Abstract
Stacking perovskite solar cells onto crystalline silicon bottom cells in a monolithic tandem configuration enables power-conversion efficiencies (PCEs) well above those of their single-junction counterparts. However, state-of-the-art wide-band-gap perovskite films suffer from phase stability issues. Here, we show how carbazole as an additive to the perovskite precursor solution can not only reduce nonradiative recombination losses but, perhaps more importantly, also can suppress phase segregation under exposure to moisture and light illumination. This enables a stabilized PCE of 28.6% (independently certified at 28.2%) for a monolithic perovskite/silicon tandem solar cell over ∼1 cm2 and 27.1% over 3.8 cm2, built from a textured silicon heterojunction solar cell. The modified tandem devices retain ∼93% of their performance over 43 days in a hot and humid outdoor environment of almost 100% relative humidity over 250 h under continuous 1-sun illumination and about 87% during a 85/85 damp-heat test for 500 h, demonstrating the improved phase stability.
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•A strategy to suppress halide segregation and reduce nonradiative recombination loss•Certified 28.2% efficient perovskite/silicon tandem solar cells on a textured structure•Significant stability improvement upon carbazole treatment
In the past decade, the efficiency of perovskite solar cells has rapidly improved. A promising strategy to further improve efficiency is to construct tandem devices, especially when paired with Si bottom cells. The phase instability of the wide-band-gap perovskite top cell is limiting the tandem performance and also its application prospects. Thus, it is highly desirable to develop strategies to suppress the halide segregation in the perovskite layer without compromising device performance. Here, we incorporated carbazole, a nitrogen-containing heterocyclic molecule, as an additive to the perovskite layer. The carbazole treatment suppresses halide segregation, reduces nonradiative recombination loss, and lowers defect density. With an optimized 1.68 eV perovskite top cell and double-sided textured Si heterojunction bottom cell, we obtained certified 28.2% efficiency over ∼1 cm2. A series of stability tests prove that carbazole improves the long-term stability of tandem devices.
The addition of carbazole molecules in bulk perovskite layers effectively suppressed the phase segregation. Monolithic perovskite/silicon solar cells were fabricated from a textured silicon heterojunction solar cell. A stabilized PCE of 28.6% (independently certified at 28.2%) was achieved over ∼1 cm2 and 27.1% over 3.8 cm2. The long-term stability tests show the carbazole-treated tandem devices demonstrated significantly improved stability.