Towards 12% stabilised efficiency in single junction polymorphous silicon solar cells: experimental developments and model predictions

Sergey Abolmasov,Pere Roca I Cabarrocas,Parsathi Chatterjee

doi:10.1051/epjpv/2015011

Abstract

We have combined recent experimental developments in our laboratory with modelling to devise ways of maximising the stabilised efficiency of hydrogenated amorphous silicon (a-Si:H) PIN solar cells. The cells were fabricated using the conventional plasma enhanced chemical vapour deposition (PECVD) technique at various temperatures, pressures and gas flow ratios. A detailed electrical-optical simulator was used to examine the effect of using wide band gap P-and N-doped μ c-SiOx :H layers, as well as a MgF2 anti-reflection coating (ARC) on cell performance. We find that with the best quality a-Si:H so far produced in our laboratory and optimised deposition parameters for the corresponding solar cell, we could not attain a 10% stabilised efficiency due to the high stabilised defect density of a-Si:H, although this landmark has been achieved in some laboratories. On the other hand, a close cousin of a-Si:H, hydrogenated polymorphous silicon (pm-Si:H), a nano-structured silicon thin film produced by PECVD under conditions close to powder formation, has been developed in our laboratory. This material has been shown to have a lower initial and stabilised defect density as well as higher hole mobility than a-Si:H. Modelling indicates that it is possible to attain stabilised efficiencies of 12% when pm-Si:H is incorporated in a solar cell, deposited in a NIP configuration to reduce the P/I interface defects and combined with P- and N-doped μ c-SiOx :H layers and a MgF2 ARC.

Highlights

To this end, we have been experimenting with an amorphous silicon (a-Si):H-like material: hydrogenated polymorphous silicon, which is produced by the standard RF glow discharge decomposition of silane highly diluted in hydrogen, under conditions close to powder formation [4,5,6,7,8]
The reason for using the P-μc-Si:H/P-a-SiC:H design is given in detail in reference [13] and for using the P-μc-Si:H/P-μcSiOx:H window structure described in the introductory section
For polymorphous silicon (pm-Si):H solar cells deposited in PIN and NIP configurations in our laboratory [19], it has been found that cells deposited in the latter configuration degrade much less – from an initial efficiency of ∼9.3% to about 8.2%; while those deposited in the PIN configuration degrade from a lower initial efficiency of ∼8.5% to 5.8%, or even down to 3%, in the worst cases after 500 h of light-soaking

Summary

Introduction

We have been experimenting with an a-Si:H-like material: hydrogenated polymorphous silicon (pm-Si:H), which is produced by the standard RF glow discharge decomposition of silane highly diluted in hydrogen, under conditions close to powder formation [4,5,6,7,8]. Pm-Si:H is a nano-structured silicon material with medium range order which shows up in the superior hole transport properties as deduced from diffusion induced time resolved microwave conductivity [8] and time-of-flight measurements [9]. It exhibits lower initial [5] and stabilised defect densities than standard a-Si:H [1, 9, 10], with the ημτ product of electrons 200– 700 times higher than that of standard a-Si:H for samples in the as-deposited state [1], and attaining values after light-soaking comparable to those of standard a-Si:H films before degradation [1,4,5,6,7].

Objectives

Methods

Results

Conclusion