Enhancement of Efficiency of Perovskite Solar Cells with Hole-Selective Layers of Rationally Designed Thiazolo[5,4- d ]thiazole Derivatives.

We introduce thiazolo[5,4- d ]thiazole (TT)-based derivatives featuring carbazole, phenothiazine, or triphenylamine donor units as hole-selective materials to enhance the performance of wide-bandgap perovskite solar cells (PSCs). The optoelectronic properties of the materials underwent thorough evaluation and were substantially fine-tuned through deliberate molecular design. Time-of-flight hole mobility TTs ranged from 4.33 × 10 -5 to 1.63 × 10 -3 cm 2 V -1 s -1 (at an electric field of 1.6 × 10 5 V cm -1 ). Their ionization potentials ranged from -4.93 to -5.59 eV. Using density functional theory (DFT) calculations, it has been demonstrated that S0 → S1 transitions in TTs with carbazolyl or ditert -butyl-phenothiazinyl substituents are characterized by local excitation (LE). Mixed intramolecular charge transfer (ICT) and LE occurred for compounds containing ditert -butyl carbazolyl-, dimethoxy carbazolyl-, or alkoxy-substituted triphenylamino donor moieties. The selected derivatives of TT were used for the preparation of hole-selective layers (HSL) in PSC with the structure of glass/ITO/HSLs/Cs 0.18 FA 0.82 Pb(I 0.8 Br 0.2 ) 3 /PEAI/PC 61 BM/BCP/Ag. The alkoxy-substituted triphenylamino containing TT ( TTP-DPA ) has been demonstrated to be an effective material for HSL. Its layer also functioned well as an interlayer, improving the surface of control HSL_2PACz (i.e., reducing the surface energy of 2PACz from 66.9 to 52.4 mN m -1 ), thus enabling precise control over perovskite growth energy level alignment and carrier extraction/transportation at the hole-selecting contact of PSCs. 2PACz/ TTP-DPA- based devices showed an optimized performance of 19.1 and 37.0% under 1-sun and 3000 K LED (1000 lx) illuminations, respectively. These values represent improvements over those achieved by bare 2PACz-based devices, which attained efficiencies of 17.4 and 32.2%, respectively. These findings highlight the promising potential of TTs for the enhancement of the efficiencies of PSCs.