Donor–Acceptor–Donor Type Cyclopenta[2,1-b;3,4-b′]dithiophene Derivatives as a New Class of Hole Transporting Materials for Highly Efficient and Stable Perovskite Solar Cells

Abstract

Three new donor−acceptor−donor type (D−A−D) hole-transporting materials (HTMs), YC-1−YC-3, based on the 4-dicyanomethylene-4Hcyclopenta [2,1-b;3,4-b′]dithiophene (DiCN-CPDT) core structure endowed with two arylamino-based units as peripheral groups were designed, synthesized, and applied in perovskite solar cells (PSCs). Hole mobility, steady-state photoluminescence, thin-film surface morphology on top of the perovskite layer, and photovoltaic performance for the YC series were systematically investigated and compared with those of Spiro-OMeTAD. It was found that YC-1 exhibited more efficient hole transport and extraction characteristics at the perovskite/HTM interface. Meanwhile, the film of YC-1 showed a homogeneous and dense capping layer coverage on the perovskite layer without any pinholes, leading to the improvement of the fill factor and open circuit voltage. The PSC device based on YC-1 as a HTM exhibited a high power conversion efficiency (PCE) of 18.03%, which is comparable to that of the device based on the benchmark Spiro-OMeTAD (18.14%), and also a better long-term stability with 85% of the initial efficiency retained in excess of 500 h under the condition of 30% relative humidity, presumably due to the hydrophobic nature of the material. This work demonstrates that the dicyanomethylene-CPDT-based derivatives are promising HTMs for efficient and stable PSCs.

Fabrication of Alternating Copolymers Based on Cyclopentadithiophene-Benzothiadiazole Dicarboxylic Imide with Reduced Optical Band Gap: Synthesis, Optical, Electrochemical, Thermal, and Structural Properties

“…The organic layer was collected and dried over MgSO 4 and the solvent was concentrated to afford the product, which was purified by vacuum distillation and gave 1 as a yellow oil (59.30 g, 245 mmol, 82% yield) [22]. 1 H NMR (CDCl 3 , δ): 6.87 (s, 2H). 13 )were combined in a flask.…”

“…The system degassed under argon and anhydrous toluene (100 mL) was added and heated at 115 • C for 24 h. The flask was cooled to RT and the volatiles were removed to obtain the product, which was purified by column chromatography with gradient (petroleum ether, 0-50% DCM) to obtain an orange solid and the product further purified by recrystallization from methanol to afford 3 as orange crystals (9.10 g, 27 mmol, 90% yield) [24]. 1 Synthesis of 3 ,4 -diamino-2,2 :5,2"-terthiophene (4): EtOH (31 mL) and HCl (62 mL, 35%) were added to 3 (3.00 g, 8.86 mmol) in a flask. To this mixture, anhydrous tin (II) chloride (31.00 g, 163.50 mmol) in ethanol (62 mL) was added and stirred at 30 • C for 24 h. The mixture was cooled to RT and put into cold NaOH.…”

“…The solvent was evaporated to afford the product, which purified via chromatography with DCM to afford 5 as blue crystals (1.72 g, 6 mmol, 93% yield) [26]. 1 H NMR (CDCl 3 , δ): 7.59 (dd, 2H, J = 1.0 Hz, 3.5 Hz), 7.34 (dd, 2H, J = 1.0 Hz, 5.0 Hz), 7.12 (dd, 2H, J = 3.5 Hz, 5.0 Hz). 13 17 mmol) were combined in a flask.…”

“…The reaction contents were refluxed for 24 h. The flask was cooled to RT and the solvent was removed to afford the product, which was purified by column chromatography with gradient (petroleum ether, 0-50% DCM) to afford 6 as yellow crystals (2.37 g, 6 mmol, 94% yield) [27]. 1 Synthesis of 4,7-di(thien-2-yl)-2,1,3-benzothiadiazole-5,6-dicarboxylic acid (7): Sodium hydroxide (4.00 g, 100.00 mmol) dissolved in deionized water (30 mL) was added to a flask. To this solution, ethanol (200 mL) and 6 (2.27 g, 5.45 mmol) were added and the reaction contents were refluxed for 24 h. The flask was cooled to RT and deionized H 2 O was added.…”

“…The precipitate was dried under high vacuum to afford 7 as yellow solid (1.80 g, 5 mmol, 85% yield) [28]. 1 Synthesis of 4,7-di(thien-2-yl)-2,1,3-benzothiadiazole-5,6-dicarboxylic anhydride (8): 7 (1.15 g, 2.96 mmol) and anhydrous acetic anhydride (10.00 g, 97.95 mmol) were combined in a flask. The system was evacuated and refilled with argon for three cycles before anhydrous xylene (30 mL) was added.…”