Effect of incorporating p-type hydrogenated nanocrystalline silicon buffer layer on amorphous silicon n–i–p solar cell performances

This paper reports on the impact of inserting a p-type hydrogenated nanocrystalline silicon (p-nc-Si:H) buffer layer on the performances of amorphous a-Si:H based component solar cells, with no back reflector. Using a one dimensional simulation program, performances of n–i–p and n–i–p′–p structures are evaluated and compared to recent experimental results. A good agreement is obtained and a set of parameters, characterizing the layers constituting the structures, is extracted. The modeling showed an improvement of the cell's external parameters, when incorporating a p′-nc-Si:H buffer layer at the i/p interface. This result is mainly due to the reduction of the density of defect states at the i/p interface. The presence of the buffer layer accommodates the band offsets at the p–i heterojunction, reduces the electric field, the trapped hole density and the recombination rate at the i/p interface. The buffer layer also causes an enhancement in the short wavelength response, corresponding to the visible spectrum. Consequently, an improvement of the cell efficiency from 6.32% for the bufferless cell to 7.40% for the cell with buffer layer is registered.

► n–i–p and n–i–p’–p structures are simulated and compared to experimental results.
► The devices are amorphous and nanocrystalline silicon based solar cells.
► A set of parameters, characterizing the layers of each structure, is extracted.
► Incorporating a p’ layer at the i/p interface improved the cell’s performances.
► The p’ buffer reduces the band offsets and the density of defect at the interface.