jürgen
Floudas, George A.
Keivanidis, Panagiotis E.
|Major Field of Science:||Engineering and Technology||Field Category:||Electrical Engineering - Electronic Engineering - Information Engineering||Keywords:||Charge transport;Excimer;Extraction;Local and global structure;Nonfullerene acceptors;Organic solar cells;Perylene diimides||Issue Date:||27-Nov-2013||Source:||ACS Applied Materials and Interfaces, 2013, vol. 5, no. 22, pp. 11844-11857||Volume:||5||Issue:||22||Start page:||11844||End page:||11857||Journal:||ACS Applied Materials and Interfaces||Abstract:||Herein, we present a detailed study of the structure-function relationship in the organic photovoltaic (OPV) blend film composed of N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and the low energy gap copolymer of poly[4,8-bis-substituted-benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-4-substituted-thieno[3,4-b]thiophene-2,6-diyl] (PBDTTT-E-O). The hierarchical organization in the photoactive layers and in extruded fibers of PBDTTT-E-O:EP-PDI was studied by fluorescence optical microscopy, atomic force microscopy, and wide-angle X-ray scattering (WAXS). WAXS revealed a nanophase-separated structure where PBDTTT-E-O domains of 4.3 nm in size coexist with EP-PDI domains of 20 nm size. Thermal annealing results in an increase of the PBDTTT-E-O domains, but it does not affect the size of the EP-PDI domains. Only the length of the EP-PDI columns in each domain is increased by thermal treatment. The photophysical characterization of the PBDTTT-E-O:EP-PDI layers and the electrical characterization of the corresponding OPV and unipolar carrier devices were performed. The quenching of the EP-PDI excimer luminescence is correlated with the photocurrent generation efficiency of the OPV devices. At high annealing temperatures the EP-PDI columnar length becomes larger than the previously reported diffusion length of the PDI excimer, and fewer excimers dissociate at the EP-PDI/polymer interfaces, leading to reduced photocurrent generation. The charge transport properties of the PBDTTT-E-O:EP-PDI blend film were studied as a function of the active layer microstructure that was tuned by thermal treatment. Thermal processing increases electron mobility, but the poor connectivity of the EP-PDI domains keeps hole mobility six times higher. In respect to the as-spun OPV device, a 3-fold increase is found in the power conversion efficiency of the device annealed at 100 °C. The high surface roughness of the PBDTTT-E-O:EP-PDI photoactive layer impedes the efficient extraction of charges, and a thin and smooth perylene-3,4,9,10-tetracarboxylic bisbenzimidazole overlayer is required for increasing the device performance to a power conversion efficiency (PCE) ∼ 1.7%. The inversion in the polarity of the device contacts resulted in an inverted device with PCE ∼ 1.9%. We provide rational guidelines for the accurate tuning of the layer microstructure in PDI-based photoactive layers of efficient OPV devices. Local disorder in the EP-PDI aggregates is essential (i) for the optimum electron transport that is ensured by the efficient connectivity of the EP-PDI columns in adjacent EP-PDI domains and (ii) for preventing the stabilization of the neutral photoexcitations in the EP-PDI domains in the form of slowly diffusive excimers. The high photocurrent generation efficiency achieved suggests the EP-PDI excimers are formed faster than the activation of triplet states, and photocurrent losses are minimized.||ISSN:||1944-8252||DOI:||10.1021/am4035416||Rights:||© American Chemical Society||Type:||Article||Affiliation :||Fondazione Istituto Italiano di Technologia
Max Planck Institute for Polymer Research
University of Ioannina
|Appears in Collections:||Άρθρα/Articles|
checked on Aug 31, 2020
WEB OF SCIENCETM
checked on Oct 19, 2020
checked on Oct 24, 2020
Items in KTISIS are protected by copyright, with all rights reserved, unless otherwise indicated.