Zinc oxide and PEIE as electron transport layers: an in-depth investigation of optoelectronic behaviour in inverted organic solar cells
Recommended Citation
Khanam L, Mukherjee U, Srivastava SB, and Singh SP. Zinc oxide and PEIE as electron transport layers: an in-depth investigation of optoelectronic behaviour in inverted organic solar cells. Physica Scripta 2025;100(8):16.
Document Type
Article
Publication Date
8-4-2025
Publication Title
Physica Scripta
Abstract
Understanding the device physics of organic solar cells (OSCs) involves the investigation of various optoelectronic mechanisms, like photogeneration, rsssecombination, transport of charge carriers, and interfacial stability. The PCE and stability of OSC devices (processed in ambient conditions) are significantly influenced by the transport layer materials and their optical, electrical, and structural properties. Analyzing the electrical and optical behavior of charge transport layers is crucial for optimizing device performance. For the inverted-OSC devices, Zinc oxide (ZnO), a widely used ETL, typically requires high-temperature annealing (≥ 150 °C) to achieve sufficient crystallinity and electrical performance. However, this processing temperature poses challenges for flexible substrates and can impact device scalability. Moreover, ZnO exhibits limitations, including a relatively high work function for electron extraction, increasing interfacial resistances, and inferior charge extraction capability. In this study, we report an in-depth comparative investigation of the optoelectronic behavior of inorganic (ZnO) and organic (PEIE) ETLs in inverted-OSC architecture having PTB7-Th: PC71BM as an active layer. PEIE, a solution-processable polymer that requires low-temperature processing (100 °C), offers multiple advantages, including smoother surface morphology, reduced electrical resistances (Rs and Rt), and a lower work function, all of which contribute to enhanced charge extraction and overall device performance. A wide range of characterization techniques, such as atomic force microscopy (AFM), UV—Vis spectroscopy, Ellipsometry, and Scanning Kelvin Probe Microscopy (SKPM), were employed to gain insights into the nanostructural morphology of the thin films, optical characteristics, and the alignment of energy levels at the ITO/ETLs/BHJ active layer interface. In addition to the current (J)-voltage (V) characteristics, the impedance spectroscopic (IS) analysis is conducted for a comparative investigation of the electrical behavior of ZnO (prepared with Zinc acetate dihydrate and Zinc acetate precursors) and PEIE ETLs-based OSCs. The encapsulated devices were recurrently characterized for up to 60 days in ambient conditions to analyze the impact of ETLs on the stability of OSCs. Impedance spectroscopy measurements and Mott-Schottky analysis reveal that the charge carrier dynamics and various electrical parameters exhibit improvements with PEIE ETL compared to ZnO ETLs. The device incorporating PEIE ETL demonstrated notable improvements in key photovoltaic parameters, including a higher Jsc (13.7 mA cm−2), enhanced FF (64.5%), and reduced Rs (6.2 Ω·cm2) compared to ZnO(2) based (Jsc = 13.1 mA cm−2, FF = 62.2%, Rs = 9.1 Ω·cm2) and ZnO(1) based (Jsc = 12.7 mA cm−2, FF = 53.1%, Rs = 10 Ω·cm2) devices. The outcome represents a substantial enhancement, surpassing the efficiencies obtained with ZnO ETLs prepared using anhydrous zinc acetate and zinc acetate dihydrate by 16% and 4%, respectively.
ePublication
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