Crown Ether-Assisted ZnO for Low-Cost and High-Efficiency Cu2ZnSn(S, Se)4 Solar Cells

In Cu 2 ZnSn(S, Se) 4 (CZTSSe) solar cells, the conventional magnetron-sputtered ZnO (ZnO-SP) suffers from high cost, low efficiency, and interface damage. This study systematically compares sol–gel ZnO (ZnO-SG) and 18C6 crown ether-modified sol–gel ZnO (ZnO-SG-18C6) as interfacial layers. X-ray diffraction (XRD), scanning electron microscope (SEM), AFM, and X-ray photoelectron spectroscopy (XPS) show ZnO-SP has a uniform hexagonal wurtzite structure, whereas ZnO-SG displays an amorphous fibrous morphology with bright/dark striations. Both exhibit similar UV absorption peaks, but ZnO-SG shows broader absorption and double-exponential decay. Density–voltage ( J – V ) tests reveal that ZnO-SG-18C6 increases PCE from 8.5% to 10.6%, surpassing the 9.5% achieved with ZnO-SP. Electrochemical impedance spectroscopy (EIS) analysis shows that the ZnO-SG-18C6 layer reduces carrier recombination, with the charge transfer resistance ( R ct ) increasing by 30%. Transient photocurrent measurements further reveal that it enhances the photocurrent response, achieving a 1.8-fold increase in the peak, which rises to four times under a 70% high duty cycle.This work demonstrates ZnO-SG-18C6 as a low-cost, high-efficiency alternative to ZnO-SP in CZTSSe solar cells.