Roles of polarization effects in InGaN/GaN solar cells and comparison of p-i-n and n-i-p structures.

ABSTRACT

The p-i-n and n-i-p InGaN/GaN solar cells (SCs) with Ga-face and N-face under different Indium composition were investigated and compared. From the charge distribution analysis, it can be deduced that if p-i-n was converted to n-i-p and the polarity of the SC was reversed simultaneously, or vice versa, the role of polarization effect (i.e. whether hinder or facilitate the photon-generated carriers transport) for the two SC structures would be resembling, though they had difference in degrees. The SC performance, energy band diagram at zero bias condition, recombination rate distribution and carrier concentration distribution of these SCs were analyzed, which suggested that although the polarization effect could facilitate the carrier transport both in p-i-n N-face SC and n-i-p Ga-face SC, the p-i-n N-face SC was apt to have better performance more or less if the barrier induced by band-offset at the hetero-interface would not block the carrier transport dominantly, e.g. when Indium content was less than or equal to 0.3. Besides, the high Indium content would result in the high band-offset barrier, and the barrier would affect the carrier transport in two ways, one was to hamper the carrier transport directly, and the other was to influence the electric field in i-region indirectly.