A₁‐A₂ Type Wide Bandgap Polymers for High‐Performance Polymer Solar Cells: Energy Loss and Morphology

Abstract

Introducing electron‐withdrawing groups onto donor‐acceptor (D‐A) type conjugated materials is a commonly used method for lowering their highest occupied molecular orbital (HOMO) energy level to achieve higher open circuit voltage (Voc) in polymer solar cells (PSCs). However, this method is rather costly due to the tedious synthesis and low yield involved in preparing the target monomers. Here, a novel design concept of using two different acceptor units to construct acceptor1‐acceptor2 (A1‐A2) type polymers with a deep HOMO level is proposed. Two A1‐A2 type wide bandgap (WBG) polymers, PB24‐3TDC and PB68‐3TDC, were designed for PSCs. The developed polymers possess proper energy levels and complementary absorption with an efficient electron acceptor ITIC‐Th. More importantly, by slightly regulating the alkyl side‐chains, molecular stacking and photoluminescence (PL) emission energy loss of polymers can be alternated significantly. As a result, tuned Voc from 0.9 to 1.0 V and short‐circuit current (Jsc) from 9.4 to 17.0 mA cm−2 can be achieved. The device based on PB24‐3TDC:ITIC‐Th exhibits a higher power conversion efficiency (PCE) of 10.3% compared to PB68‐3TDC:ITIC‐Th based device with a PCE of 7.88%. These results show that the design concept of A1‐A2 type polymer donors have great potential for blending with non‐fullerene acceptors for achieving high performance PSCs.

Horizontal‐, Vertical‐, and Cross‐Conjugated Small Molecules: Conjugated Pathway‐Performance Correlations along Operation Mechanisms in Ternary Non‐Fullerene Organic Solar Cells

“…However, for both the PBDB‐T:SM‐X and PBDB‐T:SM‐XY blends, the emission peak of PBDB‐T still exists to some extent and is even stronger than that of the neat PBDB‐T film excited at 460 nm (Figure S14a, Supporting Information). These results suggest that proficient energy transfer occurs in PBDB‐T:SM‐X and PBDB‐T:SM‐XY blends, but that charge (electron/hole) transfer is involved in the PBDB‐T:SM‐Y blend 6c,e,21. Note that the ITIC:SM‐axis binary blends excited at 460 nm also showed that similar emission trends depend on the type of SM‐axis molecules present, i.e., the energy transfer from SM‐X or SM‐XY to ITIC and charge transfer between ITIC and SM‐Y (Figure b and Figure S14b, Supporting Information).…”

Isomeric Effect of Wide Bandgap Polymer Donors with High Crystallinity to Achieve Efficient Polymer Solar Cells

“…By calculating the dihedral angle, dipole moment, and surface electrostatic potential of isomers, the differences in molecular conformation and electronic properties can be deeply analyzed and thus guide more efficient molecular design. [ 37,38 ]…”

“…moment, and surface electrostatic potential of isomers, the differences in molecular conformation and electronic properties can be deeply analyzed and thus guide more efficient molecular design. [37,38] In this work, fluorinated benzotriazole (ffBTz) and carboxylate-substituted thiophene were used to construct two polymer donors, PBTz4T2C-a and PBTz4T2C-b. The difference between PBTz4T2C-a and PBTz4T2C-b was the substitution position of the carboxylate groups on 4T2C unit.…”

Alkylsilyl Fused Ring‐Based Polymer Donor for Non‐Fullerene Solar Cells with Record Open Circuit Voltage and Energy Loss

“…E loss = E opt -eV OC (where E opt is the optical gap of the absorber, e is the elementary charge) [14][15][16][17][18] . Shockley-Queisser (SQ) theory [19] predicts the theoretical value of 0.25-0.30 eV in the solar cells. However, most of highly efficient OSCs suffer from high E loss in the range of 0.6-1.1 eV, leading to the much lower V OC than inorganic and perovskite solar cells (>1.0 V).…”