InGaAs/GaAsP quantum wells for hot carrier solar cells Louise C. Hirst a , Markus F¨ uhrer a , Daniel J. Farrell a , Arthur Le Bris b ,Jean-Fran¸cois Guillemoles b , Murad J. Y. Tayebjee c , Raphael Clady c , Timothy W. Schmidt c , Masakazu Sugiyama d , Yunpeng Wang d , Hiromasa Fujii d , Nicholas J. Ekins-Daukes a a Imperial College London, South Kensington, London, UK; b Institut de Recherche et D´ eveloppement sur l’ ´ Energie Photovolta¨ ıque, Paris, France; c School of Chemistry, The University of Sydney, NSW, Australia; d RCAST, The University of Tokyo, Japan ABSTRACT Hot carrier solar cells have a fundamental efficiency limit well in excess of single junction devices. Developing a hot carrier absorber material, which exhibits sufficiently slow carrier cooling to maintain a hot carrier popula- tion under realistic levels of solar concentration is a key challenge in developing real-world hot carrier devices. We propose strain-balanced In 0.25 GaAs/GaAsP 0.33 quantum wells as a suitable absorber material and present continuous-wave photoluminescence spectroscopy of this structure. Samples were optimised with deep wells and the GaAs surface buffer layer was reduced in thickness to maximise photon absorption in the well region. The effect of well thickness on carrier distribution temperature was also investigated. An enhanced hot carrier effect was observed in the optimised structures and a hot carrier distribution temperature was measured in the thick well (14 nm) sample under photon flux density equivalent to 1000 Suns concentration. Keywords: solar cell, high efficiency, hot carrier, quantum well 1. INTRODUCTION A critical objective of photovoltaic (PV) research is to reduce the cost of generating PV electricity such that grid parity can be achieved. This can be approached in two ways: cost reduction and efficiency enhancement. In recent years single junction device efficiency has been incrementally improved towards their fundamental limit (∼31%) and hence, substantial efficiency enhancement can only be achieved through alternative device design. The hot carrier solar cell (HCSC) was first described by Ross and Nozik in 1982. 1 Since then several other authors have presented hot carrier models, 2, 3 clearly demonstrating a theoretical efficiency advantage over single junction devices. The HCSC has not been demonstrated experimentally, however several authors have studied hot carrier absorber materials 4–8 and energy selective contacts. 9–11 The current authors previously demonstrated hot carrier behaviour in the strain-balanced InGaAs/GaAsP quantum well system. 12 In this initial study hot carrier effects could only be observed under levels of incident photon flux which would not be achievable in real-world solar cells. In this paper we present enhanced hot carrier effects under lower levels of incident photon flux than previously reported, achieved through structure optimisation. The samples used in this study have increased well depth. In addition, the width of the GaAs buffer layer on the top surface of the sample has been minimised, dramatically enhancing photon absorption in the well region underneath. This study also investigates the effect of well width on carrier distribution temperature, further guiding structure design and providing insight to the physical mechanisms causing the hot carrier effect. Send correspondence to Louise Hirst E-mail: louise.hirst@imperial.ac.uk, Telephone: +44 2075946682 Physics, Simulation, and Photonic Engineering of Photovoltaic Devices, Edited by Alexandre Freundlich, Jean-Francois F. Guillemoles, Proc. of SPIE Vol. 8256, 82560X © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.910581 Proc. of SPIE Vol. 8256 82560X-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/05/2015 Terms of Use: http://spiedl.org/terms