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Perovskite solar cells have emerged as a promising technology in the field of photovoltaics, owing to their notable advancements in power-conversion efficiency. Recent investigations have revealed a crucial dependency of efficiency on the source of bromide within the perovskite absorption layer. To elucidate the underlying nature of traps within these solar cells, a comprehensive series of measurements was conducted under varying light intensities. Subsequently, employing an electrodynamic theoretical model, the intrinsic processes inherent to caesium and lead-based perovskite solar cells with different bromide sources were analyzed. The study reveals significant differences in transient photocurrent measurements and photocurrent-voltage characteristics among perovskites originating from different bromide sources, measured under different light intensities. Leveraging theoretical analyses on the picosecond scale, the recombination mechanism of crystal defects was meticulously described revealing the pronounced influence of capture rates on electron-hole recombination dynamics. Furthermore, the investigation substantiated the presence of a band-bending phenomenon at the interface between the hole transport layer (HTL) and perovskite, elucidating the observed transient photocurrent phenomena. The findings significantly advance the understanding of the mechanisms underlying perovskite solar cells, offering valuable insights into their performance and paving the way for enhanced efficiency and stability in future device design and optimization.

Trap states in organic semiconductors are notoriously detrimental to the performance of organic electronics. However, the origin and energetics of trap states remain largely elusive and under debate, especially for bulk-heterojunction (BHJ) photodiodes consisting of electron donor and acceptor materials. Combining three sensitive techniques now enables locating the origin and energy of trap states in six state-of-the-art polymer – non-fullerene acceptor organic photodiodes (OPDs) with noise-based specific detectivities exceeding 1013 Jones. Analyzing the temperature dependence of the reverse-bias dark current density (Jd) identifies intra-gap states in the polymers, lying 0.3−0.4 eV above the energy of the highest occupied molecular orbital, as being responsible for Jd. Sub-bandgap external quantum efficiency spectra of donor-only and acceptor-only diodes confirm that intra-gap states are much more abundant in the polymers. Likewise, responsivity measurements at ultra-low light intensities (10−7 mW cm−2) show trap-mediated charge recombination in BHJ and polymer-only diodes, but not in acceptor-only devices. The results imply that to further improve the specific detectivity of near-infrared OPDs, the intra-gap state energy, and density need to be reduced.

Remote measurement of vital sign parameters like heartbeat and respiration rate represents a compelling challenge in monitoring an individual’s health in a noninvasive way. This could be achieved by large field-of-view, easy-to-integrate unobtrusive sensors, such as large-area thin-film photodiodes. At long distances, however, discriminating weak light signals from background disturbance demands superior near-infrared (NIR) sensitivity and optical noise tolerance. Here, we report an inherently narrowband solution–processed, thin-film photodiode with ultrahigh and controllable NIR responsivity based on a tandem-like perovskite-organic architecture. The device has low dark currents (<10 −6 mA cm −2), linear dynamic range >150 dB, and operational stability over time (>8 hours). With a narrowband quantum efficiency that can exceed 200% at 850 nm and intrinsic filtering of other wavelengths to limit optical noise, the device exhibits higher tolerance to background light than optically filtered silicon-based sensors. We demonstrate its potential in remote monitoring by measuring the heart rate and respiration rate from distances up to 130 cm in reflection.

Low-dimensional perovskites attract increasing interest due to tunable optoelectronic properties and high stability. Here, it is shown that perovskite thin films with a vertical gradient in dimensionality result in graded electronic bandgap structures that are ideal for photodiode applications. Positioning low-dimensional, vertically-oriented perovskite phases at the interface with the electron blocking layer increases the activation energy for thermal charge generation and thereby effectively lowers the dark current density to a record-low value of 5 × 10−9 mA cm−2 without compromising responsivity, resulting in a noise-current-based specific detectivity exceeding 7 × 1012 Jones at 600 nm. These multidimensional perovskite photodiodes show promising air stability and a dynamic range over ten orders of magnitude, and thus represent a new generation of high-performance low-cost photodiodes.

Solution-processed quasi-2D perovskites are promising for stable and efficient solar cells because of their superior environmental stability compared to 3D perovskites and tunable optoelectronic properties. Changing the number of inorganic layers (n) sandwiched between the organic spacers allows for tuning of the bandgap. However, narrowing the phase distribution around a specific n-value is a challenge. In-situ UV–vis–NIR absorption spectroscopy is used to time-resolve the crystallization dynamics of quasi-2D butylammonium-based (BA) perovskites with = 4, processed from N,N-dimethylformamide (DMF) in the presence of different co-solvents. By combining with photoluminescence, transient absorption, and grazing-incidence wide-angle X-ray scattering, the crystallization is correlated to the distribution of phases with different n-values. Infrared spectroscopy and density functional theory reveal that the phase distribution correlates with perovskite precursor—co-solvent interaction energies and that stronger interactions shift the phase distribution towards smaller n-values. Careful tuning of the solvent/co-solvent ratio provides a more homogeneous phase distribution, with highly oriented perovskite crystals and suppressed formation of n = 1–2 phases, providing a power conversion efficiency for BA2MA3Pb4I13 solar cells that increases from 3.5% when processed from DMF to over 11% and 10% when processed from DMF/dimethyl sulfoxide and DMF/N-methyl-2-pyrrolidone mixtures, respectively., ChemE/Opto-electronic Materials

Solution-processed quasi-2D perovskites are promising for stable and efficient solar cells because of their superior environmental stability compared to 3D perovskites and tunable optoelectronic properties. Changing the number of inorganic layers (n) sandwiched between the organic spacers allows for tuning of the bandgap. However, narrowing the phase distribution around a specific n-value is a challenge. In-situ UV–vis–NIR absorption spectroscopy is used to time-resolve the crystallization dynamics of quasi-2D butylammonium-based (BA) perovskites with = 4, processed from N,N-dimethylformamide (DMF) in the presence of different co-solvents. By combining with photoluminescence, transient absorption, and grazing-incidence wide-angle X-ray scattering, the crystallization is correlated to the distribution of phases with different n-values. Infrared spectroscopy and density functional theory reveal that the phase distribution correlates with perovskite precursor—co-solvent interaction energies and that stronger interactions shift the phase distribution towards smaller n-values. Careful tuning of the solvent/co-solvent ratio provides a more homogeneous phase distribution, with highly oriented perovskite crystals and suppressed formation of n = 1–2 phases, providing a power conversion efficiency for BA2MA3Pb4I13 solar cells that increases from 3.5% when processed from DMF to over 11% and 10% when processed from DMF/dimethyl sulfoxide and DMF/N-methyl-2-pyrrolidone mixtures, respectively.