Fluorene-based hole transport materials (HTMs) with terminating thiophene units are explored, for the first time, for antimony sulfide (Sb 2 S 3 ) solar cells. These HTMs possess largely simplified synthesis processes and high yields compared to the conventional expensive hole conductors making them reasonably economical. The thiophene unit-linked HTMs have been successfully demonstrated in ultrasonic spray-deposited Sb 2 S 3 solar cells resulting in efficiencies in the range of 4.7−4.9% with an average visible transmittance (AVT) of 30−33% (400−800 nm) for the cell stack without metal contact, while the cells fabricated using conventional P3HT have yielded an efficiency of 4.7% with an AVT of 26%. The study puts forward cost-effective and transparent HTMs that avoid a post-coating activation at elevated temperatures like P3HT, devoid of parasitic absorption losses in the visible region and are demonstrated to be well aligned for the band edges of Sb 2 S 3 thereby ascertaining their suitability for Sb 2 S 3 solar cells and are potential candidates for semitransparent applications.
New Spiro‐OMeTAD analogues and the simpler “half” structures with the terminated methoxyphenyl and/or carbazolyl chromophores are successfully synthesized under Hartwig–Buchwald amination conditions using commercially available starting materials. New fluorene‐based hole‐transporting materials combined with suitable ionization energies properly align with the valence band of the perovskite absorber. Additionally, these compounds are amorphous, which is an advantage for the formation of homogenous films, as well as eliminate the possibility for films to crystallize during operation of the devices. The most efficient perovskite solar cells devices contain carbazolyl‐terminated Spiro‐OMeTAD analogue V1267 and reach a power conversion efficiency of 18.3%, along with a short‐circuit current density, open‐circuit voltage, and fill factor of 23.41 mA cm−2, 1.06 V, and 74.0%, respectively. Moreover, “half” structures with methoxyphenyl/carbazolyl fragments show excellent long‐term stability and outperform Spiro‐OMeTAD and, therefore, hold a great prospect for practical wide‐scale applications in optoelectronic devices.
Five new star‐shaped carbazole‐based molecules are successfully synthesized from low‐cost, commercially available reagents via a simple one‐step synthesis route. All carbazole derivatives comprise a 3,6‐diaminocarbazole core with carbazole peripheral groups substituted at the 2‐ or 3‐positions and various aliphatic side chains. These molecules are evaluated as hole transporting materials to replace 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) in perovskite solar cells. Power conversion efficiencies of the devices with these carbazole hole transporting layers reach 19.0%, comparable with 19.7% obtained with the spiro‐OMeTAD‐based device. The thermal and operational stability of the candidate molecules are found to depend on the side chain substituents. Two candidate molecules with ethyl side chains show superior thermal stability compared with that of the reference solar cells prepared with spiro‐OMeTAD.
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