Figure shows that increasing the ETM thickness initially improves Voc due to better electron collection, but Jsc and PCE decline beyond a certain point due to higher series resistance and slower electron transport. The optimized thickness for WS2 was found to be 0.015 µm, where the cell exhibited Voc of 0.86 V, Jsc of 35.63 mA/cm², FF of 76.86%, and PCE of 23.43%. These results are consistent with studies emphasizing that thinner ETM layers reduce resistance and enhance charge extraction efficiency , .