Vol.:(0123456789) 1 3 Applied Physics A (2017) 123:772 https://doi.org/10.1007/s00339-017-1383-6 Bimetallic nanocomposite as hole transport co‑bufer layer in organic solar cell Genene Tessema Mola 1  · Elhadi A. A. Arbab 1 Received: 26 September 2017 / Accepted: 3 November 2017 © Springer-Verlag GmbH Germany, part of Springer Nature 2017 Abstract Silver–zinc bimetallic nanocomposite (Ag:Zn BiM-NPs) was used as an inter-facial bufer layer in the preparation of thin flm organic solar cell (TFOSC). The current investigation focuses on the efect of bimetallic nanoparticles on the performance of TFOSC. A number experiments were conducted by employing Ag:Zn nanocomposite bufer layer of thickness 1 nm at various positions of the device structure. In all cases, we found signifcant improvement on the power conversion efciency of the solar cells. It is also noted that the open circuit voltage of the devices are decreasing when Ag:Zn form direct contact with the ITO electrode and without the inclusion of PEDOT:PSS. However, all results show that the introduction of Ag:Zn nanocomposite layer close to PEDOT:PSS could be benefcial to improve the charge transport processes in the preparation of thin flm organic solar cell. The Ag:Zn BiM-NPs and the device properties were presented and discussed in terms of optical, electrical and flm morphologies of the devices. 1 Introduction Solar cell technologies have been steadily improving to efciently harness environmental friendly and sustainable source of solar energy. Harvesting green energy sources has been a high priority agenda globally at present to save our planet from possible environmental catastrophe due to the use of fossil fuel. Thin-flm organic solar cells, which are the third generation of solar cell technologies, emerged as an alternative technology with attractive features such as cheap device production, fexibility, light weight, etc. As a result, TFOSC has been a hot research topic in the last two decades, particularly in the area of power conversion efciency (PCE) and device stability [1, 2]. An efcient harvesting of photons in a photoactive medium of a thin-flm organic solar cell depend on the nature of the photosensitive material used, the thickness of the active layer, the choice of the bufer layers in the fabrication of devices [3]. The thickness of the photoac- tive medium for the fabrication of thin flm organic solar cell often ranges between 140 and 250 nm which is very thin to capture all the incident photons. On the other hand, making the active layer thicker would result in high series resistances that reduces the photo-generated currents. Therefore, there is always a need to fnd a mechanism to increase the harvesting photons in thin flm solar cells from the possible range of the radiation spectrum. One of the possible mechanisms was to disperse the metallic nanoparticles in an appropriate layer of the device structure that would create not only local plasmon resonance efect (LSPR) but also cause multiple light scat- tering in the medium which then lead to better photon har- vesting. The other areas of interest to enhance photocurrent in TFOSC are to improve the charge collection mechanisms by altering the electrical properties of the hole and electron transport layers. One of the main challenges in conventional TFOSC is the quest for an efective inter-facial and hole transport lay- ers, which can provide Ohmic contact and reduce the series resistance between the photoactive layer and the respective electrode. Several strategies have been employed to enhance the performance of TFOSC to be able to resolve the chal- lenges related to low charge carriers mobilities in organic semiconductor materials. Water soluble conducting polymer, better known as poly(3,4-ethylenedioxythiophene):poly(sty renesulfonate) or PEDOT:PSS, is the most commonly used hole transport layer in the preparation of TFOSC which pos- sesses suitable properties such high transparency, optimum work function, smoothness and good conductivity [4, 5]. However, the acidic nature of PEDOT:PSS causes corrosion * Genene Tessema Mola genene.mola@gmail.com 1 School of Chemistry and Physics, University of KwaZulu- Natal, Pietermaritzburg Campus, Private Bag X01, Scottsville 3209, South Africa