Defect-Passivated ZnO via Carboxyl-Functionalized Imides for Efficient and Stable Inverted Organic Solar Cells

Area of Science:

• Materials Science
• Photovoltaics
• Organic Electronics

Background:

• Conventional organic solar cells (OSCs) face stability limitations despite high power conversion efficiency (PCE).
• Inverted OSCs using inorganic oxides like zinc oxide (ZnO) offer enhanced stability but suffer from ZnO surface defects and photocatalytic degradation.
• These ZnO issues negatively impact device performance and operational lifetime.

Purpose of the Study:

• To develop a passivation strategy for ZnO electron transport layers (ETLs) in inverted OSCs.
• To improve both the power conversion efficiency (PCE) and operational stability of ZnO-based inverted OSCs.
• To investigate the effects of carboxyl-functionalized imides on ZnO ETLs and their impact on device performance.

Main Methods:

• Design and synthesis of two carboxyl-functionalized imides (NDI-1C and NDI-2C).
• Application of NDI-1C and NDI-2C as passivating agents for ZnO ETLs in inverted OSCs.
• Systematic characterization of ZnO ETLs and device performance, including PCE, charge transport, and stability testing (T80 lifetime).

Main Results:

• NDI-2C-modified ZnO ETLs exhibited reduced trap state density and improved interfacial contact.
• The inverted OSC with NDI-2C-treated ZnO achieved a PCE of 18.9%, outperforming the control device (17.6%).
• The NDI-2C treated device showed significantly improved photostability, with a T80 lifetime of 2300 hours compared to 200 hours for the control.

Conclusions:

• Carboxyl-functionalized imides, particularly NDI-2C, are effective for passivating ZnO ETLs in inverted OSCs.
• This interfacial modification strategy simultaneously enhances the efficiency and long-term stability of ZnO-based inverted OSCs.
• The study presents a promising approach for developing more robust and efficient organic solar cell technologies.