ARTICLE Copyright © 2013 by American Scientific Publishers All rights reserved. Printed in the United States of America Science of Advanced Materials Vol. 5, pp. 1–8, 2013 (www.aspbs.com/sam) Synthesis, Characterization and Optical Properties of Novel Hierarchical Flower Like Pyrite FeS 2 Particles for Low Cost Photovoltaics Priya Kush 1 , N. C. Mehra 2 , and Sasanka Deka 1, ∗ 1 Department of Chemistry, University of Delhi, Delhi 110007, India 2 Department of Geology, University of Delhi, Delhi 110007, India ABSTRACT Monodispersed air stable hierarchical FeS 2 particles have been synthesized using a green synthesis method in aqueous solution. The as-synthesized particles have been characterized using powder XRD and Raman spectroscopy and confirmed the formation of cubic pyrite phase excluding the possible presence of other Fe–S phases. The newly developed structures have flower like morphology with narrow size distribution as confirmed by TEM, HRTEM and SEM imaging. The specific topological arrangement realized arises from the crystallographic octahedron form and the growth in particularly 111 direction. The overall hierarchical flower like particles are formed from FeS 2 nanosheets by oriented attachment and confirmed by various controlled experiments. Optical studies on thin film and solution (stable nanocrystal ink) show high absorbance in the entire visible and near-IR wavelength making them potential candidate as absorber in solar cells. A typical indirect band gap of FeS 2 is seen with little blue shift due to nanoparticle nature of the building blocks of the hierarchical flowers. KEYWORDS: Nanostructures, Green Synthesis, Iron Pyrite, Photovoltaics, Optical Materials, Nanocrystal Ink. 1. INTRODUCTION One of the most attractive materials among several exam- ples for large-scale future deployment in photovoltaics (PV) is iron pyrite (FeS 2 . FeS 2 could achieve several times the current global annual electricity consumption compared to conventional x-Si solar cell. 1 Iron persulphide or FeS 2 , which is becoming latest interest of research, is a promising semiconductor material with very high absorption coefficient (∼ 10 5 cm −1 , greater than silicon) and an indirect band gap of 0.95 eV (comparable to Si), 2 exceptionally suitable for photovoltaic energy conversion having an adequate minority carrier diffusion length (100– 1000 nm). 3 4 However, controversy arises on the observa- tion of a direct energy transition at 1.03 or 1.38 eV. 2 5 6 The material can be used as an active absorber layer in solar photovoltaics and consists of cheap, abundant and non-toxic elements, which is desirable for the low cost solar device formation. 2 6 Apart from immense promises in photovoltaics, FeS 2 is adapted as a cathode material for lithium batteries, 7 and as depolarizer anode for hydrogen ∗ Author to whom correspondence should be addressed. Email: sdeka@chemistry.du.ac.in Received: xx Xxxx xxxx Accepted: xx Xxxx xxxx production. 8 Even though the first demonstration of pyrite photoelectrochemical and Schottky solar cells were dated back to 1984 by Tributsch 9 with high quantum efficien- cies (∼ 90%) and photocurrents (> 40 mA cm −2 , but with typical drawback of small photovoltages (< 200 mV) 10 11 which was later attributed to sulfur vacancies in the bulk and at the surface. 12 Despite the huge promises that FeS 2 holds and intensive exploration going on, still enhancing the photovoltage and efficiency of pyrite cells requires basic research on the growth, control of morphology, struc- tural and electronic manipulation of pyrite PV films. Hybrid solar cell or nanocrystal ink for solar cell made from iron pyrite nanocrystals may replace the existing expensive solar cell materials despite having compara- tively less efficiency because of the prospect of fabricat- ing inexpensive and large-area photovoltaics cells from cheaper FeS 2 nanocrystals. Photovoltaic devices based on several semiconductor nanocrystals have recently been proposed and demonstrated, for instance Cu 2 ZnSnS 4 , 13 Cu 2 S, 14 CdTe, 15 Cu(In, Ga) (SSe) 2 , 16 Cu 2−x Se 17 etc. Even after being an efficient photovoltaic material, extensive research has not been done yet in the direction of syn- thesis of FeS 2 with hierarchical morphology and appli- cation of hierarchical FeS 2 for photovoltaics either in hybrid solar cell or in solar cell ink. Few recent reports Sci. Adv. Mater. 2013, Vol. 5, No. 8 1947-2935/2013/5/001/008 doi:10.1166/sam.2013.1519 1