Rear interface point contact passivation of Cu(In,Ga)Se2 thin film solar cells by Al2O3 nanoparticles

To form a rear interface point contact passivation structure for Cu(In,Ga)Se₂ (CIGS) thin-film solar cells, Al₂O₃ nanoparticles with different coverage were fabricated at the interface between CIGS and Mo film by low-cost solution method, and the passivation mechanism was investigated systematically. Based on a series of tests, the device performance improvement mainly came from the increase of short circuit current density (J_SC), resulting from the reflection enhancement by Al₂O₃ particles at the CIGS/Mo interface, which promotes the light absorption by CIGS film. In addition, the effect on the three-step co-evaporation process led to a red shift in the absorption limit, thereby increasing the quantum efficiency. Further, Al₂O₃ particles buried at the rear interface exhibited more negative potential than the uncovered locations, which inhibits the diffusion of minority carriers toward the rear interface and decreases the recombination of carriers. In summary, the local passivation near the rear interface brings an absolute efficiency increase of 0.75 % over the average efficiency of the reference cell, and a 17.76 % efficient solar cell was fabricated with an optimal coverage of Al₂O₃ particles.