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October 31, 2024

Cation reactivity inhibits perovskite degradation in efficient and stable solar modules

Science, 31 Oct 2024, Vol 386, Issue 6721, pp. 531-538. We show that incorporating N,N-dimethylmethyleneiminium chloride into the perovskite precursor solution formed dimethylammonium cation and that previously unobserved methyl tetrahydrotriazinium ([MTTZ]+) cation effectively improved perovskite film. The in situ formation of [MTTZ]+ cation increased the formation energy of iodine vacancies and enhanced the migration energy barrier of iodide and cesium ions, which suppressed nonradiative recombination, thermal decomposition, and phase segregation processes. The optimized PSMs achieved a record (certified) PCE of 23.2% with an aperture area of 27.2 cm2, with a stabilized PCE of 23.0%. The encapsulated PSM retained 87.0% of its initial PCE after ~1900 hours of maximum power point tracking at 85°C and 85% relative humidity under 1.0-sun illumination.

July 24, 2024

peri-Fused polyaromatic molecular contacts for perovskite solar cells

Nature volume 632, pages301–306 (2024) Molecule-based selective contacts have become a crucial component to ensure high-efficiency inverted perovskite solar cells1,2,3,4,5. These molecules always consist of a conjugated core with heteroatom substitution to render the desirable carrier-transport capability6,7,8,9. So far, the design of successful conjugation cores has been limited to two N-substituted π-conjugated structures, carbazole and triphenylamine, with molecular optimization evolving around their derivatives2,5,10,11,12. However, further improvement of the device longevity has been hampered by the concomitant limitations of the molecular stability induced by such heteroatom-substituted structures13,14.

June 21, 2023

Oriented nucleation in formamidinium perovskite for photovoltaics

Nature volume 620, pages323–327 (2023) The black phase of formamidinium lead iodide (FAPbI3) perovskite shows huge promise as an efficient photovoltaic, but it is not favoured energetically at room temperature, meaning that the undesirable yellow phases are always present alongside it during crystallization1,2,3,4. This problem has made it difficult to formulate the fast crystallization process of perovskite and develop guidelines governing the formation of black-phase FAPbI3 (refs. 5,6). Here we use in situ monitoring of the perovskite crystallization process to report an oriented nucleation mechanism that can help to avoid the presence of undesirable phases and improve the performance of photovoltaic devices in different film-processing scenarios. The resulting device has a demonstrated power-conversion efficiency of 25.4% (certified 25.0%) and the module, which has an area of 27.83 cm2, has achieved an impressive certified aperture efficiency of 21.4%.

March 15, 2022

Stability-limiting heterointerfaces of perovskite photovoltaics

Nature volume 605, pages268–273 (2022) Optoelectronic devices consist of heterointerfaces formed between dissimilar semiconducting materials. The relative energy-level alignment between contacting semiconductors determinately affects the heterointerface charge injection and extraction dynamics. For perovskite solar cells (PSCs), the heterointerface between the top perovskite surface and a charge-transporting material is often treated for defect passivation1,2,3,4 to improve the PSC stability and performance. However, such surface treatments can also affect the heterointerface energetics1. Here we show that surface treatments may induce a negative work function shift (that is, more n-type), which activates halide migration to aggravate PSC instability. Therefore, despite the beneficial effects of surface passivation, this detrimental side effect limits the maximum stability improvement attainable for PSCs treated in this way.

February 5, 2021

Reconfiguring the band-edge states of photovoltaic perovskites by conjugated organic cations

Science 5 Feb 2021, Vol 371, Issue 6529, pp. 636-640. The band edge of hybrid organic-inorganic perovskites, which have the general formula ABX3, is mainly controlled by the inorganic X anions (such as chloride) and the B cation (such as lead). Organic A-site cations usually only exert indirect structural effects because their electronic levels lie far from the band edge. Xue et al. show that cations with large π-conjugated structures can interact with inorganic frontier molecular orbitals. A surface layer of ethylammonium pyrene, which had an optimal intercalation distance, increased hole mobilities and power conversion efficiencies relative to a reference inorganic perovskite and also improved device stability.

December 20, 2019

Constructive molecular configurations for surface-defect passivation of perovskite photovoltaics

Science 20 Dec 2019, Vol 366, Issue 6472, pp.1509-1513. Unproductive charge recombination at surface defects can limit the efficiency of hybrid perovskite solar cells, but these defects can be passivated by the binding of small molecules. Wang et al. studied three such small molecules—theophylline, caffeine, and theobromine—that bear both carbonyl and amino groups. For theophylline, hydrogen bonding of the amino hydrogen to surface iodide optimized the carbonyl interaction with a lead antisite defect and improved the efficiency of a perovskite cell from 21 to 22.6%.