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Long-term durability is critically important for the commercialization of perovskite solar cells (PSCs). The ionic character of the perovskite and the hydrophilicity of commonly used additives for the hole-transporting layer (HTL), such as lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and tert -butylpyridine ( t BP), render PSCs prone to moisture attack, compromising their long-term stability. Here we introduce a trifluoromethylation strategy to overcome this drawback and to boost the PSC's solar to electric power conversion efficiency (PCE). We employ 4-(trifluoromethyl)benzylammonium iodide (TFMBAI) as an amphiphilic modifier for interfacial defect mitigation and 4-(trifluoromethyl)pyridine (TFP) as an additive to enhance the HTL's hydrophobicity. Surface treatment of the triple-cation perovskite with TFMBAI largely suppressed the nonradiative charge carrier recombination, boosting the PCE from 20.9% to 23.9% and suppressing hysteresis, while adding TFP to the HTL enhanced the PCS's resistance to moisture while maintaining its high PCE. Taking advantage of the synergistic effects resulting from the combination of both fluoromethylated modifiers, we realize TFMBAI/TFP-based highly efficient PSCs with excellent operational stability and resistance to moisture, retaining over 96% of their initial efficiency after 500 h maximum power point tracking (MPPT) under simulated 1 sun irradiation and 97% of their initial efficiency after 1100 h of exposure under ambient conditions to a relative humidity of 60-70%.

The use of molecular modulators to reduce the defect density at the surface and grain boundaries of perovskite materials has been demonstrated to be an effective approach to enhance the photovoltaic performance and device stability of perovskite solar cells. Herein, we employ crown ethers to modulate perovskite films, affording passivation of undercoordinated surface defects. This interaction has been elucidated by solid-state nuclear magnetic resonance and density functional theory calculations. The crown ether hosts induce the formation of host-guest complexes on the surface of the perovskite films, which reduces the concentration of surface electronic defects and suppresses nonradiative recombination by 40%, while minimizing moisture permeation. As a result, we achieved substantially improved photovoltaic performance with power conversion efficiencies exceeding 23%, accompanied by enhanced stability under ambient and operational conditions. This work opens a new avenue to improve the performance and stability of perovskite-based optoelectronic devices through supramolecular chemistry.

Shortwave infrared colloidal quantum dots (SWIR-CQDs) are semiconductors capable of harvesting across the AM1.5G solar spectrum. Today's SWIR-CQD solar cells rely on spin-coating; however, these films exhibit cracking once thickness exceeds ∼500 nm. We posited that a blade-coating strategy could enable thick QD films. We developed a ligand exchange with an additional resolvation step that enabled the dispersion of SWIR-CQDs. We then engineered a quaternary ink that combined high-viscosity solvents with short QD stabilizing ligands. This ink, blade-coated over a mild heating bed, formed micron-thick SWIR-CQD films. These SWIR-CQD solar cells achieved short-circuit current densities (Jsc) that reach 39 mA cm -2 , corresponding to the harvest of 60% of total photons incident under AM1.5G illumination. External quantum efficiency measurements reveal both the first exciton peak and the closest Fabry-Perot resonance peak reaching approximately 80%-this is the highest unbiased EQE reported beyond 1400 nm in a solution-processed semiconductor.

Colloidal quantum dots (CQDs) allow broad tuning of the bandgap across the visible and near-infrared spectral regions. Recent advances in applying CQDs in light sensing, photovoltaics, and light emission have heightened interest in achieving further synthetic improvements. In particular, improving monodispersity remains a key priority in order to improve solar cells' open-circuit voltage, decrease lasing thresholds, and improve photodetectors' noise-equivalent power. Here we utilize machine-learning-in-the-loop to learn from available experimental data, propose experimental parameters to try, and, ultimately, point to regions of synthetic parameter space that will enable record-monodispersity PbS quantum dots. The resultant studies reveal that adding a growth-slowing precursor (oleylamine) allows nucleation to prevail over growth, a strategy that enables record-large-bandgap (611 nm exciton) PbS nanoparticles with a well-defined excitonic absorption peak (half-width at half-maximum (hwhm) of 145 meV). At longer wavelengths, we also achieve improved monodispersity, with an hwhm of 55 meV at 950 nm and 24 meV at 1500 nm, compared to the best published to date values of 75 and 26 meV, respectively.

Colloidal quantum dots are promising materials for tandem solar cells that complement silicon and perovskites. These devices are fabricated from solution phase; however, existing methods for making infrared-bandgap CQD inks suffer agglomeration and fusion during solution exchange. Here we develop a ligand exchange that provides robust surface protection and thereby avoids aggregation. First, we exchanged long oleic acid ligands to a mixed system comprising medium-chain ammonium and anionic chloride ligands; we then reshelled the surface using short halides and pseudohalide ligands that enabled transfer to a polar solvent. Absorbance and photoluminescence measurements reveal the retention of exciton sharpness, whereas X-ray photoelectron spectroscopy indicates halide capping. The best power conversion efficiency of these devices is 0.76 power points after filtering through silicon, which is 1.9× higher than previous single-step solution-processed IR-CQD solar cells.

Unintentional self-doping in semiconductors through shallow defects is detrimental to optoelectronic device performance. It adversely affects junction properties and it introduces electronic noise. This is especially acute for solution-processed semiconductors, including hybrid perovskites, which are usually high in defects due to rapid crystallization. Here, we uncover extremely low self-doping concentrations in single crystals of the two-dimensional perovskites (C 6 H 5 C 2 H 4 NH 3 ) 2 PbI 4 ·(CH 3 NH 3 PbI 3 ) n-1 (n = 1, 2, and 3), over three orders of magnitude lower than those of typical three-dimensional hybrid perovskites, by analyzing their conductivity behavior. We propose that crystallization of hybrid perovskites containing large organic cations suppresses defect formation and thus favors a low self-doping level. To exemplify the benefits of this effect, we demonstrate extraordinarily high light-detectivity (10 13 Jones) in (C 6 H 5 C 2 H 4 NH 3 ) 2 PbI 4 ·(CH 3 NH 3 PbI 3 ) n-1 photoconductors due to the reduced electronic noise, which makes them particularly attractive for the detection of weak light signals. Furthermore, the low self-doping concentration reduces the equilibrium charge carrier concentration in (C 6 H 5 C 2 H 4 NH 3 ) 2 PbI 4 ·(CH 3 NH 3 PbI 3 ) n-1 , advantageous in the design of p-i-n heterojunction solar cells by optimizing band alignment and promoting carrier depletion in the intrinsic perovskite layer, thereby enhancing charge extraction.

Colloidal quantum dot (CQD) materials are of interest in thin-film solar cells due to their size-tunable bandgap and low-cost solution-processing. However, CQD solar cells suffer from inefficient charge extraction over the film thicknesses required for complete absorption of solar light. Here we show a new strategy to enhance light absorption in CQD solar cells by nanostructuring the CQD film itself at the back interface. We use two-dimensional finite-difference time-domain (FDTD) simulations to study quantitatively the light absorption enhancement in nanostructured back interfaces in CQD solar cells. We implement this experimentally by demonstrating a nanoimprint-transfer-patterning (NTP) process for the fabrication of nanostructured CQD solids with highly ordered patterns. We show that this approach enables a boost in the power conversion efficiency in CQD solar cells primarily due to an increase in short-circuit current density as a result of enhanced absorption through light-trapping.