TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The solar cell further comprises: an electrostatic field between each of the structural imperfections and the p-type group III-nitride alloy for separating the photoexcited electron-hole pairs and accumulating electrons around the structural imperfections in the first area possessing a first composition of the p-type group III-nitride alloy having its conduction band edge beneath the EFs; a first electrical contact coupled to the p-type group III-nitride alloy layer, a silicon base substrate, and a second electrical contact coupled to the silicon base substrate; and at least one buffer layer formed between the silicon base substrate and the n-type group III-nitride alloy layer. The compositional grading of the p-type group III-nitride alloy creates a potential that drives the electrons accumulating around the structural imperfections to the layer of n-type group III-nitride alloy for collection. The charge separation of the photoexcited electron-hole pairs is performed separately from collection of the electrons at the n-type group III-nitride alloy. The group III-nitride alloy layer is of formula (InxGa1-xN) or (InyAl1-yN), where the first composition of the p-type group III-nitride alloy having its conduction band edge beneath the EFs is of formula (InzGa1-zN) or (Inz1Al1-z1N), and the second composition of the p-type group III-nitride alloy having its conduction band edge above the EFs is of formula (InmGa1-mN) or (InnAl1-nN). The group III-nitride alloy layer comprises an alloy of formula (InxAlyGa1-x-yN). The structural imperfections comprise at least one of threading dislocations, grain boundaries, and/or columns in the p-type group III-nitride alloy. The structural imperfections are n-type conductors in the first area possessing a first composition of the p-type group III-nitride alloy having its conduction band edge beneath the Fermi level stabilization energy (EFs), to transport the accumulated photoexcited electrons to the layer of n-type group III-nitride alloy. The p-type group III-nitride alloy layer and the n-type group III-nitride alloy layer form a top cell in the solar cell for absorbing a first portion of the solar spectrum, where the silicon base substrate is formed to possess a p-type region and an n-type region so as to form a bottom p-n junction cell in the solar cell for absorbing a second portion of the solar spectrum.x, y = 0-1;z = 0.35-1;m = less than 0.35;z1 = 0.57-1; andn = less than 0.57.