2.1 - 2.2 eV top cells are an essential and challenging part of future high-efficiency multi-junction solar cells. In this work, we report 2.1 and 2.2 eV AlGaInP solar cells grown by molecular beam epitaxy (MBE) on GaAs. As-grown cells exhibit strong trap-assisted recombination, resulting in high bandgap-voltage offset (WOC) values and compromised carrier collection. Bringing the space charge region of the solar cell closer to the front surface by eliminating extra thickness improves carrier collection due to short minority carrier diffusion length. Another consequence of insufficient diffusion length is that field-assisted carrier collection (FACC) significantly degrades the fill factor of the AlGaInP solar cells presented here. Rapid thermal annealing (RTA) leads to increased photoluminescence intensity and shows the potential for improved cell performance.