Slightly better discussion links:

http://news.columbia.edu/content/Columbia-Chemists-Find-Key-...

http://science.sciencemag.org/content/353/6306/1365.full

TLDR;

HOIPs could lead to a doubling in solar cell efficiency [to 50%]

(Yes, you find the most tangible quote is actually in an image)

Apart from that they speak of lower costs without any numbers attached.

How can an article talk about more efficient solar cells and not even mention in passing technology already available such as triple junction gallium arsenide?

I mean the mars rovers are using 30+% efficient cells NOW. The cost are much higher than silicon, but this is working producible technology that we just need to figure out how to lower costs of.