Optoelectronic properties of organic-inorganic halide perovskites are exceptional with solar cells showing efficiency comparable with conventional photovoltaic technologies. However, with issues of material stability and toxicity of Pb, it is important to understand if Pb can be replaced while maintaining the high power conversion efficiencies of (FA,MA,Cs)Pb(I,Br) 3. Herein, practical efficiency limits of Pb and Pb-free perovskite absorbers are analyzed using a 1D simulator for n-i-p or p-in device structures. SCAPS-1D baseline models for perovskite absorber materials with and without Pb are developed to numerically reproduce the experimental current density-voltage (JV) and external quantum efficiency (EQE) of champion devices from literature. From these baseline models, the efficiency limits are determined based on optimizing the interface band alignments, reduction in midgap defect density, increased absorption coefficient, and no parasitic losses. SCAPS-1D simulations suggest that 1) theoretically determined efficiency limit of Cs 2 PtI 6 perovskites is comparable with (FA,MA,Cs)Pb(I,Br) 3 perovskites, 2) FA 4 GeSbCl 12 is a promising photoabsorber; and 3) for efficient photoconversion with Sn-, Ge-, Ti-, or Ag-based compounds, a reduction of defect density and increase in absorption coefficient is needed.

The effects of Na and RbF alkali treatment on the metastability behavior of CdS/Cu(In,Ga)Se2 solar cells are investigated with stress factors of heat, junction bias, and illumination. Four device types with and without Na or RbF treatments are subjected to heat‐ and light‐soaking under open‐ and short‐circuit (OC, SC) junction bias. Low‐Na devices show a higher bandgap due to increased minimum Ga content, higher recombination current, and lower open‐circuit voltage (VOC). Devices with RbF post‐deposition treatment (PDT) show an improvement in net doping density ≈1016 cm−3, VOC, and efficiency. Heat‐ and light‐soaking under OC junction bias provokes an increase in net carrier concentration and VOC irrespective of the alkali treatments. After SC stress, a decrease in VOC and net carrier concentration is observed, which can be stabilized by RbF‐PDT. An increase in Na and oxygen concentration in CIGS is observed for baseline and low‐Na devices, respectively, after OC stress. The oxygen concentration in CdS decreases after heat‐ and light‐soaking for devices without RbF‐PDT, whereas it remains unchanged for devices with RbF‐PDT. The atomic concentration profiles in CIGS significantly stabilize as a function of stress with the addition of RbF‐PDT.

Temporal variations of Cu(In,Ga)Se2 photovoltaic device properties during light exposure at various temperatures and voltage biases for times up to 100 h were analyzed using the kinetic theory of large lattice relaxations. Open-circuit voltage and p-type doping increased with charge injection and decreased with temperature at low injection conditions. Lattice relaxation can account for both trends and activation energies extracted from the data were approximately 0.9 and 1.2 eV for devices with lower and higher sodium content, respectively. In these devices, increased sodium content resulted in higher initial p-type doping with greater stability. First principles calculations providing revised activation energies for the (VSe − VCu) complex suggest that this defect does not account for the metastability observed here.

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