[Paper Review] Silicon solar cells efficiency analysis. Doping type and level optimization

А. В. Саченко, V. P. Kostylyov+6 more|arXiv (Cornell University)|Jun 9, 2015

Silicon and Solar Cell Technologies8 references3 citations

TL;DR

This paper analyzes the efficiency of silicon solar cells with n-type and p-type bases, focusing on doping type and level optimization under Fe-related Shockley-Read-Hall recombination. It demonstrates that n-type cells benefit from increased doping due to asymmetric recombination parameters, while p-type cells degrade under the same conditions, with experimental HIT cell data confirming theoretical predictions through precise matching of surface recombination velocity and series resistance.

ABSTRACT

The theoretical analysis of photovoltaic conversion efficiency of highly effective silicon solar cells (SC) is performed for n-type and p-type bases. The case is considered when the Shockley-Read-Hall recombination in the silicon bulk is determined by the deep level of Fe. It is shown that due to the asymmetry of the recombination parameters of this level the photovoltaic conversion efficiency is increasing in the SC with the n-type base and decreasing in the SC with the p-type base with the increase in doping. Two approximations for the band-to-band Auger recombination lifetime dependence on the base doping level are considered when performing the analysis. The experimental results are presented for the key characteristics of the solar cells based on $α-Si:H-n-Si$ heterojunctions with intrinsic thin layer (HIT). A comparison between the experimental and calculated values of the HIT cells characteristics is made. The surface recombination velocity and series resistance are determined from it with a complete coincidence of the experimental and calculated SC parameters' values.

Motivation & Objective

• To investigate the impact of doping type (n-type vs. p-type) and level on photovoltaic efficiency in silicon solar cells.
• To analyze the role of Fe-related deep-level recombination (Shockley-Read-Hall) in determining efficiency differences between n-type and p-type bases.
• To optimize doping levels by modeling band-to-band Auger recombination dependence on doping concentration using two approximations.
• To validate theoretical predictions against experimental data from α-Si:H/i-n-Si heterojunction solar cells (HIT structure).
• To extract and match key device parameters—surface recombination velocity and series resistance—between experiment and simulation.

Proposed method

• Theoretical modeling of photovoltaic efficiency using Shockley-Read-Hall recombination with Fe as the dominant deep level.
• Application of two distinct approximations for the dependence of band-to-band Auger recombination lifetime on base doping concentration.
• Simulation of solar cell performance for both n-type and p-type silicon bases under identical recombination and doping conditions.
• Comparison of calculated open-circuit voltage, short-circuit current, and fill factor with experimental data from α-Si:H/i-n-Si heterojunction solar cells.
• Parameter extraction of surface recombination velocity and series resistance via fitting theoretical curves to experimental I-V characteristics.
• Use of the complete coincidence between experimental and calculated parameters as a validation criterion for the model.

Experimental results

Research questions

• RQ1 How does the doping type (n-type vs. p-type) influence photovoltaic efficiency when Fe-related Shockley-Read-Hall recombination dominates?
• RQ2 Why does increasing doping improve efficiency in n-type cells but degrade it in p-type cells under the same recombination conditions?
• RQ3 How do different approximations for Auger recombination lifetime affect the predicted efficiency trends with doping level?
• RQ4 To what extent can theoretical models reproduce experimental characteristics of HIT solar cells with intrinsic amorphous silicon layers?
• RQ5 What are the values of surface recombination velocity and series resistance that yield full agreement between theory and experiment in HIT cells?

Key findings

• The asymmetry in recombination parameters of Fe-related deep levels causes n-type silicon solar cells to exhibit increased efficiency with higher doping, while p-type cells show decreased efficiency.
• Theoretical predictions for n-type cells closely match experimental data from α-Si:H/i-n-Si heterojunction solar cells, confirming model validity.
• The surface recombination velocity and series resistance values extracted from experimental I-V curves are fully consistent with those used in the theoretical simulations.
• The two approximations for Auger recombination lifetime yield similar qualitative trends, supporting the robustness of the efficiency analysis.
• The complete agreement between calculated and measured solar cell parameters (Voc, Isc, FF) validates the model’s accuracy in predicting device performance.
• The study confirms that n-type silicon is more favorable than p-type for high-efficiency solar cells when Fe contamination is present and doping is optimized.