  Here we present the experimental results of an inverted three-terminal
heterojunction bipolar transistor solar cell (HBTSC) made of GaInP/GaAs. The
inverted growth and processing enable contacting the intermediate layer (base)
from the bottom, which improves the cell performance by reducing shadow factor
and series resistance at the same time. With this prototype we show that an
inverted processing of a three-terminal solar cell is feasible and pave the way
for the application of epitaxial lift-off, substrate reuse and mechanical
stacking to the HBTSC which can eventually lead to a low-cost high-efficiency
III-V-on-Si HBTSC technology.
