CsGeI₃ Perovskite-Based Solar Cells for Higher Efficiency and Stability: An Experimental Investigation

Among the recent developments in photovoltaic technologies, perovskite solar cells (PSCs) have drawn significant attention, owing to their exceptional power conversion efficiency (PCE), cost-effectiveness, and better optoelectronic characteristics. However, the stability and presence of lead (toxicity) in PSCs remains a major challenge to their commercialization. In this study, we experimentally investigated all-inorganic, lead-free CsGeI<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>-based PSCs in an n-i-p configuration. The CsGeI<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films were synthesized using a one-step spin-coating technique and their crystallographic characteristics were analyzed. Furthermore, we fabricated and tested different device architectures incorporating CsGeI<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as the absorber layer with various electron transport layers (ETLs), including TiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>, ZnO, and graphene oxide (GO), while employing MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as the hole transport layer. The resulting device structure was Fluorine doped Tin oxide (FTO)/(TiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/ZnO/GO)/CsGeI<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>/MoS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/Ni). All fabricated devices demonstrated excellent performance, with the TiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>-based ETL device achieving the highest PCE of 10.79%. In addition, incorporating reduced graphene oxide (rGO) as an interface layer on top of the absorber layer further enhanced photovoltaic performance by approximately 3% across all configurations (achieving outstanding efficiency of 13.57%). The hydrophobic nature and high conductivity of rGO suggest its potential as a promising strategy for improving the stability and efficiency of lead-free PSCs in future applications.