Light trapping in thin silicon solar cells: A review on fundamentals and technologies

Rebecca Saive

doi:10.1002/pip.3440

Abstract

AbstractThin, flexible, and efficient silicon solar cells would revolutionize the photovoltaic market and open up new opportunities for PV integration. However, as an indirect semiconductor, silicon exhibits weak absorption for infrared photons and the efficient absorption of the full above bandgap solar spectrum requires careful photon management. This review paper provides an overview on the fundamental physics of light trapping and explains known theoretical limits. Technologies that have been developed to improve light trapping will be discussed, and limitations will be addressed.

Highlights

Forty years after Eli Yablonovitch submitted his seminal work on the statistics of light trapping in silicon,[1] the topic has remained on the forefront of solar cell research due to the prevalence of silicon in the photovoltaic (PV) industry since its beginnings in the 1970s
This review paper provides an overview of the physics involved in light trapping in solar cells with special focus on crystalline silicon
The Lambertian (4n2) limit was derived, and it was explained how this limit can only be overcome through modification of the local optical density of states (LDOS) within the absorber or within the surrounding air

Summary

| INTRODUCTION

Forty years after Eli Yablonovitch submitted his seminal work on the statistics of light trapping in silicon,[1] the topic has remained on the forefront of solar cell research due to the prevalence of silicon in the photovoltaic (PV) industry since its beginnings in the 1970s.2,3 Despite the rise of a plethora of alternative technologies, more than 90% of newly installed PV plants are still based on silicon.[3]. A rigorous derivation of the open-circuit voltage can, for example, be found in Würfel and Würfel.[29] The open-circuit voltage has been shown to improve with decreasing thickness of silicon (heterojunction) solar cells.[30,31,32,33] Thinning the wafer leads to decreased charge carrier recombination in the bulk[30] and to increased charge carrier concentration—as long as the photocharge carrier generation remains constant and excellent surface passivation is provided— which in turn leads to increased open-circuit voltage.[34,35] Vice versa, if the recombination and dark current remain the same and jSC/j0 ) 1, the difference in opencircuit voltage ΔVOC depends logarithmically on the factor y with which the short-circuit current density changes: ΔVOC kB

Tcell q lnðyÞ

Findings

| CONCLUSION