Computer simulation model of the effects of interface states on high-performance amorphous silicon solar cells

Abstract

A computer simulation model of amorphous silicon solar cells using a Scharfetter and Gummel solution of Poisson’s equation and Taylor and Simmons occupancy statistics for the dangling bond gap states (D states), has been developed. With a suitable choice of parameters, the numerical results for solar cell collection efficiency and dark and illuminated I-V characteristics agree well with experimental values. The model has been used specifically to study the influence of interface states at the TCO-p (transparent conductive oxide), p-i, i-n, and n-metal interfaces and to explain the beneficial role of a graded-band-gap layer at the p-i interface.

Improvement of amorphous silicon n-i-p solar cells by incorporating double-layer hydrogenated nanocrystalline silicon structure

“…Due to the compositional disorder and morphological fluctuation at the i/p interface, a large amount of dangling bonds may exist and act as recombination centers or deep trapping centers [1]. Tasaki et al reported that the interface states cause abrupt band bending at the i/p interface and reduce the electric field in the i layer, consequently, the recombination rate near this interface region increases significantly [2]. For the purpose of improving the i/p interfaces of the a-Si:H solar cells, some methods have been developed including the application of a buffer layer inserted between the i-and p-layers.…”

Ultrathin boron-doped microcrystalline silicon as a novel constant band gap buffer inserted at the p-a -SiC:H/ i-a -Si:H interface of amorphous silicon solar cells

“…In case of the buffered cell with a 50 Å p/i interface section ͓Fig. 9͑b͔͒, the J sc is improved with increasing the N A of the buffer from 1ϫ10 18 cm Ϫ3 to 1ϫ10 19 cm Ϫ3 . Such an enhancement is caused by the stronger electric field due to higher N A .…”

“…12. When the N A in the buffer is lower than the doping level of the pa-SiC:H (5ϫ10 18 cm Ϫ3 ), the buffer gives negative effects on the cell performance due to a lower electric field, resulting in the poorer V oc and FF than those of the bufferless cell. In case of the buffered cell with a 50 Å p/i interface section ͓Fig.…”

“…18 They postulated three assumption to clarify the improvement of the V oc and the short wavelength response through the insertion of a-SiC:H buffer which is founded experimentally. First assumption is that the buffer has a band structure with linear grading profiles from 2.0 eV in the p-a-SiC:H to 1.72 eV in the a-Si:H. The grading band gap profiling causes an electric field at the p/i interface region to be stronger and thereby photogenerated electron-hole pairs are swifted faster to the p-a-SiC:H and i-a-Si:H layer, respectively, before recombining each other.…”

Two-dimensional modelling and simulation of hydrogenated amorphous silicon p+–n–n+ solar cell

“…Further more, in the case of p + -n-n + cell, the n-doping profiling in the absorber layer helps to get abrupt p + -n junction for high open circuit voltage. Since the carrier collection in the cell through p + layer with illumination is limited by electron transport than hole transport [32] and since the fill factor and the efficiency of the p-i-n cell are limited by the p/i interface recombination loss [33], the intentional n-doping in the absorber layer of a-Si:H based solar cell may have a critical role in determining the cell performance. However, dependence of doping concentration in the absorber layer on the photo parameters of the solar cell must be investigated in order to optimize the performance.…”