In this project, a new type of InP solar cell was investigated. The main idea is that light is converted to electrical current in p-i-n photodiodes formed in thin InP semiconductor nanowires epitaxially grown on an InP substrate. Two different types of samples were investigated. In the first sample type (series C03), the substrate was used as a common p-type electrode, whereas a short p-segment was included in all nanowires for the second sample type (B07). Current – voltage (I-V) characteristics with and without illumination were measured, as well as spectrally resolved photocurrents with and without bias. The main conclusion is that the p-i-n devices showed good rectifying behavior with an onset in photocurrent that agrees with the corresponding energy band gap of InP. An interesting observation was that in series B07 (with included p-segments) the photocurrent was determined by the band gap of hexagonal Wurtzite crystal structure, whereas series C03 (without p-segments) displayed a photocurrent dominated by the InP substrate which has a Zincblende crystal structure. We found that the overall short-circuit current was ten as large for the latter sample, stressing the importance of the substrate as a source of photocurrent.