Stability Enhancement of High-Performance Inverted Polymer Solar Cells Using ZnO Electron Interfacial Layer Deposited by Intermittent Spray Pyrolysis Approach

In this research work, for the first time, stable high-performance inverted polymer solar cells (iPSCs) have been fabricated utilizing facile and low-cost intermittent spray pyrolysis (SP) technique to deposit transparent thin films of zinc oxide (ZnO) as electron interfacial transporting layer (ETL). The performed iPSCs have the structure of ITO/ZnO/PBDTTT-EFT:PC70BM/V2O5/Ag. The thickness diversity of the ETL layer was adjusted by varying the concentration of the ZnO precursor solution, while fixed thicknesses were fabricated for the other layers in the iPSCs. Moreover, the influence of the deposition techniques on the interface roughness, performance, and stability of the devices has been detected and discussed. By increasing the concentration of the ZnO precursor solution as well as the number of spraying running cycles, the 20 thickness and roughness of the ZnO film increase. The highest power conversion efficiency (10%) of the fresh iPSCs with ZnO-SP was obtained by using a ZnO-precursor solution concentration of 1:4 in ethanol with 7 spraying running cycles. This efficiency is almost the same as the iPSCs fabricated ZnO-ETL by the laboratory-scale spin coating (SC) technique that was used as a reference. Furthermore, it was interesting to observe that the stability of the devices intermittently sprayed by ZnO-SP was higher than the controlled reference ones that were fabricated by ZnO-SC. Hence, deep insight studies have been carried out for the fresh and degraded iPSCs using dark current-voltage characteristics and impedance spectroscopy measurements to investigate the electrical parameters for the ZnO film obtained by the SP and SC techniques. The results indicated that the interface roughness between the ZnO and the active layers plays an important role in enhancing light trapping and the light absorbance inside the cell which increases the generated electric current as well as the stability of the devices.

Automated summary

In this research work, stable high-performance inverted polymer solar cells were fabricated for the first time using intermittent spray pyrolysis technique to deposit ZnO films. It was found that the thickness and roughness of the ZnO film have significant effects on the device performance and stability. By adjusting the concentration of the ZnO precursor solution and the number of spray cycles, the optimal efficiency of the iPSCs was achieved.