Quasi-intrinsic absorber engineering for electric-field-driven carrier collection in CdIn₂Se₄ solar cells

Field-limited carrier collection remains a key challenge in thin-film solar cells employing wide-bandgap and low-mobility absorber materials. In this work, a Cu₂O/CdIn₂Se₄/TiO₂ solar cell is numerically investigated to mitigate this limitation through electric-field engineering using a p-i-n device configuration . CdIn₂Se₄ is employed as the absorber layer and is modeled under compensated quasi-intrinsic conditions (N D ≈ N A ) to realize a near-intrinsic absorber region within the p-i-n device architecture. This configuration extends the internal electric field throughout the absorber layer, thereby enhancing charge separation, suppressing bulk recombination, and improving carrier collection efficiency. The optimized device consists of p-type Cu₂O, quasi-intrinsic CdIn₂Se₄, and n-type TiO₂, with carefully selected material parameters including bandgap, electron affinity, carrier mobility, and dielectric permittivity. Under optimized and practically realizable conditions using a compensated quasi-intrinsic absorber (N A ≈ N D = 5.91 × 10¹⁵ cm⁻³), the device achieves an open-circuit voltage of 1.31 V, a short-circuit current density of 19.16 mA cm⁻², a fill factor of 86.66%, and a power conversion efficiency of 21.91%. Comparative energy-band, electric-field, and recombination analyses between p-i-n, p-type, and n-type absorber configurations reveal that the p-i-n structure produces a wider depletion region and an extended electric field across the absorber, resulting in significantly reduced recombination and enhanced carrier extraction. Although higher numerical efficiencies (up to 30.2%) can be simulated at extreme doping levels (10²³ cm⁻³), such conditions are physically unattainable in CdIn₂Se₄ and are therefore discussed only to illustrate theoretical performance trends. The effects of bulk defect density, acceptor and donor concentrations, operating temperature, series and shunt resistances, and quantum efficiency are systematically examined to understand the electric-field-assisted carrier collection mechanism. The results indicate that low defect density, optimized compensated doping, and minimized resistive losses are essential for achieving high photovoltaic performance. This study provides important design insights into electric-field-assisted carrier collection strategies for improving CdIn₂Se₄-based solar cells.