The effects of pulse repetition rate on the structural, optical, and electrical properties of CIGS films grown by pulsed laser deposition

Abstract

Well crystallized CuIn1−xGaxSe2 (CIGS, x=0.22–0.26) films were deposited at the temperatures below 300°C by pulsed laser deposition. Increasing pulse repetition rate from 5Hz to 1kHz significantly increased the crystallinity of films. All the films were Cu rich and those deposited with 5Hz showed higher Ga deficiency, but in those deposited with 1kHz the loss of Se was higher. The growth mechanisms under the low and high repetition rates as well as their effects on the grain size and composition were discussed in detail. All the films had p-type conductivity. The resistivity of 1kHz films was two times higher but the carrier concentration was four times lower than the 5Hz films. I–V characteristics were measured on the n-ZnO/p-CIGS heterojunctions. The junction made with 1kHz film had a single ideality factor of 1.3 up to the high current limit, which is often seen in the high efficiency CIGS solar cells, whereas the I–V curve of the junction made with 5Hz film consisted of two sections described by large ideality factors of 3.0 and 4.8, respectively, indicating that there are two recombination mechanisms each of which dominates at a different current region.