Investigation Of Properties Of A Vertical-Type InGaN Solar Cell And Improved Photoelectric Performance

In order to optimize InGaN solar cell (SC) structures and effectively guide the preparation, the properties of the vertical-type InGaN SC have been investigated and through inhibiting negative impact of polarization effect on InGaN SC to improve SC’s performance, this paper carried out a series of researches.1、Through APSYS simulation software, the performances of the p-i-n and n-i-p SC structures with graded In composition have been compared. It is found that the n-i-p structures don’t have obvious advantage in the device performance over the p-i-n ones when In composition of the i-InGaN layer is low, which yet presents better performance with higher In composition. When In composition is 0.62, the SC conversion efficiency reaches 8.48%. The further analysis indicates that the polarization electric field in the InGaN layer has the same directions with the built-in one in the depletion region for the case of n-i-p SC structures, which is very beneficial for carrier transport. The n-i-p SC structures with graded In composition are proven to be beneficial for high performance InGaN SCs. And through APSYS simulation software, the vertical structure of the InGaN solar cell performance are studied. The results found that the short circuit current of vertical-type InGaN SC got obvious improvement.2、The properties of Ga-polar InGaN SC and N-polar InGaN SC with graded In composition have been investigated. Through APSYS simulation software, the performances of structure A, structure B, structure C and structure D have been compared. The structure A is p-i-n device without any grading in intrinsic layer; Structure B consists of i-InxGai-xN graded layer with variation of In composition from 0 to x in intrinsic layer from bottom to top; The In composition of structure C from x to 0, respectively, In composition of structure D from 0 to x and x to 0. It is found that structure B have best performance on Ga-face, and when In composition is 0.17, the SC conversion efficiency reaches 2.18%; Structure A have best performance on N-face, and when In composition is 0.62, the SC conversion efficiency reaches 9.28%. The further analysis indicates that grading layer weaken polarization electric field in the depletion region on Ga-face; Structure B have best performance on Ga-face because it can absorb more low energy photons when the side with high In composition is close to light incident surface. Meanwhile, polarization electric field has the same directions with the built-in one in the depletion region on N-face. Grading layer lead to the decrease of short circuit current, which is harmful to improve the efficiency of SC.3、Through technology of MOCVD epitaxy growth and epitaxial wafer wet etching、deposition of medium、grinding and polishing, preparation method for low-dislocation density AlxGai-xN epitaxial thin film was present. The method mainly includes the following steps: MOCVD epitaxy growth of AIN template; Growth of inserted layer with AlGaN/AIN superlattice; Growth of AlGaN layer; Wet etching AlGaN to form the dislocation pits (including screw type, edge dislocation, and mixed dislocations); Deposition dielectric film (SiNx,、SiO2、Al2O3、etc.) cover the epitaxial wafer surface, medium filling in dislocation pits, blocking dislocation extended upward; Grinding and polishing epitaxial wafer to get rid of the dielectric film except dislocation pit area, uncover AlGaN layer; Secondary MOCVD epitaxy growth of AlGaN layer, we get AlGaN epitaxial material with low-dislocation density and smooth surface.