Perovskite Tandem Solar Cell Passivation & Efficiency Workbench

Interfacial Molecular Salt Layer NANOMETER REGIME

Salt Layer Thickness (d) 1.2 nm

0 nm = raw unpassivated traps. Optimal tunnel thickness is ~1.0–1.4 nm; >2.5 nm induces series resistance tunneling barrier.

Molecular Dipole Shift (ΔV_dipole) 0.18 V

Molecular salt terminal cation/anion dipole aligns conduction bands, creating an electron-selective field and minimizing interface recombination.

Trap State Density (N_t) 2.5 × 10¹⁰ cm⁻²

Surface defect density governing Shockley-Read-Hall non-radiative recombination velocity S_r.

Tandem Sub-Cell Bandgap Matching AM1.5G COUPLING

Top Perovskite Bandgap (E_g1) 1.68 eV

Wide bandgap top cell absorbs UV/Vis photons (350–750 nm), transmitting NIR photons to the bottom cell.

Bottom Silicon Bandgap (E_g2) 1.12 eV

Crystalline silicon bottom absorber fixed at standard E_g = 1.12 eV (absorbing 750–1100 nm).

Recombination Velocity (S_r) 142 cm/s

Reduced from >12,000 cm/s in unpassivated films to <200 cm/s with nanometer molecular salt fix.

Tandem Total PCE (η)

29.02%

Target 29% Unlocked!

Tandem V_oc

1.942V

Top: 1.25V | Bot: 0.69V

Matched J_sc

19.45mA/cm²

2-Terminal Series Limit

Fill Factor (FF)

82.1%

R_s: 0.42 Ω·cm²

Tandem J-V Curve & Max Power Point (MPP) P_max: 290.2 W/m²

AM1.5G Spectral Photon Split & Subcell EQE Current matched: Δ0.12 mA

Interfacial Band Energy Alignment & Trap Passivation ΔE_c: 0.04 eV (Favorable Extraction)

Physics Breakdown: Why Nanometer Salt Passivation Reaches 29% PCE

Standard 3D perovskite surfaces exhibit uncoordinated Pb²⁺ and halide vacancies that act as deep Shockley-Read-Hall non-radiative recombination centers, limiting Voc to <1.15V. Applying an ultrathin (~1.2 nm) molecular salt layer creates a molecular dipole that eliminates uncoordinated dangling bonds and induces favorable band bending, driving recombination velocity below 150 cm/s while preserving low series tunneling resistance.

Shockley-Read-Hall Kinetics U_SRH ∝ N_t · v_th · σ. Passivation reduces trap density N_t by >95%, boosting sub-cell Voc by +110 mV.

Tunneling vs Series Resistance Excess thickness (>2.5 nm) creates a classical tunneling barrier, causing fill factor FF to collapse rapidly from 82% to <65%.

2-Terminal Tandem Current Matching Total short-circuit current J_sc is constrained by min(J_sc,top, J_sc,bot). Peak efficiency requires optimal bandgap split ~1.68 eV / 1.12 eV.