  Bifacial tandem cells promise to reduce three fundamental losses
(above-bandgap, below bandgap, and the uncollected light between panels)
inherent in classical single junction PV systems. The successive filtering of
light through the bandgap cascade, and requirement of current continuity make
optimization of tandem cells difficult, accessible only to numerical solution
through computer modeling. The challenge is even more complicated for bifacial
design. In this paper, we use an elegantly simple Markov chain approach to show
that the essential physics of optimization is intuitively obvious, and deeply
insightful results can obtained analytically with a few lines of algebra. This
powerful approach reproduces, as special cases, all the known results of
traditional/bifacial tandem cells, and highlights the asymptotic efficiency
gain of these technologies.
