High‐Performance Non‐Fullerene Polymer Solar Cells Based on Fluorine Substituted Wide Bandgap Copolymers Without Extra Treatments

Abstract

A new wide bandgap conjugated polymer, PFBZ, based on fluorination thienyl conjugated benzodithiophene (BDT‐2F) as a donor unit and difluorinated benzotriazole (BTz‐2F) as an acceptor unit, was synthesized for non‐fullerene polymer solar cells (PSCs) application. Compared with the analogue based on non‐fluorinated BDT unit (PBZ), PFBZ shows a lower HOMO level, a similar wide optical bandgap with a higher extinction coefficient, and a slightly higher hole mobility. As a result, without any extra treatments, the PFBZ:ITIC‐based device exhibits a higher PCE of 10.4% with Voc of 0.89 V, Jsc of 18.8 mA cm−2, and FF of 62% in comparison with the PCE of 8.0% with Voc of 0.79 V, Jsc of 17.2 mA cm−2, and FF of 59% for PBZ:ITIC‐based devices. Furthermore, the photovoltaic performance of the PFBZ: ITIC‐based devices are relatively insensitive to the thickness of the active layer and the PCE still remains 8.9% with a thickness of up to 200 nm. In addition, the PFBZ: ITIC‐based devices exhibit high tolerance to the thermal annealing, and still show a high PCE of 9.3% with annealing at 150 °C for 1 hour. These results indicate that PFBZ is a promising candidate for the large scale manufacturing and practical application of high efficient PSCs.

Balanced Electric Field Dependent Mobilities: A Key to Access High Fill Factors in Organic Bulk Heterojunction Solar Cells

“…The PCE is related to these parameters by where is the incident light intensity of AM1.5G. Many strategies have been identified to enhance these three factors . For example, many low bandgap polymers have been designed to enhance absorptions in the near infrared region to improve the J sc s .…”

Mapping Nonfullerene Acceptors with a Novel Wide Bandgap Polymer for High Performance Polymer Solar Cells

“…[29] By combining with BDT donor, the weak electron-accepting benzothiadiazole (BTA) has also been extensively employed in constructing numerous WBG polymers for efficient NFA-PSCs. [26,28,30,31] However, in spite of these latter polymers can enable devices to achieve over 11% PCE with ITIC-anlogues, they do not work well with NIR acceptors due to smaller driving force for charge separation due to mismatched HOMO energy levels. [25,26] By introducing fluoro groups on the backbone or modifying the alkyl side-chains, several more efficient WBG polymers have been developed, like J60, J61, J71, J81, and J91.…”

Fluorinated Photovoltaic Materials for High‐Performance Organic Solar Cells

“…As a result, the BTz‐based polymers display a WBG, high crystallinity, high extinction coefficient, and good hole mobility. Consequently, BTz‐based polymer donors have developed rapidly and have been widely used in NBG SM‐acceptor‐based OSCs . Nevertheless, the high HOMO levels of early BTz‐based polymers limit their application in photovoltaic materials.…”