Design of a New Fused‐Ring Electron Acceptor with Excellent Compatibility to Wide‐Bandgap Polymer Donors for High‐Performance Organic Photovoltaics

Abstract

Fused-ring electron acceptors (FREAs) have recently received intensive attention. Besides the continuing development of new FREAs, the demand for FREAs featuring good compatibility to donor materials is becoming more and more urgent, which is highly desirable for screening donor materials and achieving new breakthroughs. In this work, a new FREA is developed, ZITI, featuring an octacyclic dithienocyclopentaindenoindene central core. The core is designed by linking 2,7-dithienyl substituents and indenoindene with small methylene groups, in which the indeno[1,2-b]thiophene-2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile part provides a large and unoccupied π-surface. Most notably, ZITI possesses an excellent compatibility with commercially available polymer donors, delivering very high power conversion efficiencies of over 13%.

Accurate Determination of the Minimum HOMO Offset for Efficient Charge Generation using Organic Semiconducting Alloys

“…[6][7][8] However, this leads to large energy losses (>0.60 eV), as defined by E loss = E g opt − qV oc , (E g opt is the optical bandgap, V oc is the open-circuit voltage, and q is elementary charge), and limits the power conversion efficiency (PCE) to less than 12% [9][10][11][12][13][14] after decades of effort. [22][23][24][25][26][27][28][29][30][31][32][33] For such a material combination, a large ΔE LUMO always exists, which reduces the highest occupied molecular orbital (HOMO) offset [ΔE HOMO = E HOMO(D) − E HOMO(A) ] to minimize energy loss [34][35][36][37] while enhancing the light collection in near-infrared (NIR) [15][16][17][18][19][20][21] To form a complementary absorption, current popular NFA OSCs are based on the combination of a widebandgap donor and a narrow-bandgap acceptor.…”

Recent Progress in Molecular Design of Fused Ring Electron Acceptors for Organic Solar Cells

“…Later, a series of polymer with 2D‐thienyl side‐chains were developed, such as J51, J60, J61, J71 with PCE more than 11% have been reported. PCE of 11.77% with J61 and m ‐ITIC , PCE of 12.54% with J71 and MeIC , and PCE of 13.24% with J71 and ZITI were achieved. Yan and co‐workers developed a novel polymer BDT‐ alt ‐BTz polymer PvBDTTAZ (Figure ), where BTz unit is unusually connected through phenyl group on BDT .…”

“…Zhu and co‐workers reported ZITI ( A44 , Figure ) with an octacyclic core with two sp 3 methylene bridges designed to enhance quinoidal resonance using a similar design principle applied in NITI . The 22‐electron core provided large vacant π‐surface for strong intermolecular interactions.…”

“…PBDB‐T is particularly suitable for narrow bandgap FREAs due to complementary absorption and appropriate energy levels. PCE values more than 12% were achieved for PBDB‐T‐based OSCs with various FREAs . Recently, electron‐withdrawing F or Cl atoms were attached on thiophene side‐chains on BDT to enhance the absorption and lower HOMO levels of PBDB‐T polymer.…”

“…Besides, in low bandgap material thermal population is surged increasing charge carriers and conductivity. Second, FREAs generally exhibit high absorption extinction coefficients than FAs (≈10 3 versus > 10 5 m −1 cm −1 in dilute solution) which can enhance PCE of the device without an increase in device thickness . Third, tunable molecular energy levels to align energy levels with donor materials.…”