Model for a-Si:H/c-Si interface recombination based on the amphoteric nature of silicon dangling bonds

Abstract

The performance of many silicon devices is limited by electronic recombination losses at the crystalline silicon ͑c-Si͒ surface. A proper surface passivation scheme is needed to allow minimizing these losses. The surface passivation properties of amorphous hydrogenated silicon ͑a-Si:H͒ on monocrystalline Si wafers are investigated here. We introduce a simple model for the description of the surface recombination mechanism based on recombination through amphoteric defects, i.e. dangling bonds, already established for bulk a-Si:H. In this model, the injection-dependent recombination at the a-Si:H/c-Si interface is governed by the density and the average state of charge of the amphoteric recombination centers. We show that with our surface recombination model, we can discriminate between the respective contribution of the two main mechanisms leading to improved surface passivation, which is achieved by ͑a͒ the minimization of the density of recombination centers and ͑b͒ the strong reduction of the density of one carrier type near the interface by field effect. We can thereafter reproduce the behaviors experimentally observed for the dependence of the surface recombination on the injection level on different wafers, i.e., of both p and n doping type as well as intrinsic. Finally, we are able to exploit the good surface passivation properties of our a-Si:H layers by fabricating flat heterojunction solar cells with open-circuit voltages exceeding 700 mV.

Light-induced performance increase of silicon heterojunction solar cells

“…Figure 3 shows s eff curves as a function of the carrier injection level, Dn, during LS of the symmetric i-p/i-p and i-n/i-n structures. Calculated s eff curves, based on an a-Si:H/ c-Si interface recombination model, 38 were fitted to these measurements. The formalism used for these calculations has two model parameters, namely, the interface state density, N s , and the interface charge density, Q s .…”

“…The interface states are considered to be silicon dangling bonds, which are amphoteric, with associated capture cross sections for electrons and holes (r n þ and r p À for the charged states, and r n 0 and r p 0 for the neutral states, respectively; see also Ref. 38). The capture cross section ratios were taken to be r n 0 /r p 0 ¼ 1/ 20 and r n þ /r n 0 ¼ r p À /r p 0 ¼ 500, following Olibet et al 38 Figure 3 shows that the experimental LS data can be fitted well by the employed calculations.…”

“…38). The capture cross section ratios were taken to be r n 0 /r p 0 ¼ 1/ 20 and r n þ /r n 0 ¼ r p À /r p 0 ¼ 500, following Olibet et al 38 Figure 3 shows that the experimental LS data can be fitted well by the employed calculations. The uppermost solid curve represents the maximum bulk lifetime based on the Auger recombination parameterization by Richter et al 39 From the fitting results it follows that the light-induced changes in s eff of i-p/i-p structures are mainly driven by a decreasing N s value (without much of a change in Q s ); for the i-n/i-n structures, both parameters N s and Q s are seen to change over LS.…”

Capacitance–voltage spectroscopy and analysis of dielectric intrinsic amorphous silicon thin films

“…ND reference values were calculated using the Olibet model [15]. The model itself is based on the effective nlinority can·ier lifetime ( TeffJ measurements [15].…”

“…ND reference values were calculated using the Olibet model [15]. The model itself is based on the effective nlinority can·ier lifetime ( TeffJ measurements [15]. Related measmements were performed using a WCT 120 lifetime tester from Sinton Instruments [16].…”