Effect of π-conjugated bridges of TPD-based medium bandgap conjugated copolymers for efficient tandem organic photovoltaic cells

Abstract

Conjugated donor (D)-π-acceptor (A) copolymers, PBDT-TPD, PBDT-ttTPD, PBDTT-TPD, and PBDTT-ttTPD, based on a benzodithiophene (BDT) donor unit and thieno [3,4-c]pyrrole-4,6(5H)-dione (TPD) acceptor unit were designed and synthesized with different π bridges via Pd-catalyzed Stille-coupling. The π bridges between BDT and TPD were thiophene in PBDT-TPD and PBDTT-TPD, and 6-alkylthieno[3,2-b]thiophene in PBDTttTPD and PBDTT-ttTPD. The effects of the π bridges on the optical, electrochemical, and photovoltaic properties of the polymers were investigated, in addition to the film crystallinities and carrier mobilities. Copolymers with the 6-alkylthieno[3,2-b]thiophene π-bridge exhibited high crystallinity and hole mobility. Improved Jsc and FF were obtained to increase the overall power conversion efficiencies (PCE) in inverted single organic photovoltaic cells. A PCE of 6.81% was achieved from the inverted single device fabricated using the PBDTT-ttTPD:PC 71 BM blend film with 3 vol% 1,8-diiodooctane. A tandem photovoltaic device comprising the inverted PBDTT-ttTPD cell and a PTB7-based cell as the bottom and top cell components, respectively, showed a maximum PCE of 9.35% with a Voc of 1.58 V, Jsc of 8.00 mA/cm 2 , and FF of 74% under AM 1.5 G illumination at 100 mW/cm 2 . The obtained PCE of the bottom cell and FF of the tandem cell are, to the best of our knowledge, the highest reported to date for a tandem OPV device. This work demonstrates that PBDTT-ttTPD may be very promising in applications in tandem solar cells. Furthermore, 6-alkylthieno[3,2-b]thiophene π-bridge systems in medium bandgap polymers can improve the performance of tandem organic photovoltaic cells.

Dramatic performance enhancement for large bandgap thick-film polymer solar cells introduced by a difluorinated donor unit

“…State-of-the-art double-junction tandem PSCs consist of a front cell with a relatively large bandgap polymer and a back cell with a smaller bandgap polymer [22]. Although hundreds of low or medium bandgap polymers have been developed for PSCs, there are relatively limited choices of highly efficient large bandgap donor polymers [22,[56][57][58][59][60]. Comparing with commonly used large bandgap polymer material P3HT, PffT2-FTAZ exhibit much higher J SC and EQE values while maintaining high FF ($0.7) under similar thickness condition ($250 nm).…”

Well-controlled thieno[3,4-c]pyrrole-4,6-(5H)-dione based conjugated polymers for high performance organic photovoltaic cells with the power conversion efficiency exceeding 9%

“…1, 2a The manufacturing of OPVs involves low cost and less energy than those of inorganic-based PV devices, which means that OPVs should achieve energy payback much sooner than the existing technologies do, which would increase dramatically if their current modest efficiency and lifetime can be improved. 5 As an electron accepting building block (A), the thieno [3,4-c]pyrrole-4,6-(5H)-dione (TPD) moiety was selected because TPD has electron Most polymers for high efficiency devices satisfy three criteria: (i) wellmatched energy level offsets between the polymer and the acceptor (most commonly a fullerene such as PC 71 BM) to ensure suitable charge separation, while maintaining a high open-circuit voltage (V OC ); (ii) appropriate solubility and miscibility in order to achieve an optimal active layer nanostructure; (iii) a small optical band gap, broad absorption spectra, and high extinction coefficient to facilitate solar photon harvesting for a thin active layer, 2 and possession of a structure composed of alternating donor (D) and acceptor (A) moieties, thus having an internal donor-acceptor structure.…”

Double acceptor donor–acceptor alternating conjugated polymers containing cyclopentadithiophene, benzothiadiazole and thienopyrroledione: toward subtractive color organic photovoltaics

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] To tune the optical and electrical properties of the available active materials, new chemical motifs incorporating fused rings and alternating donor-acceptor (D-A) structures in the polymer chain have been designed and synthesized. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Benzothiadiazole (BT) and its analogs have been used as electron acceptor groups in conjunction with various donor units such as cyclopentadithiophene (CPDT); compounds containing these acceptor groups exhibit lower-energy levels and a reduction in the band gap compared with other D-A alternating copolymers. [23][24][25][26][27][28][29] Since the development of poly [4,4- Figure 1), one of the first efficient third-generation donor-type conjugated polymers, …”