A Narrow‐Bandgap n‐Type Polymer Semiconductor Enabling Efficient All‐Polymer Solar Cells

Abstract

Currently, n‐type acceptors in high‐performance all‐polymer solar cells (all‐PSCs) are dominated by imide‐functionalized polymers, which typically show medium bandgap. Herein, a novel narrow‐bandgap polymer, poly(5,6‐dicyano‐2,1,3‐benzothiadiazole‐alt‐indacenodithiophene) (DCNBT‐IDT), based on dicyanobenzothiadiazole without an imide group is reported. The strong electron‐withdrawing cyano functionality enables DCNBT‐IDT with n‐type character and, more importantly, alleviates the steric hindrance associated with typical imide groups. Compared to the benchmark poly(naphthalene diimide‐alt‐bithiophene) (N2200), DCNBT‐IDT shows a narrower bandgap (1.43 eV) with a much higher absorption coefficient (6.15 × 104 cm−1). Such properties are elusive for polymer acceptors to date, eradicating the drawbacks inherited in N2200 and other high‐performance polymer acceptors. When blended with a wide‐bandgap polymer donor, the DCNBT‐IDT‐based all‐PSCs achieve a remarkable power conversion efficiency of 8.32% with a small energy loss of 0.53 eV and a photoresponse of up to 870 nm. Such efficiency greatly outperforms those of N2200 (6.13%) and the naphthalene diimide (NDI)‐based analog NDI‐IDT (2.19%). This work breaks the long‐standing bottlenecks limiting materials innovation of n‐type polymers, which paves a new avenue for developing polymer acceptors with improved optoelectronic properties and heralds a brighter future of all‐PSCs.

Controlling Molecular Mass of Low-Band-Gap Polymer Acceptors for High-Performance All-Polymer Solar Cells

“…Additionally, the absorption coefficients of PYT series are much higher than those of the efficient polymer acceptors N2200 with a ε of 3.48 3 10 4 cm À1 at 697 nm 20 and DCNBT-IDT (Poly[5,6-dicyano-2,1,3-benzothiadiazole-alt-indacenodithiophene]) with a ε of 6.15 3 10 5 cm À1 at 759 nm, respectively. 66 This analysis indicates that the PYT series-based devices should have great potential to absorb more energy photons, get higher J sc , and offer increased power conversion efficiency, which will be discussed below.…”

High‐Performance All‐Polymer Solar Cells Enabled by n‐Type Polymers with an Ultranarrow Bandgap Down to 1.28 eV

“…As a result of the high DCNBT electron-deficiency and good backbone coplanarity, the resultant polymer DCNBT-IDT showed a narrower bandgap with a higher absorption coefficient in the long-wavelength region compared to the most successful polymer acceptor N2200 in all-PSCs. [49] When applied in all-PSCs, the DCNBT-IDT yielded a PCE of 8.3%. Despite of such promising performance, DCNBT-IDT has a bandgap of 1.43 eV, which is larger than the state-of-the-art small molecule acceptors COi8DFIC and Y6 with E g s of 1.26 and 1.33 eV, respectively.…”

Dual Function Metallo–Organic Assemblies for Electrochromic–Hybrid Supercapacitors

“…Numerous functional organic materials have been developed to produce solar cells, organic field‐effect transistors, spatial light modulators, organic light‐emitting diodes, and electrochromic windows, to name only a few. [ 5–11 ] Although the introduction of several new materials has led to real‐world applications, [ 12 ] to date, the full potential of molecular‐ and polymer‐based devices has not been unlocked. [ 13 ] This issue is partly because of upscaling‐related issues, costs, but also because stability and device integration hamper large‐scale utilization.…”