p-Type Functionalized Carbon Nanohorns and Nanotubes in Perovskite Solar Cells

The incorporation of p-type functionalized carbon nanohorns (CNHs) in perovskite solar cells (PSCs) and their comparison with p-type functionalized single- and double-walled carbon nanotubes (SWCNTs and DWCNTs) are reported in this study for the first time. These p-type functionalized carbon nanomaterial (CNM) derivatives were successfully synthesized by [2 + 1] cycloaddition reaction with nitrenes formed from triphenylamine (TPA) and 9-phenyl carbazole (Cz)-based azides, yielding CNHs-TPA, CNHs-Cz, SWCNTs-Cz, SWCNTs-TPA, DWCNTs-TPA, and DWCNTs-Cz. These six novel CNMs were incorporated into the spiro-OMeTAD-based hole transport layer (HTL) to evaluate their impact on regular mesoporous PSCs. The photovoltaic results indicate that all p-type functionalized CNMs significantly improve the power conversion efficiency (PCE), mainly by enhancing the short-circuit current density (J_sc) and fill factor (FF). TPA-functionalized derivatives increased the PCE by 12-17% compared to the control device without CNMs, while Cz-functionalized derivatives resulted in a PCE increase of 4-8%. Devices prepared with p-type functionalized CNHs exhibited a slightly better PCE compared with those based on SWCNTs and DWCNTs derivatives. The increase in hole mobility of spiro-OMeTAD, additional p-type doping, better energy alignment with the perovskite layer, and enhanced morphology and contact interface play important roles in enhancing the performance of the device. Furthermore, the incorporation of p-type functionalized CNMs into the spiro-OMeTAD layer increased device stability by improving the hydrophobicity of the layer and enhancing the hole transport across the MAPI/spiro-OMeTAD interface. After 28 days under ambient conditions and darkness, TPA-functionalized CNMs maintained the performance of the device by over 90%, while Cz-functionalized CNMs preserved it between 75 and 85%.