Asymmetric Benzotrithiophene-Based Hole Transporting Materials Provide High-Efficiency Perovskite Solar Cells

Abstract

In this study, we synthesized a series of small-molecule benzotrithiophenes (BTTs) and used them as hole transporting materials (HTMs) in perovskite solar cells (PSCs). The asymmetric benzo­[2,1-b:-3,4-b′:5,6-b″]­trithiophene unit was used as the central core to which were appended various donor groups, namely, carbazole (BTT-CB), thieno thiophene (BTT-FT), triphenylamine (BTT-TPA), and bithiophene (BTT-TT). The extended aromatic core in the asymmetric BTT provided full planarity, thereby favoring intermolecular π-stacking and charge transport. The physical, optical, and electrical properties of these small-molecule HTMs are reported herein. BTT-TT displayed good crystallinity and superior hole mobility, when compared with those of the other three HTMs, and formed smooth and uniform surfaces when covering the perovskite active layer. Accordingly, among the devices prepared in this study, a PSC incorporating BTT-TT as the HTM achieved the highest power conversion efficiency (18.58%). Moreover, this BTT-TT-containing device exhibited good stability after storage for more than 700 h. Thus, asymmetric BTTs are promising candidate materials for use as small-molecule HTMs in PSCs.

Stable Perovskite Solar Cells Using Molecularly Engineered Functionalized Oligothiophenes as Low‐Cost Hole‐Transporting Materials

“…Interestingly, the gradual increase in the thiophene core substitution causes further deterioration in device photovoltaic performance as observed in TT-4D and QT-4D (with three and four thiophene substitution, respectively). [51,61] In this case, FF is the main photovoltaic parameter leading to the lower PCE of TT-4D and QT-4D in comparison with BT-4D. The low FF values of TT-4D and QT-4D can be explained with lower conductivity (vide infra) and poor film formation, as observed in the SEM images (Figure S15, Supporting Information).…”

Design of Low Crystallinity Spiro-Typed Hole Transporting Material for Planar Perovskite Solar Cells to Achieve 21.76% Efficiency

“…In sequence, the perovskite coated with spiro-OMeTAD, SC, and ST could reduce the initial intensity to 0.90%, 1.31%, and 2.14%, respectively, reflecting their hole extraction ability from strong to weak, in agreement with the change of J sc values. Furthermore, the PL decaying curves are fitted by a biexponential equation, , in which the fast decay (τ 1 ) represents the carrier extraction to the HTMs primarily, while the second slow decay (τ 2 ) mainly reflects interface recombination losses (Figure b). The fitting parameters are listed in Table S4, and the short lifetime represents the higher efficiency of hole extraction.…”

Light Management through Organic Bulk Heterojunction and Carrier Interfacial Engineering for Perovskite Solar Cells with 23.5% Efficiency

“…To further explore the reasons for the improvement of PSC hole extraction capacity by different HTLs, both hole mobility and hole conductivity were examined by executing space-charge-limited current (SCLC) (Figure 3f) and the twocontact conductivity measurements (Figure 3 g). [42,43] Hole mobility is evaluated by…”