Organic-inorganic hybrid perovskite multijunction solar cells have immense potential to realize power conversion efficiencies (PCEs) beyond the Shockley-Queisser limit of single-junction solar cells; however, they are limited by large nonideal photovoltage loss (V ) in small- and large-bandgap subcells. Here, an integrated approach is utilized to improve the V of subcells with optimized bandgaps and fabricate perovskite-perovskite tandem solar cells with small V . A fullerene variant, Indene-C bis-adduct, is used to achieve optimized interfacial contact in a small-bandgap (≈1.2 eV) subcell, which facilitates higher quasi-Fermi level splitting, reduces nonradiative recombination, alleviates hysteresis instabilities, and improves V to 0.84 V. Compositional engineering of large-bandgap (≈1.8 eV) perovskite is employed to realize a subcell with a transparent top electrode and photostabilized V of 1.22 V. The resultant monolithic perovskite-perovskite tandem solar cell shows a high V of 1.98 V (approaching 80% of the theoretical limit) and a stabilized PCE of 18.5%. The significantly minimized nonideal V is better than state-of-the-art silicon-perovskite tandem solar cells, which highlights the prospects of using perovskite-perovskite tandems for solar-energy generation. It also unlocks opportunities for solar water splitting using hybrid perovskites with solar-to-hydrogen efficiencies beyond 15%.
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
halide hybrid perovskites are of significant interest because
their bandgap can be tuned as a current-matched top-cell in tandem
photovoltaics. However, several mixed halide perovskites phase segregate
under illumination, exhibit large voltage deficits, and produce unstable
photocurrents. We investigate the origin of phase segregation and
implication for tandems with mixed halide large-bandgap (∼1.75
eV) perovskites. We show explicitly that MAPb(I0.6Br0.4)3 and (MA0.9,Cs0.1)Pb(I0.6,Br0.4)3, termed “MA”
and “MACs”, respectively, rapidly phase segregate in
the dark upon 1 sun equivalent current injection. This is direct experimental
evidence that conduction band electrons or valence band holes are
the culprit behind phase segregation. In contrast, (FA0.83,Cs0.17)Pb(I0.66,Br0.34)3, or “FACs,” prepared at only 75 °C resists phase
segregation below 4 sun injection. FACs prepared at 165 °C yields
larger grains and withstands higher injected carrier concentrations
before phase segregation. The FACs and MACs devices sustain near constant
power output at 1 sun and do not affect the current output of a CIGS
bottom cell when used as an incident light filter.
The
polycrystalline feature of solution-processed perovskite film
and its ionic nature inevitably incur substantial crystallographic
defects, especially at the film surface and the grain boundaries (GBs).
Here, a simple defect passivation method was exploited by post-treating
CH3NH3PbI3 (MAPbI3) film
with a rationally selected diammonium iodide. The molecular structure
of the used diammonium iodide was discovered to play a critical role
in affecting the phase purity of treated MAPbI3. Both NH3I(CH2)4NH3I and NH3I(CH2)2O(CH2)2NH3I (EDBE) induce three-dimensional (3D) to two-dimensional (2D) perovskite
phase transformation during the treatment while only NH3I(CH2)8NH3I (C8) successfully passivates
perovskite surface and GBs without forming 2D perovskite because of
the elevated activation energy arising from its unique anti–gauche
isomerization. Defect passivation of MAPbI3 was clearly
confirmed by scanning Kelvin probe microscopy (SKPM) and time-resolved photoluminescence (TRPL)
studies, which results in the reduced recombination loss in derived
devices. Consequently, the perovskite solar cell with C8 passivation
showed a much improved power conversion efficiency (PCE) of 17.60%
compared to the control device PCE of 14.64%.
High-efficiency and low-cost perovskite solar cells (PVKSCs) are an ideal candidate for addressing the scalability challenge of solar-based renewable energy. The dynamically evolving research field of PVKSCs has made immense progress in solving inherent challenges and capitalizing on their unique structure-property-processing-performance traits. This review offers a unique outlook on the paths toward commercialization of PVKSCs from the interfacial engineering perspective, relevant to both specialists and nonspecialists in the field through a brief introduction of the background of the field, current state-of-the-art evolution, and future research prospects. The multifaceted role of interfaces in facilitating PVKSC development is explained. Beneficial impacts of diverse charge-transporting materials and interfacial modifications are summarized. In addition, the role of interfaces in improving efficiency and stability for all emerging areas of PVKSC design are also evaluated. The authors' integral contributions in this area are highlighted on all fronts. Finally, future research opportunities for interfacial material development and applications along with scalability-durability-sustainability considerations pivotal for facilitating laboratory to industry translation are presented.
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