Typical lead‐based perovskites solar cells show an onset of photogeneration around 800 nm, leaving plenty of spectral loss in the near‐infrared (NIR). Extending light absorption beyond 800 nm into the NIR should increase photocurrent generation and further improve photovoltaic efficiency of perovskite solar cells (PSCs). Here, a simple and facile approach is reported to incorporate a NIR‐chromophore that is also a Lewis‐base into perovskite absorbers to broaden their photoresponse and increase their photovoltaic efficiency. Compared with pristine PSCs without such an organic chromophore, these solar cells generate photocurrent in the NIR beyond the band edge of the perovskite active layer alone. Given the Lewis‐basic nature of the organic semiconductor, its addition to the photoactive layer also effectively passivates perovskite defects. These films thus exhibit significantly reduced trap densities, enhanced hole and electron mobilities, and suppressed illumination‐induced ion migration. As a consequence, perovskite solar cells with organic chromophore exhibit an enhanced efficiency of 21.6%, and substantively improved operational stability under continuous one‐sun illumination. The results demonstrate the potential generalizability of directly incorporating a multifunctional organic semiconductor that both extends light absorption and passivates surface traps in perovskite active layers to yield highly efficient and stable NIR‐harvesting PSCs.
Perovskite solar cells in which 2D perovskites are incorporated within a 3D perovskite network exhibit improved stability with respect to purely 3D systems, but lower record power conversion efficiencies (PCEs). Here, a breakthrough is reported in achieving enhanced PCEs, increased stability, and suppressed photocurrent hysteresis by incorporating n‐type, low‐optical‐gap conjugated organic molecules into 2D:3D mixed perovskite composites. The resulting ternary perovskite–organic composites display extended absorption in the near‐infrared region, improved film morphology, enlarged crystallinity, balanced charge transport, efficient photoinduced charge transfer, and suppressed counter‐ion movement. As a result, the ternary perovskite–organic solar cells exhibit PCEs over 23%, which are among the best PCEs for perovskite solar cells with p–i–n device structure. Moreover, the ternary perovskite–organic solar cells possess dramatically enhanced stability and diminished photocurrent hysteresis. All these results demonstrate that the strategy of exploiting ternary perovskite–organic composite thin films provides a facile way to realize high‐performance perovskite solar cells.
more » « less- Award ID(s):
- 1903303
- NSF-PAR ID:
- 10446298
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 34
- Issue:
- 13
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The recent development of quasi‐2D perovskite solar cells have drawn significant attention due to the improved stability of these materials and devices against moisture compared to their 3D counterparts. However, the optoelectronic properties of 2D perovskites need to be optimized in order to achieve high efficiency. In this work, the effect of spacer cations, i.e., phenethylammonium (PEA), 4‐fluorophenethylammonium (F‐PEA), and 4‐methoxyphenethylammonium (MeO‐PEA) on the optoelectronic properties and device performance of quasi‐2D perovskites is systematically studied. It is observed that both larger and more hydrophobic cations can improve perovskite stability against moisture, while larger size can adversely influence the device performance. Interestingly, with F‐PEA or MeO‐PEA, distribution of
n value can be shifted toward high 3D content in quasi‐2D perovskite layers, which enables lower bandgaps and possibly lower exciton binding energy. Due to the best charge transport and lowest bandgap, the F‐PEAI‐based quasi‐2D perovskite (n = 5) solar cell shows a highest power conversion efficiency (PCE) of 14.5% with excellent stability in air with a humidity of 40–50%, keeping 90% of the original PCE after 40 d. It is believed that the approach may open a way for the design of new organic spacer cations for stable low‐dimensional hybrid perovskites with high performance. -
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n = 3 andn = 4 with NH4SCN addition. The device derived from the quasi‐2D DJ (BDA)(MA)4Pb5I16perovskite film processed with NH4SCN shows a PCE of 14.53%, which is among the highest values reported for 2D PVSCs prepared at room temperature. Moreover, the device retains 85% of its initial PCE after 900 h storage in ambient conditions with a humidity level of 50 ± 5%. These results demonstrate that this attractive approach will enable highly efficient and stable PVSCs to be made for renewable energy applications. -
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Quasi‐2D perovskites are attractive because of their improved stability compared with 3D perovskites counterparts; however, they suffer from poor performance due to the insulating organic cation spacers. To resolve this issue, a strategy of replacing the insulating spacer with conducting spacer is proposed which successfully converts the spacer from a charge‐transporting “barrier” to charge‐transporting “bridge.” Specifically, an alkyl linker‐free, fully conjugated aromatic 2,2′‐biimidazolium (BIDZ) cation is introduced as a spacer to compose quasi‐2D perovskites. Density functional theory (DFT) simulation results show that the lowest unoccupied molecular orbital (LUMO) level localizes on BIDZ and the highest occupied molecular orbital (HOMO) level is on the perovskite. However, both HOMO and LUMO levels localize on perovskite slabs for the well‐known phenethylammonium (PEA)‐based 2D perovskites. The strong electronic coupling between BIDZ and 3D perovskite slabs improves carrier mobilities even for a low‐weak‐crystallinity and random‐orientated quasi‐2D perovskite film. As a result, a remarkable power conversion efficiency up to 11.4% (
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Abstract Perovskite solar cells (PSCs) have rapidly emerged as one of the hottest topics in the photovoltaics community owing to their high power‐conversion efficiencies (PCE), and the promise to be produced at low cost. Among various PSCs, typical 3D perovskite‐based solar cells deliver high PCE but they suffer from severe instability, which restricts their practical applications. In contrast to 3D perovskites, 2D perovskites that incorporate larger, less volatile, and generally more hydrophobic organic cations exhibit much improved thermal, chemical, and environmental stability. 2D perovskites can have different roles within a solar cell, either as the primary light absorber (2D PSCs), or as a capping layer atop a 3D perovskite absorbing layer (2D/3D PSCs). Tradeoffs between PCE and stability exist in both types of PSCs—2D PSCs are more stable but exhibit lower efficiency while 2D/3D PSCs deliver exciting efficiency but show relatively poor stability. To address this PCE/stability tradeoff, the challenges both the 2D and 2D/3D PSCs face are identified and select works the community has undertaken to overcome them are highlighted in this review. It is ended with several recommendations on how to further improve PSCs so their performance and stability can be commensurate with application requirements.
