Zwitterion Nondetergent Sulfobetaine-Modified SnO₂ as an Efficient Electron Transport Layer for Inverted Organic Solar Cells

Abstract

Tin oxide (SnO2) has been widely accepted as an effective electron transport layer (ETL) for optoelectronic devices because of its outstanding electro-optical properties such as its suitable band energy levels, high electron mobility, and high transparency. Here, we report a simple but effective interfacial engineering strategy to achieve highly efficient and stable inverted organic solar cells (iOSCs) via a low-temperature solution process and an SnO2 ETL modified by zwitterion nondetergent sulfobetaine 3-(4-tert-butyl-1-pyridinio)-1-propanesulfonate (NDSB-256-4T). We found that NDSB-256-4T helps reduce the work function of SnO2, resulting in more efficient electron extraction and transport to the cathode of iOSCs. NDSB-256-4T also passivates the defects in SnO2, which serves as recombination centers that greatly reduce the device performance of iOSCs. In addition, NDSB-256-4T provides the better interfacial contact between SnO2 and the active layer. Thus, a higher power conversion efficiency (PCE) and longer device stability of iOSCs are expected for a combination of SnO2 and NDSB-256-4T than for devices based on SnO2 only. With these enhanced interfacial properties, P3HT:PC60BM-based iOSCs using SnO2/NDSB-256-4T (0.2 mg/mL) as an ETL showed both a higher average PCE of 3.72%, which is 33% higher than devices using SnO2 only (2.79%) and excellent device stability (over 90% of the initial PCE remained after storing 5 weeks in ambient air without encapsulation). In an extended application of the PTB7-Th:PC70BM systems, we achieved an impressive average PCE of 8.22% with SnO2/NDSB-256-4T (0.2 mg/mL) as the ETL, while devices based on SnO2 exhibited an average PCE of only 4.45%. Thus, the use of zwitterion to modify SnO2 ETL is a promising way to obtain both highly efficient and stable iOSCs.

Efficient interface modification via multi-site coordination for improved efficiency and stability in organic solar cells

“…Among the varieties of ETL materials, n-type low WF metal oxides, including ZnO, SnO 2 , and TiO 2 , etc., have been popularly used in OSCs and other organic electronics, such as perovskite solar cells and organic light-emitting diodes. [20][21][22][23][24][25][26] Although significant progress has been achieved based on metal oxide ETLs, the intrinsic drawbacks of such materials lead to unsatisfactory performances and stability, which need further improvements. Specifically, due to the ''Fermi level pinning effect,'' severe charge barriers exist at the interface between the metal oxide ETLs and organic semiconductors, resulting in inefficient charge transfer and accumulation.…”

Coordination‐Induced Defects Elimination of SnO2 Nanoparticles via a Small Electrolyte Molecule for High‐Performance Inverted Organic Solar Cells

“…To further double-check the charge transport performances at the interface between the ETL and the active layer of the i-OSC device, the electrochemical impedance spectroscopy (EIS) was tested. [55][56][57][58] Typically, the clarification of the impedance spectra (IS) is straight linked with the engrafted bias voltage for the i-OSC devices. The photovoltaic cell will mainly conduct under recombination conditions when one manages IS assessments at the V OC , which could be searched in preceding reports.…”

A Compact Electron Transport Layer Using a Heated Tin‐Oxide Colloidal Solution for Efficient Perovskite Solar Cells

“…[9] Following this work, many research groups have reported solution-processed SnO 2 ETLs. [15,16] In particular, Alfa Aesar's aqueous SnO 2 colloidal solution, which was first adopted by Jiang et al, [17] is frequently used for this purpose. [18][19][20][21][22] Despite using the same colloidal solution, optimized deposition conditions reported in the literature, such as dilution conditions or film thicknesses, differ from lab to lab.…”