Doping with phosphorus reduces anion vacancy disorder in CdSeTe semiconductors enabling higher solar cell efficiency

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Doping in pn junction devices, like polycrystalline solar cells, typically enhances junction fields for charge carrier collection, mitigating recombination losses.
• Alloying cadmium telluride (CdTe) with selenium (Se) to form CdSeTe reduces recombination but introduces complex defect states that limit efficiency via charge carrier trapping and trap-limited mobility.

Purpose of the Study:

• To investigate the effect of doping on charge carrier trapping and electronic band tails in inorganic solar cells.
• To explore phosphorus (P) doping in CdSeTe solar cells to reduce defect states and improve photovoltaic performance.

Main Methods:

• Alloying CdTe with Se to create CdSeTe semiconductor material.
• Doping CdSeTe with phosphorus (P), nitrogen (N), arsenic (As), and antimony (Sb).
• Characterization of electronic band tails (Urbach energies) and charge carrier trapping.
• Measurement of ambipolar mobilities, fill factor, and power conversion efficiencies.
• Device performance simulations to analyze defect reduction impacts.

Main Results:

• Phosphorus doping of CdSeTe significantly reduced electronic band tails (Urbach energies).
• P-doping lessened the impact of near-valence band trap states.
• Ambipolar mobilities improved to over 50 cm²V^-1s^-1.
• Fill factor increased from 76% to 79%.
• Device efficiencies saw an absolute increase of 0.9%.

Conclusions:

• Phosphorus doping is an effective strategy to reduce charge carrier trapping and electronic band tails in CdSeTe inorganic solar cells.
• Defect reduction through P-doping leads to improved photovoltaic performance, including higher fill factors and efficiencies.
• Simulations confirm that defect reduction enhances device performance, particularly in the radiative limit.