Triple-halide wide–band gap perovskites with suppressed phase segregation for efficient tandems

Abstract

Wide–band gap metal halide perovskites are promising semiconductors to pair with silicon in tandem solar cells to pursue the goal of achieving power conversion efficiency (PCE) greater than 30% at low cost. However, wide–band gap perovskite solar cells have been fundamentally limited by photoinduced phase segregation and low open-circuit voltage. We report efficient 1.67–electron volt wide–band gap perovskite top cells using triple-halide alloys (chlorine, bromine, iodine) to tailor the band gap and stabilize the semiconductor under illumination. We show a factor of 2 increase in photocarrier lifetime and charge-carrier mobility that resulted from enhancing the solubility of chlorine by replacing some of the iodine with bromine to shrink the lattice parameter. We observed a suppression of light-induced phase segregation in films even at 100-sun illumination intensity and less than 4% degradation in semitransparent top cells after 1000 hours of maximum power point (MPP) operation at 60°C. By integrating these top cells with silicon bottom cells, we achieved a PCE of 27% in two-terminal monolithic tandems with an area of 1 square centimeter.

Iodine (I) Expulsion at Photoirradiated Mixed Halide Perovskite Interface. Should I Stay or Should I Go?

“…1−4 Hence, they are potentially important in the construction of tandem solar cells. 5 An interesting behavior of metal halide perovskites is the mobility of halide ions in solid films. The movement of halide ions which become mobile under light irradiation, 6−8 electrical bias, 8−10 or the influence of heat 11−13 can be probed through electrical 14,15 and microwave conductivity, 16 electrochemical impedance, 17−19 and optical spectroscopic 7,20−25 measurements.…”

“…As discussed in previous studies, 23,26 these absorption changes indicate photoinduced segregation of halide ions to form bromide-rich and iodide-rich domains (reactions 1 and 2) → + 2MAPbBr I MAPbBr MAPbI hv 1.5 1. 5 3 3…”

Stable Perovskite Solar Cells Enabled by Simultaneous Surface and Bulk Defects Passivation

“…This may arise from the excessive CsBr‐induced phase separation, which leads to the formation of Br‐rich and I‐rich perovskite phases. [ 27 ] Based on these results, we speculate that during the CsBr/methanol solution treatment, methanol acts as the corrosive reagent to first open the perovskite structure, then Cs + and Br − restore the stoichiometry and passivate the corresponding defects. When the concentration of CsBr/methanol is proper, i.e., CsBr‐5 film, the treatment can achieve dynamic equilibrium to deliver the best modification effect.…”

“…When the concentration of CsBr/methanol solution increased continuously from the desired 5 mg mL −1 to high concentrations, the inverse redshift of absorption edge can be attributed to the phase segregation caused by the excessive Br − . [ 27 ] The increase in the bandgap is theoretically favorable to improve the V OC of devices. The normalized steady‐state photoluminescence (PL) in Figure S7, Supporting Information shows the same peak‐shift trend with the absorption edge, cross‐checking that CsBr treatment could change the composition of perovskite film to affect its semiconducting properties.…”

“…The performance drop in the high CsBr‐concentration region can be assigned to the excess CsBr‐induced phase segregation, as indicated by the XRD results in Figure 3b. [ 27 ] Figure 3h,i and Figure S8, Supporting Information show the statistics of photovoltaic parameters (PCE, V OC , J SC , and FF) based on various devices. J SC shows a minor variation in the range of 20.95 to 21.50 mA cm −2 (Figure S8a, Supporting Information), whereas the evolution of V OC (Figure 3i) and FF (Figure S7b, Supporting Information) present the same trend as the PCEs.…”