Efficient organic solar cells with small energy losses based on a wide-bandgap trialkylsilyl-substituted donor polymer and a non-fullerene acceptor

Haijun Bin,Tom P.A Van Der Pol,Junyu Li,Bas T Van Gorkom,Martijn M Wienk,René A.J Janssen

doi:10.1016/j.cej.2022.134878

Abstract

Efficient organic solar cells based on a blend of PBDS-T as a donor polymer and BTP-eC9 as non-fullerene acceptor are presented and characterized. PBDS-T is an alternating copolymer that comprises easily accessible electron-rich trialkylsilyl-substituted benzodithiophene and electron-deficient benzodithiophene-4,8-dione units and that can be efficiently and reproducibly synthesized in high molecular weights, while keeping good solubility. PBDS-T exhibits a strong absorption between 450 and 700 nm and combines a wide optical bandgap of 1.86 eV, with low-lying energy levels, and a face-on molecular orientation in thin films. Organic solar cells prepared by blending PBDS-T with BTP-eC9 show considerable performance when as-cast films are annealed in solvent vapor and present a high open-circuit voltage of 0.86 V, a low photon-energy loss of 0.53 eV, and an internal quantum efficiency of 93%. The power conversion efficiency reaches 16.4%, which − to the best of our knowledge − is the highest for a conjugated polymer comprising trialkylsilyl side chains in combination with a Y6-based non-fullerene acceptor. Specifically, the trialkylsilyl side-chains of PBDS-T reduce synthetic complexity, result in a low energy loss by ensuring low energetic disorder, and provide competitive device performance.

Highlights

Organic solar cells (OSCs) continue to attract significant interest for photovoltaic energy conversion because they combine intrinsic advan tages, including potential low cost and large area manufacturing, lightweight, semi-transparency, and flexibility with a high power con version efficiency (PCE) [1,2,3]
We find that OSCs based on PBDS-T and BTP-eC9 provide PCEs of 16.4% when using a simple post-treatment by solvent vapor annealing (SVA)
We have shown that PBDS-T, an alternating copolymer based on electron-rich BDTSi units with trialkylsilyl side chains and electron-deficient BDD units, provides a wide optical bandgap, a deep highest occupied molecular orbital (HOMO) energy level, and a preferential face-on molecular orientation

Summary

Introduction

Organic solar cells (OSCs) continue to attract significant interest for photovoltaic energy conversion because they combine intrinsic advan tages, including potential low cost and large area manufacturing, lightweight, semi-transparency, and flexibility with a high power con version efficiency (PCE) [1,2,3]. By adopting trialkylsilylsubstituted benzodithiophene units (BDTSi) in copolymers with benzo triazole (BTA) units, efficient donors such as J70, J71, and J101 have been constructed [34,35,37,38] When blending these polymers with ITIC and their derivatives, the photovoltaic devices show high exciton dissociation and charge separation efficiencies, resulting in excellent device performance. In addition to these electronic characteristics, another important advantage of BDTSi is its convenient synthesis involving a short and high-yield synthetic procedure, which is a desir able feature towards commercialization [39]. PBDS-T is a promising low-cost polymer donor for application in efficient OSCs

Synthesis and opto-electronic properties

Photovoltaic properties

Studies on energy loss and charge recombination

Morphology studies

Optical simulations

Conclusions