Spray deposited carbon nanotube embedded ZnO as an electrons transport layer in inverted organic solar cells

In this report, the synthesis and characterization of ZnO and carbon nanotube (CNT) embedded ZnO composite thin films are presented. The obtained ZnO and CNT composite ZnO thin films are used as an electron transport layer (ETL) for bulk heterojunction (BHJ) inverted organic solar cell (IOSC) with the architecture of ITO/ZnO:CNT/PTB7:PC71BM/MoO₃/Ag. Both ZnO and CNT composite ZnO thin films exhibited a highly preferred c-axis oriented (002) diffraction peak and the peak position is shifted toward a lower angle after embedding CNT into the ZnO matrix. The transmittance slightly decreases after CNT is embedded into the ZnO matrix. Completely wrapped CNT with the ZnO was confirmed by Scanning electron microscope (SEM) measurement. The resistivity of ZnO decreased from 2.02 × 10⁻² to 5.61 × 10⁻³ Ω-cm and mobility increased from 4.30 to 15.24 cm²/V-s after adding CNT into the ZnO matrix. CNT composite ZnO thin film surface is found to be hydrophobic, providing good interfacial contact with the BHJ layer resulting to improve fill factor (FF) of IOSC. The performance of IOSC with CNT composite ZnO ETL layer was significantly improved with a power conversion efficiency of 6.76%, open circuit voltage (V_OC) of 700 mV, short circuit current density (J_SC) of 20.05 mA/cm² and FF of 48.17%, respectively.