Alloyed halide double perovskites: next promising materials as solar absorbers
Jiban Kangsabanik(1), Vipinraj Sugathan(2), Anuradha Yadav(1), Aswani Yella(2), Aftab Alam(1)
(1)Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India and (2) Department of Metallurgical Engineering & Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India.
Solar energy plays an integral role in supplementing the need of renewable energy. Silicon, in its various forms, covers almost 90% of today`s commercial photovoltaic energy production. But manufacturing and installation processes for silicon devices are still quite expensive. As such, finding novel materials for solar cell applications is an elemental part of photovoltaics research. Hybrid Lead halide perovskites (CH3NH3PbI3) are one of the well sought material in recent past. From 3.8% efficiency in 2009,[1] it has now reached an efficiency of 22.1% .[2] Yet, the main negative issues, i.e. stability in external environment and toxicity of Pb remain a concern. This led to a search for alternative materials. Double perovskite materials have gained some attentions recently, but most of these materials either have indirect band gap or direct but large optical band gap. So, the next possible direction is to find a way to either decrease the optically allowed band gaps or to engineer and acheive direct nature of band gap.
We propose a way to make indirect-direct band gap transition via orbital matching by small Pb+2 doping at both B and B` sites in Cs2B(Cu, Ag, Au)B(Sb,Bi,Sc,Y) X6 (X=Cl,Br,I) double perovskites. This kind of doping has helped to change the topology of band structure triggering an optically allowed transition. It also reduces the band gap significantly, bringing it well in the visible region. Simulation reveals comparable/higher absorption coefficient and solar efficiency with respect to the state of the art photovoltaic absorber material CH3NH3PbI3. Our experimentally measured properties for one of the material, Cs2(Ag0.75Pb0.25)(Bi0.75Pb0.25)Br6 agrees fairly well with the theoretical predictions. This material is shown to be even more stable than CH3NH3PbI3, both under the humidity (~55%) and temperature (T=338 K). With better stability and optical properties, we propose these materials to be the next most promising material for solar absorber and help to significantly advance the field of photovoltaic research.[3]
References :
[1] A. Kojima, K. Teshima, Y. Shirai, & T. Miyasaka, Journal of the American Chemical Society, 131(17), 6050-6051 (2009).
[2] Best Research Cell Efficiencies, www.nrel.gov/ncpv/images/efficiency_chart.jpg
[3] J. Kangsabanik, V. Sugathan, A. Yadav, A. Yella, A. Alam, Physical Review Materials, 2(5), 055401, (2018)