Thiourea-based CdS thin films: structural and optical analysis for photovoltaic applications

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Original abstract

Cadmium sulfide (CdS) thin films were successfully synthesized using thiourea as the sulfur precursor through the spray pyrolysis technique for photovoltaic (PV) applications. The structural, optical, and photoluminescence properties of the films were investigated to assess their suitability as an electron transport layer (ETL) in perovskite solar cells. X-ray diffraction (XRD) analysis confirmed the formation of polycrystalline CdS with a cubic zinc blende structure and a preferred (111) orientation, indicating high crystallinity and phase purity. UV–Vis spectroscopy revealed a direct optical band gap of 2.43 eV, high visible-light transmittance, and a sharp absorption edge, demonstrating excellent transparency for window layer applications. Photoluminescence (PL) measurements showed a sharp near-band-edge emission peak at 620 nm, indicating low defect density, dominant radiative recombination, and superior optical quality. The absence of deep-level emission bands further confirmed minimal trap-state formation due to the controlled sulfur ion release provided by thiourea during film growth. A comparative assessment with conventional ETL materials such as TiO2, ZnO, and SnO2 highlighted the advantages of thiourea-derived CdS, including high transparency, favorable lattice compatibility, efficient charge transport, low processing temperature, and reduced fabrication cost. Based on these findings, a novel perovskite solar cell architecture, FTO/CdS/Perovskite/Spiro-OMeTAD/Au, was proposed. Energy band alignment analysis demonstrated favorable conduction band matching between CdS (−3.8 eV) and MAPbI3 perovskite (−3.9 eV), enabling efficient electron extraction and reduced interfacial recombination. Simulated device performance under AM1.5G illumination yielded a Jsc of 22.5 mA/cm², Voc of 1.10 V, FF of 78.4%, and PCE of 19.4%, confirming the potential of thiourea-derived CdS for high-performance, low-cost perovskite solar cells.

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