Zhifan Ke

The doping levels of conjugated polymers significantly influence their conductivity, energetics, and optical properties. Recently, a highly conductive n‐doped polymer called poly (3,7‐dihydrobenzo[1,2‐b:4,5‐b′]difuran‐2,6‐dione) (poly(benzodifurandione), n‐PBDF) is discovered, opening new possibilities for n‐type conducting polymers in printed electronics and other fields. Controlling the doping level of n‐PBDF is of great interest due to its wide range of potential applications. Here controlled dedoping and redoping of n‐PBDF is reported and a mechanistic understating of such a process is provided. Dedoping occurs through electron transfer and proton capture, wherein the ionic dopants, tris(4‐bromophenyl)ammoniumyl hexachloroantimonate (Magic Blue), exhibit efficient proton capture ability and stronger interaction with n‐PBDF, resulting in high dedoping efficiency. Moreover, chemically dedoped PBDF can be redoped using various proton‐coupled electron transfer agents. By manipulating the doping levels of n‐PBDF thin films, ranging from highly doped to dedoped states, the system demonstrates controllable conductivity in five orders of magnitude, adjustable optical properties, and energetics. As a result, these characteristics demonstrate the potential applications of n‐PBDF in organic electrochemical transistors and thermoelectrics.

This work illustrates an effective side-chain modification approach using amide functional groups to induce aqueous electroactivity to ProDOT-based electrochromic polymers.

A fused tris(thienothiophene) (3TT) building block is designed and synthesized with strong electron‐donating and molecular packing properties, where three thienothiophene units are condensed with two cyclopentadienyl rings. Based on 3TT, a fused octacylic electron acceptor (FOIC) is designed and synthesized, using strong electron‐withdrawing 2‐(5/6‐fluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)‐malononitrile as end groups. FOIC exhibits absorption in 600–950 nm region peaked at 836 nm with extinction coefficient of up to 2 × 10⁵m^–1 cm^–1, low bandgap of 1.32 eV, and high electron mobility of 1.2 × 10^–3 cm² V^–1 s^–1. Compared with its counterpart ITIC3 based on indacenothienothiophene core, FOIC exhibits significantly upshifted highest occupied molecular orbital level, slightly downshifted lowest unoccupied molecular orbital level, significantly redshifted absorption, and higher mobility. The as‐cast organic solar cells (OSCs) based on blends of PTB7‐Th donor and FOIC acceptor without additional treatments exhibit power conversion efficiencies (PCEs) as high as 12.0%, which is much higher than that of PTB7‐Th: ITIC3 (8.09%). The as‐cast semitransparent OSCs based on the same blends show PCEs of up to 10.3% with an average visible transmittance of 37.4%.

Naphtho[1,2‐b:5,6‐b′]dithiophene is extended to a fused octacyclic building block, which is end capped by strong electron‐withdrawing 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile to yield a fused‐ring electron acceptor (IOIC2) for organic solar cells (OSCs). Relative to naphthalene‐based IHIC2, naphthodithiophene‐based IOIC2 with a larger π‐conjugation and a stronger electron‐donating core shows a higher lowest unoccupied molecular orbital energy level (IOIC2: −3.78 eV vs IHIC2: −3.86 eV), broader absorption with a smaller optical bandgap (IOIC2: 1.55 eV vs IHIC2: 1.66 eV), and a higher electron mobility (IOIC2: 1.0 × 10⁻³ cm² V⁻¹ s⁻¹ vs IHIC2: 5.0 × 10⁻⁴ cm² V⁻¹ s⁻¹). Thus, IOIC2‐based OSCs show higher values in open‐circuit voltage, short‐circuit current density, fill factor, and thereby much higher power conversion efficiency (PCE) values than those of the IHIC2‐based counterpart. In particular, as‐cast OSCs based on FTAZ: IOIC2 yield PCEs of up to 11.2%, higher than that of the control devices based on FTAZ: IHIC2 (7.45%). Furthermore, by using 0.2% 1,8‐diiodooctane as the processing additive, a PCE of 12.3% is achieved from the FTAZ:IOIC2‐based devices, higher than that of the FTAZ:IHIC2‐based devices (7.31%). These results indicate that incorporating extended conjugation into the electron‐donating fused‐ring units in nonfullerene acceptors is a promising strategy for designing high‐performance electron acceptors.

With their rapid development in recent years, organic solar cells hold the exciting potential to be a groundbreaking form of solar harvesting technology. Among these, all-polymer solar cells (all-PSCs) stand out owing to various advantages such as complementary absorption and superior stability. However, the advance of all-PSCs has been greatly impeded by energy level mismatches and unfavorable morphology of the active layer. Here, we report a molecular engineering approach featuring asymmetrical 4-methoxythiophene/thiophene as conjugated side chains of the donor polymer to fine-tune the energy level alignment and phase separation. The corresponding polymer, namely, poly{4-[5-(2-ethylhexyl)-4-methoxythiophen-2-yl]-8-[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b′]dithiophene}-alt-[bis(5-thiophene-2-yl)-5,6-difluoro-2-(2-hexyldecyl)-2H-benzo[d][1,2,3]triazole-4,7-diyl] (PMOT32) exhibited a power conversion efficiency that exceeded 8.5% in all-PSCs with poly{[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (N2200) as the acceptor. PMOT32:N2200 also maintained good photovoltaic performance when processed as a thick film or from non-halogenated solvents. Detailed comparisons with two other polymers with pure thiophene or 4-methoxythiophene as their side chains revealed how these side chains affected the photovoltaic performance via energy level alignment and phase separation.