Low-Energy-Loss Polymer Solar Cells with 14.52% Efficiency Enabled by Wide-Band-Gap Copolymers

Kui Feng,Jian Yuan,Zhaozhao Bi,Wei Ma,Xiaopeng Xu,Guangjun Zhang,Qiang Peng

doi:10.1016/j.isci.2018.12.027

Abstract

SummaryTwo wide band-gap copolymers poly[4,8-bis(5-(2-butylhexylthio)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-TZNT] (PBDTS-TZNT) and poly[4,8-bis(4-fluoro-5-(2-butylhexylthio)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-TZNT] (PBDTSF-TZNT) based on naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole) (TZNT) and benzo[1,2-b:4,5-b']dithiophene (BDT) with different conjugated side chains have been developed for efficient nonfullerene polymer solar cells (NF-PSCs). The rigid planar backbone of BDT and TZNT units imparted high crystallinity and good molecular stacking property to these copolymers. Using 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (ITIC) as the acceptor, PBDTSF-TZNT devices showed a high Voc of 0.98 V with an Eloss of 0.61 eV. On selecting 3,9-bis(2-methylene-(5,6-difluoro-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b’]-dithiophene (IT-4F) instead of ITIC, the devices maintained the high Voc of 0.93 V with an even lower Eloss of 0.59 eV. The combination of the above-mentioned low Eloss, broadened absorption, better matched energy level, improved crystallinity, and fine-tuned morphology promoted the power conversion efficiency (PCE) of PBDTSF-TZNT:IT-4F devices from 12.16% to 13.25%. Homo-tandem devices based on PBDTSF-TZNT:IT-4F subcells further enhanced the light-harvesting ability and boosted the PCE of 14.52%, which is the best value for homo-tandem NF-PSCs at present.

Highlights

Polymer solar cells (PSCs), which contain a nanophase-separated bicontinuous network of a p-type conjugated polymer donor and an n-type semiconductor acceptor, have received considerable attention owing to their unique prospects for achieving low cost, light weight, and mechanical flexibility in solar energy applications (Cheng et al, 2009; Li et al, 2012; Zhang et al, 2018b)
Besides the issue of complementary absorption, low-lying highest occupied molecular orbital (HOMO) level and appropriate molecular aggregation of the WBG donor are important for achieving high power conversion efficiencies (PCEs) because the HOMO level and molecular packing can directly influence the open-circuit voltage (Voc) and charge carrier mobility (Cai et al, 2017; Li et al, 2018a; Xu et al, 2018b)
Their detailed synthesis procedures are provided in the Supplemental Information

Summary

Introduction

Polymer solar cells (PSCs), which contain a nanophase-separated bicontinuous network of a p-type conjugated polymer donor and an n-type semiconductor acceptor, have received considerable attention owing to their unique prospects for achieving low cost, light weight, and mechanical flexibility in solar energy applications (Cheng et al, 2009; Li et al, 2012; Zhang et al, 2018b). Planar acceptor-donor-acceptor (A-D-A)-type NFAs presented low band gaps (LBGs) with good absorptions, readily tunable energy levels, and superior photovoltaic performance (Cui et al, 2017; Li et al, 2016; Lin et al, 2015a, 2015b, 2016; Lin and Zhan, 2016; Xu et al, 2017; Yan et al, 2018; Zhang et al, 2018b). Among the efficient material systems of WBG copolymers, benzotriazole (BTA)-based donor-acceptor copolymers have received wide research interests Such types of copolymers provide an advantage of incorporating soluble alkyl chains onto the BTA skeleton rather than on the thiophene bridges of other WBG copolymers, which can reduce the steric repulsion between the adjacent segments for more planar p-conjugations (Min et al, 2011; Price et al, 2011).

Methods

Results

Conclusion