Abstract
The performance and stability in atmospheric conditions of organic photovoltaic devices can be improved by the integration of stable and efficient photoactive materials as substituent of the chemically unstable poly (3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS), generally used as organic hole transport layer. Promising candidates are p-type transparent conductive oxides, which combine good optoelectronic and a higher mechanical and chemical stability than the organic counterpart. In this work, we synthesize Cu-rich CuCrO2 thin films by aerosol-assisted chemical vapour deposition as an efficient alternative to PEDOT:PSS. The effect of stoichiometry on the structural, electrical, and optical properties was analysed to find a good compromise between transparency, resistivity, and energy bands alignment, to maximize the photovoltaic performances., Average transmittance and bandgap are reduced when increasing the Cu content in these out of stoichiometry CuCrO2 films. The lowest electrical resistivity is found for samples synthesized from a solution composition in the 60–70% range. The optimal starting solution composition was found at 65% of Cu cationic ratio corresponding to a singular point in Hackee’s figure of merit of 1 × 10−7 Ω−1. PBDD4T-2F:PC70BM organic solar cells were fabricated by integrating CuCrO2 films grown from a solution composition ranging between 40% to 100% of Cu as hole transport layers. The solar cells integrating a film grown with a Cu solution composition of 65% achieved a power conversion efficiency as high as 3.1%, representing the best trade-off of the optoelectronic properties among the studied candidates. Additionally, despite the efficiencies achieved from CuCrO2-based organic solar cells are still inferior to the PEDOT:PSS counterpart, we demonstrated a significant enhancement of the lifetime in atmospheric conditions of optimal oxides-based organic photovoltaic devices.
Highlights
We assume that film properties are similar for CuCrO2 films deposited on glass and on ITO-patterned glass, so the samples are identified by the Cu content of the precursor solution, X
The films are Cu-rich compared to the initial solution composition, X, as we previously reported in our work [33]
Raman spectroscopy was employed to investigate the structural properties of the out of stoichiometry CuCrO2 thin films
Summary
Organic solar cells (OSC) have attracted wide interest in the last decades, because they combine photo-activity, limited cost, and the potential large-scale manufacturing [1], with an adequate Power Conversion Efficiency (PCE) as high as 17.3% [2] (certified). Layer (HTL) and the Electron Transport Layer (ETL). These solar cells contain poly (3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) as HTL [3,4]. This polymeric material has been selected due to its solubility in water [5], which allows its synthesis through solution-based processes, and to its high transparency, around 90%
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