Advancing all-perovskite two-terminal tandem solar cells: optimization of wide- and narrow-bandgap perovskites and interconnecting layers

Perovskite solar cells (PSCs) have attracted tremendous attention due to their impressive power conversion efficiency (PCE). After extensive device engineering efforts, the PCE of single junction PSCs has reached 26.7% from the initial value of 3.8%. Owing to the unique characteristics of metal halide perovskites (MHPs), such as a tunable energy bandgap, bandgap complementary engineering can be applied to MHPs by pairing wide-bandgap (WBG) perovskite with narrow-bandgap (NBG) perovskite in series to form all-perovskite two-terminal tandem solar cells (all-Pe-2T-TSCs), which are expected to overcome the Shockley–Queisser limit. In a tandem architecture, the WBG perovskite and NBG perovskite act as the top and bottom absorbers, respectively, with the interconnecting layer (ICL) facilitating electron–hole recombination. Currently, (i) the huge V_OC deficit and severe photo-induced phase separation in WBG perovskite, (ii) the fast oxidation and uncontrollable crystallization of tin in NBG perovskite and (iii) the optical parasitic absorption losses in the ICL are the key challenges hindering the performance development of all-Pe-2T-TSCs. In this review, a thorough discussion is given to address the issues mentioned above through an analysis of previously published research. Finally, new viewpoints on boosting the PCE and stability of all-Pe-2T-TSCs are discussed, intending to guide readers in developing efficient and stable all-Pe-2T-TSCs.