| dc.description.abstract | In this study, various dithienopyrrole (DTP) and cyclopentadithiophene (CDT)-based donor-acceptor (D-A) type self-assembled monolayers (SAMs) were developed as dopant-free hole transport materials (HTMs), deposited on NiOx film, and applied in inverted tin-based perovskite solar cells (TPSCs).
In the first part of our research, DTP was used as the central core. One end of the core was functionalized with triphenylamine (TPA) as an electron-donating group, while the other end was modified with electron-withdrawing groups, namely cyanoacetic acid (CA), malononitrile (MN), and cyano phosphonic acid (PA), as anchoring groups. As a result, six small molecule materials were synthesized: DTP-MN-b8 (1), DTP-MN-b16 (2), DTP-CA-b8 (3), DTP-CA-b16 (4), DTP-PA-b8 (5), and DTP-PA-b16 (6). The single crystal structure of DTP-CA-b8 was obtained, showing that the planar nature of the DTP core with a long alkyl chain (branch C8H17) relative to the anchoring group facilitates easy molecular alignment and stacking, thereby promoting the formation of a uniform SAM layer on the NiOx/ITO substrate. Among all the SAMs studied, TPSCs fabricated with a combination of DTP-PA-b8 SAM and NiOx exhibited the highest hole mobility and the slowest charge recombination, achieving a high-power conversion efficiency (PCE) of 8.7%, due to the greater absorption energy and stronger chemical bonding of the PA unit compared to the other anchoring units. Compared to the current highest PCE of 8.3% for TPSCs prepared via self-assembled monolayers (SAM), these results are promising.
In the second part of our research, CDT was used as the core to synthesize four X-shaped self-assembled monolayers (SAMs). These molecules had two TPA groups attached at both ends of this core, and two anchoring groups at the other ends. Additionally, phenyl groups were inserted to extend the conjugation length. As a result, four small molecule materials were synthesized: DPCDT-MN (7), DPCDT-CA (8), DPCDT-PE (9), and DPCDT-PA (10).
The electrochemical and optical properties (HOMO/LUMO and Eg) of these materials were measured using differential pulse voltammetry (DPV) and UV-Vis spectroscopy. Thermal stability was assessed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Optimization of these newly developed organic molecular materials for device applications is currently underway. | en_US |