Experimental Investigation of the Optoelectronic Properties of Carbazole-Based Hole Transport Layers for Photovoltaic Applications

Perovskite solar cells (PSCs) have emerged as a groundbreaking photovoltaic technology, achieving power conversion efficiencies exceeding 25% with the integration of organic small-molecule hole transport materials (HTMs). Despite this significant advancement, large-scale commercialization remains hindered by the high cost of HTMs and the inherent instability of perovskite materials. Among the most widely used HTMs, Spiro-OMeTAD exhibits excellent optoelectronic properties; however, its complex synthesis and costly purification pose major barriers to widespread adoption. Overcoming these challenges requires the development of alternative, cost-effective HTMs with comparable or enhanced performance to improve both the efficiency and stability of PSCs.

This study explores the optoelectronic properties of carbazole-based derivatives as potential HTMs for PSC applications. Thin films were fabricated via the sol–gel spin coating technique on glass substrates, using chlorobenzene as the solvent. The molecular structure of the investigated compounds was confirmed through FTIR analysis, while UV-visible absorption and photoluminescence spectroscopy were employed to assess theiroptical properties. The resulting films exhibited high transparency in the visible spectrum and strong UV absorption, highlighting their suitability for photovoltaic integration. The estimated optical bandgap of the studied compounds was approximately 2.8 eV. Furthermore, a strong green emission in the visible region further underscores their potential for optoelectronic applications.