Stable Low‐Bandgap Pb–Sn Binary Perovskites for Tandem Solar Cells

Abstract

A low-bandgap (1.33 eV) Sn-based MA FA Pb Sn I perovskite is developed via combined compositional, process, and interfacial engineering. It can deliver a high power conversion efficiency (PCE) of 14.19%. Finally, a four-terminal all-perovskite tandem solar cell is demonstrated by combining this low-bandgap cell with a semitransparent MAPbI cell to achieve a high efficiency of 19.08%.

Mixed‐Organic‐Cation Tin Iodide for Lead‐Free Perovskite Solar Cells with an Efficiency of 8.12%

“…Therefore, we speculate that oxidation may cause the lowering of their VBM and that the −5.9 to −6.0 eV results may be obtained after the FASnI 3 film is heavily oxidized. It is also worth noting that the VBM values of many papers regarding FASnI 3 or MASnI 3 have reported their VBM to be around −4.8 eV,12, 15, 21, 30 which are in good agreement with our results. We herein emphasize the importance to minimize oxidation during the VBM measurements of Sn‐based perovskites.…”

“…We measured the absorption spectra of the (FA) x (MA) 1 −x SnI 3 films on quartz substrates (Figure 1c). The absorption onsets of the Sn‐based perovskites are quite indistinct, which may be ascribed to the formation of sub‐bandgap states as a result of the oxidation of Sn 2+ during the measurement in air,12, 27 making it difficult to determine their optical bandgaps. Therefore, we obtained the steady‐state photoluminescent (PL) spectra of the encapsulated perovskite films (Figure 1d) to access their bandgaps, which calculated from the PL emission peaks are 1.26, 1.28, 1.30, 1.33, and 1.36 eV for x = 0.00, 0.25, 0.50, 0.75, and 1.00, respectively, showing a growing trend as the FA contents increases.…”

“…Tin (Sn)‐based perovskites, being structurally similar to their Pb‐based counterparts, have attracted wide attention recently. With slightly narrower bandgaps (≈1.3 eV) compared to their Pb‐based counterparts,11, 12 Sn‐based perovskites promise higher short‐circuit current densities ( J sc ) as well as a theoretical PCE limit that is very close to 33%. However, the efficiency of Sn‐based PSCs, though outperforming other Pb‐free candidates, still lags behind Pb‐based ones, which can be attributed to several reasons.…”

Optical response of mixed methylammonium lead iodide and formamidinium tin iodide perovskite thin films

“…CPs obtained for MAPbI 3 from this analysis are similar to those obtained by analysis of the second derivative reported in literature. 15 Additional CPs at 1.72, 2.45, 3.09, and 5.67 eV also appear here for MAPbI 3 . The sensitivity to additional CPs and differences in position may be attributed due to different fitting procedures and relative purity of the samples.…”

Fabrication and characterization of CH3NH3(Cs)Pb(Sn)I3(Cl) perovskite solar cells with TiO2 nanoparticle layers

“…21) When the Pb was substituted by Sn, the range of optical absorption increased, and the bandgap energy decreased for CH 3 -NH 3 Pb 1−x Sn x I 3 . [22][23][24][25][26][27] Although an improvement of the shortcircuit current density was expected by Sn substitution, the conversion efficiencies were reported to be less than those of Pb-based perovskite solar cells. 22) The addition of another halogen such as Br or Cl could improve the photovoltaic performance of MAPbI 3 .…”