Fig. 1. (Color online) The PCE evolution of single-junction PSCs and all-perovskite tandem solar cells.

Fig. 2. (Color online) (a) Schematic structure of monolithic all-perovskite tandem solar cells. (b) Absorption of different wavelengths of light by different bandgap subcells. (c) Solar irradiance spectrum showing the spectral regions over which the two semiconductors could absorb. Reproduced with permission^[56]. (d) Theoretical efficiency limit for monolithic all-perovskite tandem solar cells, calculated with different subcell thicknesses, each picked to optimize the performance for each bandgap combination. Reproduced with permission^[23].

Fig. 3. (Color online) Schematic of the structure and bandgap tuning of perovskite. (a) Perovskite structure and selectable bandgap tuning ions. (b) UV–vis absorption spectra of the MAPb(I_1–xBr_x)₃. Reproduced with permission^[60]. (c) UV–vis absorbance spectra of the FAPbI_yBr_3–y. Reproduced with permission^[24]. (d) Absorption onset in CsPb(Br_xI_1–x)₃ with increasing bromine content. Reproduced with permission^[21]. (e) UV–vis absorbance spectra of perovskite films made with increasing DMA percentage of the A-site, with 0% bromine (top) and 20% bromine (below). DMA addition was compensated in an equimolar manner with addition of Cs. Reproduced with permission^[63]. (f) Bandgap values obtained from the Tauc plot and PL spectra of FASn_xPb_1−xI₃ perovskites (top); bandgap values calculated using the first-principles method (bottom). Reproduced with permission^[53]. (g) PL spectra of (FASnI₃)_x(MAPbI₃)_1–x with different x values. Reproduced with permission^[68].

Fig. 4. (Color online) Schematic structures of all-perovskite tandem solar cells with different tunnel recombination junctions. (a) Structure of a tandem solar cell with a lamination for connecting subcells. Reproduced with permission^[52]. (b) Structure of a tandem solar cell using PEDOT:PSS as the charge recombination layer. Reproduced with permission^[79]. (c) Structure of a tandem solar cell using TaTm:F6-TCNNQ as the charge recombination layer. Reproduced with permission^[72]. (d) Structure of a tandem solar cell using spiro-OMeTAD/PEDOT: PSS/PEI/PCBM: PEI as the tunnel recombination junction. Reproduced with permission^[74]. (e) Cross-section SEM images of a tandem solar cell using ITO as the charge recombination layer and SnO₂ as the buffer layer. Reproduced with permission^[53]. (f) Structure of a tandem solar cell using ITO as the charge recombination layer and Bis-C₆₀ as the buffer layer. Reproduced with permission^[73]. (g) Structure of a tandem solar cell using ITO as the charge recombination layer and Ag/MoO₃ as the buffer layer. Reproduced with permission^[76]. (h) Cross-sectional SEM of a tandem solar cell using AZO/IZO as the charge recombination layer. Reproduced with permission^[63]. (i) Structure of a tandem solar cell using Au/SnO₂ as the tunnel recombination junction. Reproduced with permission^[54].

Fig. 5. (Color online) Performance of all-perovskite tandem solar cell with improved performance in the wide-bandgap top subcell. (a) J–V cures of tandem solar cell using FA_0.83Cs_0.17Pb (I_0.5Br_0.5)₃ as the top subcell. Reproduced with permission^[53]. (b) J–V cures of tandem solar cell using MA_0.9Cs_0.1Pb(I_0.6Br_0.4) as the top subcell. Reproduced with permission^[73]. (c) J–V cures of tandem solar cell using DMA_0.1FA_0.6Cs_0.3PbI_2.4Br_0.6 as the top subcell. Reproduced with permission^[63].

Fig. 6. (Color online) Performance of all-perovskite tandem solar cell with improved performance in the narrow-bandgap bottom subcell. (a, b) EQE and J–V cures of a tandem solar cell using FA_0.75Cs_0.25Sn_0.5Pb_0.5I₃ as the bottom subcell. Reproduced with permission^[75]. (c, d) EQE and J–V cures of a tandem solar cell using (FASnI₃)_0.6 (MAPbI₃)_0.4-2.5%Cl as the bottom subcell. Reproduced with permission^[76]. (e, f) EQE and J–V cures of a tandem solar cell using Cd-FA_0.5MA_0.45Cs_0.05Pb_0.5Sn_0.5I₃ as the bottom subcell. Reproduced with permission^[90]. (g) EQE and J–V cures of a tandem solar cell using (FASnI₃)_0.6(MAPbI₃)_0.4 as the bottom subcell. Reproduced with permission^[77]. (h–j) EQE and J–V cures and MPP of a tandem solar cell using FA_0.7MA_0.3Pb_0.5Sn_0.5I₃ as the bottom subcell. Reproduced with permission^[54].

Table 1. Structure, bandgap matching, and performance parameters of all-perovskite tandem solar cells.