Light absorption and emission in photovoltaic devices

Abstract

Historically, light absorption and emission has long been of broad interest in photovoltaic research, where these processes have been not only optimized for a high conversion efficiency but investigated to develop reliable optical characterization techniques. Although various aspects are being perfected, some issues remain unsolved due to their complexity; new technical issues also arise as solar cell technology evolves, where rapid adjustment is required to keep pace with the development.This thesis covers multiple topics relevant to the field, contributing to both the physics and characterization of solar cells. First, as a complement to Shockley’s p-n junction diode theory, an investigation of optoelectronic transport in arbitrary three-dimensional solar cell geometries shows that the ideal solar cell equation retains its traditional form in the presence of photon recycling, which however improves the dark saturation and light-generated currents. Then, taking note of developments over recent years, the applicability of spectral response analysis is reassessed as a means of determining cell optical and electrical properties, giving rise not only to extended applicability to front surface field cells, but new blue response and simplified infrared response analyses. After that, increased insights into band luminescence imaging of operational devices are provided through analytic study. With the dependence clearly illustrated, the present analytical approach not only simplifies results when local spatial uniformity is assumed, but allows more insights into the impact of lateral carrier injection as an operational feature increasingly evident in high efficiency solar cells. Finally, radiative coupling between the cells in tandem stacks is investigated as an increasingly important factor for tandem devices where energy conversion efficiency now exceeds 46%. The investigation not only extends earlier coupling models to account for both electroluminescent and photoluminescent coupling components, but provides more general insight into the impact on device performance and demonstrates an equivalent circuit approach as an efficient means of clarifying the complex interactions involved