Measuring the Absorber Doping Concentration of Si, CdSeTe, and Perovskite Solar Cells Using Injection-Dependent Quasi-Steady-State Photoluminescence

There are few doping concentration measurement techniques that are contactless and usable for all semiconductors. In this article, we demonstrate the use of injection-dependent quasi-steady-state photoluminescence to simultaneously measure the external radiative efficiency, minority-carrier lifetime, and activated dopant concentration of solar cell absorber layers. We first demonstrate this measurement on Si, for which established lifetime and doping measurement techniques exist, and determine a doping density of 4.2 × 10¹⁵ cm⁻³, which is within a factor of 2 from the 2.1 × 10¹⁵ cm⁻³ value calculated from quasi-steady state photoconductance. Then, we demonstrate the use of the technique to measure doping concentrations of CdSeTe over two orders of magnitude and of perovskite down to nearly 10¹⁴ cm⁻³—materials that are much more difficult to accurately assess with other techniques.

I. Introduction

Knowledge of the doping concentration N_D is useful for the fabrication of solar cells and other semiconductor-based devices [1], [2], [3]. N_D can affect the minority-carrier lifetime, electrical conductivity, and optical absorption coefficients of a material [3], [4], [5]. N_D is often determined by measuring the free-electron concentration n₀, which allows for the measurement of “unintentional doping” (i.e., n₀ in materials that are not substitutionally doped) in addition to substitutional doping [6], [7].