Abstract
Stability concerns of organic solar cell devices have led to the development of alternative hole transporting layers such as NiO which lead to superior device life times over conventional Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) buffered solar cells. From the printability of such devices, it is imperative to be able to print NiO layers in the organic solar cell devices with normal architecture which has so far remained unreported. In this manuscript, we report on the successful ink-jet printing of very thin NiO thin films with controlled thickness and morphology and their integration in organic solar cell devices. The parameters that were found to strongly affect the formation of a thin yet continuous NiO film were substrate surface treatment, drop spacing, and substrate temperature during printing. The effect of these parameters was investigated through detailed morphological characterization using optical and atomic force microscopy and the results suggested that one can achieve a transmittance of ~89% for a ~18 nm thin NiO film with uniform structure and morphology, fabricated using a drop spacing of 50 μm and a heat treatment temperature of 400 °C. The devices fabricated with printed NiO hole transporting layers exhibit power conversion efficiencies comparable to the devices with spin coated NiO films.
Highlights
Organic solar cells (OSC) are third generation photovoltaic devices which are being extensively researched due to their potential for flexible, low cost photovoltaic devices which could potentially be produced using manufacturing techniques such as printing technologies[1,2,3]
The results suggest that there are not substantial differences between the transmission characteristics of spin coated NiO films and inkjet printed films with spin coated films showing slightly better transmission above ca. 540 nm while printed NiO films are optically slightly more transparent in the region above 520–550 nm with maximum transmittance at ~89% at 590 nm of the films heat treated at 400 °C
We measured the optical absorbance of P3HT:PC60BM (70 nm) as active layer which was spin coated on 18 nm thin printed NiO film as well as 10 nm thin spin coated NiO films on indium tin oxide (ITO)/Glass substrates
Summary
Organic solar cells (OSC) are third generation photovoltaic devices which are being extensively researched due to their potential for flexible, low cost photovoltaic devices which could potentially be produced using manufacturing techniques such as printing technologies[1,2,3]. Solar cell device is strongly affected by various attributes of these interlayers, for example the charge collection efficiency of the interlayer depends on its work function[12,13,14,15] and conductivity[16] as well as energy level alignment of the interlayer with the lowest occupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) of the materials across the heterojunction[17,18,19,20,21]. Critical is the control of thickness at thicknesses as low as 20–30 nm which makes it a challenging task as one requires control of both uniformity and morphology and a detailed understanding of the process is required
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