Determination of minority carrier diffusion length and back-surface recombination velocity in thin-film solar cells using lateral photocurrent

Abstract

Accurate determination of the minority carrier diffusion length (Ld) and back-surface recombination velocity (Sb) is essential for understanding carrier transport and recombination in thin-film solar cells, yet remains challenging due to the concurrent effects of drift–diffusion transport and multiple recombination pathways. In this work, we present a method to extract Ld and Sb from wavelength-dependent lateral photocurrent measurements. The approach exploits the anisotropy of carrier transport in bandgap-graded absorbers, where the quasi-electric field is predominantly oriented along the thickness direction, resulting in diffusion-dominated lateral transport. By relating the lateral collection length to an effective diffusional collection length through two limiting cases, bounded estimates of Ld and Sb are obtained without requiring explicit knowledge of the bandgap profile. The method is applied to a Cu(In,Ga)Se2 thin-film solar cell, yielding Ld ≈ 1.8 μm and Sb in the range of 5.3 × 104–1.2 × 105 cm/s, consistent with reported values. The proposed framework provides a physically motivated approach to separate transport and recombination contributions using experimentally accessible quantities and is applicable to both graded and ungraded absorber systems.