Demethylation strategies for spiro-OMeTAD to enhance the thermo-opto-electronic properties as potential hole transport materials in perovskite solar cells

Spiro-OMeTAD is a widely used hole-transporting material (HTM) that plays a crucial role in achieving highly efficient perovskite solar cells (PSCs). In this work, a series of demethylated functionalized spiro-OMeTAD-based derivatives with different numbers of hydroxyl substituted groups (named as SOH2, SOH4, and SOH6) were synthesized, and their thermal, optical, electrical, and electrochemical properties have been investigated as potential HTMs for PSCs. It has been found that the molecule with six hydroxyl substituted groups on the spiro-OMeTAD-based structure SOH6 exhibited the highest glass transition temperature (Tg) and melting point (Tm) as compared to SOH2 and SOH4 molecules. The UV-Vis absorption spectra portrayed a distinct pattern with the increase in hydroxyl substituted groups as it was slightly blue-shifted for the SOH6 molecule compared to red-shifted for SOH2 and SOH4 molecules. Carrier mobility shows a notable improvement with the hydroxyl substitution. The density functional theory (DFT) has provided useful insight into identifying the chemical stability of spiro-OMeTAD derivatives. In the device simulation, hydroxyl substituted spiro SOH2 was found to outperform its pristine counterpart, achieving a peak PCE of 17.61% with a Voc of 0.98 V, a Jsc of 22.69 mA/cm2, and an FF of 80.67% within the device structure FTO/TiO2/MAPbI3/HTMs/Au. This investigation provided insight into the development of novel spiro-OMeTAD-based derivatives with enhanced optoelectronic properties and showed promising potential for addressing the limitations of traditional HTMs in PSCs.