(Invited) Efficient Non-Fullerene Polymer Solar Cells
Authors: Sanchez Jose G. , Ferré-Borrull Josep , Pallares Josep , Marsal Lluis F. 
Published: February 2020

Polymer solar cell (PSCs) haveattracted much interest in the renewable energy field because of their low-cost manufacturing, light weight, flexibility and large-scale production [1, 2]. Conventional PSCs exhibit poor stability and short operational lifetimes under environment conditions, and thus require complex encapsulation process to reduce degradation under oxygen and moisture [3]. To solve those problems, PSCs with an inverted structure (iPSCs) were developed. In iPSCs, transition metal oxides such molybdenum oxide (MoO3) or vanadium oxide (V2O5) are used as the hole transport layer (HTL). On the other hand, titanium oxide (TiOx) and zinc oxide (ZnO) are used as electron transport layer (ETL) [4, 5]. In recent years, iPSCs with power conversion efficiency (PCE) of 11% has been reported [6]. Although fullerene derivatives (e. g PC71BM and PC61BM), have been widely used as acceptor materials, the interest on non-fullerene acceptors have increased because of their high thermal stability, tunable molecular energy levels, excellent optical absorption properties and low-cost synthesis [7, 8]. In this work, we present the fabrication and the analysis of the performance of iPSCs based on the polymer PBDB-T and the non-fullerene acceptor IT-M. All the devices were fabricated on ITO substrate using TiOx as ETL, while the V2O5/Ag bilayer was used as top cathode. The materials PBDB-T:IT-M were dissolved in a mixture of solvents chlorobenzene and 1,8-diiodooctane (99:0.5 v/v) with the total concentration of 20 mg ml-1. The PBDB-T:IT-M blend solution was spin-cast on top of TiOx at two different velocities to analyze the effect of the active layer thickness (100 and 130nm) on the performance parameters of iPSCs. Moreover, the effects of the annealing temperature (0, 100 and 160ºC) on the performance parameters of PBDB-T:IT-M-based devices are also investigated. Current density–voltage (J–V) characteristics were measured under simulated AM1.5G illumination (100mWcm-2) conditions to calculate the performance parameters [open circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF) and power conversion efficiency (PCE)] of all iPSCs. The devices with an active layer with a thickness of 100nm exhibit higher performance parameter than that of devices with an active layer thickness of 130nm. In both type of devices (active layer thickness of 100 and 130 nm), the performance parameter values decrease as the annealing temperature increases. Devices with an active layer thickness of 100nm and without thermal annealing (0ºC) exhibit the highest performance parameters, VOC= 919 mV, JSC= 16.2 mA cm-2, FF = 67% with an a PCE of about 9.9%. The results demonstrated that iPSCs using non-fullerene acceptor allow to reach efficiencies of about 10% after a manufacturing parameters optimization such as thickness of the active layer and annealing temperature.Moreover, we demonstrated that thermal annealing reduces the performance of these devices. Finally, this work shown the fabrication and characterization of high efficiency PSCs using a non-fullerene acceptor material as a promisingalternative to the fabrication of fullerene-based PSC.
Acknowledgements
This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (MEIC) for grant numbers, TEC2015-71915-REDT and TEC2015-71324-R (MINECO/FEDER), by the ICREA for the ICREA Academia Award, by the Catalan authority for project AGAUR 2017 SGR 1527.
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