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

Abstract

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 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.

Significant Stability Improvement of Fullerene Organic Photovoltaics via ZnO Film Modification through the Intermittent Spray Pyrolysis Technique

“…Consequently, we observed that 15R- and 30R-based ZnO films possessed the highest surface roughness, which indicates the higher leakage current 32 obtained from A- and D-based devices, as previously discussed in Figure 2 b. It is worth noting that as compared to our previously reported work 8 as well as the work of Jagadamma et al, 14 we found out that the mentioned surface modification performed for the ZnO film in the current work via the intermittent spray pyrolysis approach using low concentration of ZnO solution ( Experimental Methods ) suppressed the surface roughness of the deposited ZnO film, exhibiting better film quality along with providing higher device performance.…”

“…An intermittent spray pyrolysis approach 8 has been used to optimize the deposition of the ZnO film through different numbers of running cycles (R) of the ZnO precursor solution (as described in the Experimental Methods section). We focus our investigation toward modifying the substrate coverage and surface morphology of the ZnO films and pointing out the morphological compact spot where ZnO films can achieve a similar benchmark efficiency along with an improved stability behavior.…”

“…The used spray pyrolysis tool along with the procedure details used to spray the ZnO solution using the intermittent spray pyrolysis approach was described in our previously reported work. 8 In the current work, various numbers of spraying running cycles (R) of 15R, 20R, 25R, and 30R were performed to deposit different thicknesses of the ZnO film. Each intermittently spraying running cycle (1R) step is defined as 7 s of continuous spraying and 3 s of hold, followed by repeating the same attitude till the corresponding number of spraying running cycles required has been sprayed.…”

“… 16 − 19 Furthermore, the ZnO thin film was subjected to various deposition techniques, including spin coating, 13 , 20 atomic layer deposition, 21 inkjet printing, 22 − 24 and spray pyrolysis techniques. 7 , 8 This in turn influences the morphology, substrate coverage, and contact quality (roughness) of the ZnO layer at the interface with the organic absorber blend. These parameters are the most noteworthy factors in identifying the performance and stability of OPV devices.…”

“…The demonstrated PCE values of the fabricated devices are either better than or comparable to those in the previous reports obtained using different ZnO precursor solution concentrations as well as the conventional spin coating technique. 8 , 14 , 15 The insights gained into the significance of the morphology of sprayed ZnO films highly assisted the development of the film quality. 13 , 19 , 25 Hence, in this work, a novel and pioneer record behavior of the iF-OPVs is presented via a significant enhancement of its stability, achieving 12,000 h (16.7 months).…”