Advances in Perovskite Optoelectronics: Bridging the Gap Between Laboratory and Fabrication

In 2019, hybrid halide perovskites celebrated their 10th anniversary as a "wonder material" for optoelectronic applications. Although the parent perovskite structures were elucidated in the late 19th century, the seminal work by Miyasaka et al. exploiting organic‐inorganic hybrid halide perovskites sensitizers for visible‐light conversion in solar cells marked the revisit of these materials and has proven to be a game‐changer in this field. Extensive investigations were undertaken to develop new materials (all inorganic and organic‐inorganic hybrids, in the form of films or alternate morphologies) and deposition techniques, explore interfaces and in‐depth characterization, while engineering devices and testing methods for optimum results. Within a short time span, the power conversion efficiency (PCE) of single‐junction and tandem perovskite solar cells (PSCs) have exceeded 25% and 29% respectively; thus challenging the dominance of silicon solar cells. Building‐integrated photovoltaics (BIPV) is another hot topic in PSCs, where perovskite solar cells are designed to be semi‐transparent for deployment in residential or office building facades. Along with the success in photovoltaics, halide perovskites have also made their impact in light emission, lasing, imaging, spintronics, memristors, and photocatalysis. However, key challenges still lie ahead, particularly on the commercialization of perovskite devices. Poor material and device stability under operational conditions and the lack of reproducibility and scalability have remained problematic; whereas the search for suitable lead‐free perovskites continues

Polaron Self-localization in White-light Emitting Hybrid Perovskites

Two-dimensional (2D) perovskites with general formula $APbX_4$ are attracting increasing interest as solution processable, white-light emissive materials. Recent studies have shown that their broadband emission is related to the formation of intra-gap color centers; however, the nature and dynamics of the emissive species have remained elusive. Here we show that the broadband photoluminescence of the 2D perovskites $(EDBE)PbCl_4$ and $(EDBE)PbBr_4$ stems from the localization of small polarons within the lattice distortion field. Using a combination of spectroscopic techniques and first-principles calculations, we infer the formation of ${Pb_2}^{3+}$, $Pb^{3+}$, and ${X_2}^-$ (where X=Cl or Br) species confined within the inorganic perovskite framework. Due to strong Coulombic interactions, these species retain their original excitonic character and form self-trapped polaron-excitons acting as radiative color centers. These findings are expected to be applicable to a broad class of white-light emitting perovskites with large polaron relaxation energy.Comment: 34 pages, 15 figures, 3 table

Computational Study of Halide Perovskite-Derived A2_2BX6_6 Inorganic Compounds: Chemical Trends in Electronic Structure and Structural Stability

The electronic structure and energetic stability of A$_2$BX$_6$ halide compounds with the cubic and tetragonal variants of the perovskite-derived K$_2$PtCl$_6$ prototype structure are investigated computationally within the frameworks of density-functional-theory (DFT) and hybrid (HSE06) functionals. The HSE06 calculations are undertaken for seven known A$_2$BX$_6$ compounds with A = K, Rb and Cs, and B = Sn, Pd, Pt, Te, and X = I. Trends in band gaps and energetic stability are identified, which are explored further employing DFT calculations over a larger range of chemistries, characterized by A = K, Rb, Cs, B = Si, Ge, Sn, Pb, Ni, Pd, Pt, Se and Te and X = Cl, Br, I. For the systems investigated in this work, the band gap increases from iodide to bromide to chloride. Further, variations in the A site cation influences the band gap as well as the preferred degree of tetragonal distortion. Smaller A site cations such as K and Rb favor tetragonal structural distortions, resulting in a slightly larger band gap. For variations in the B site in the (Ni, Pd, Pt) group and the (Se, Te) group, the band gap increases with increasing cation size. However, no observed chemical trend with respect to cation size for band gap was found for the (Si, Sn, Ge, Pb) group. The findings in this work provide guidelines for the design of halide A$_2$BX$_6$ compounds for potential photovoltaic applications

Answers and Solutions

Answers and solutions to the puzzles in this issue

Surface Recombination and Collection Efficiency in Perovskite Solar Cells from Impedance Analysis

The large diffusion lengths recurrently measured in perovskite single crystals and films signal small bulk nonradiative recombination flux and locate the dominant carrier recombination processes at the outer interfaces. Surface recombination largely determines the photovoltaic performance, governing reductions under short-circuit current and open-circuit voltage. Quantification of recombination losses is necessary to reach full understanding of the solar cell operating principles. Complete impedance model is given, which connects capacitive and resistive processes to the electronic kinetics at the interfaces. Carrier collection losses affecting the photocurrent have been determined to equal 1%. Photovoltage loss is linked to the decrease in surface hole density, producing 0.3 V reduction with respect to the ideal radiative limit. Our approach enables a comparison among different structures, morphologies, and processing strategies of passivation and buffer layers.We acknowledge financial support by Ministerio de Economía y Competitividad (MINECO) of Spain under project (MAT2016-76892-C3-1-R) and Generalitat Valenciana (Prometeo/2014/020). SCIC at UJI is also acknowledged

Hot carrier extraction in CH3NH3PbI3 unveiled by pump-push-probe spectroscopy

Halide perovskites are promising materials for development in hot carrier (HC) solar cells, where the excess energy of above-bandgap photons is harvested before being wasted as heat to enhance device efficiency. Presently, HC separation and transfer processes at higher-energy states remain poorly understood. Here, we investigate the excited state dynamics in CH3NH3PbI3 using pump-push-probe spectroscopy. It has its intrinsic advantages for studying these dynamics over conventional transient spectroscopy, albeit complementary to one another. By exploiting the broad excited-state absorption characteristics, our findings reveal the transfer of HCs from these higher-energy states into bathophenanthroline (bphen), an energy selective organic acceptor far above perovskite's band edges. Complete HC extraction is realized only after overcoming the interfacial barrier formed at the heterojunction, estimated to be between 1.01 and 1.08 eV above bphen's lowest unoccupied molecular orbital level. The insights gained here are essential for the development of a new class of optoelectronics

Highly Efficient Thermally Co-evaporated Perovskite Solar Cells and Mini-modules

The rapid improvement in the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has prompted interest in bringing the technology toward commercialization. Capitalizing on existing industrial processes facilitates the transition from laboratory to production lines. In this work, we prove the scalability of thermally co-evaporated MAPbI3 layers in PSCs and mini-modules. With a combined strategy of active layer engineering, interfacial optimization, surface treatments, and light management, we demonstrate PSCs (0.16 cm2 active area) and mini-modules (21 cm2 active area) achieving record PCEs of 20.28% and 18.13%, respectively. Un-encapsulated PSCs retained ∼90% of their initial PCE under continuous illumination at 1 sun, without sample cooling, for more than 100 h. Looking toward tandem and building integrated photovoltaic applications, we have demonstrated semi-transparent mini-modules and colored PSCs with consistent PCEs of ∼16% for a set of visible colors. Our work demonstrates the compatibility of perovskite technology with industrial processes and its potential for next-generation photovoltaics

Fabrication and characterization of nanostructured optical interconnect devices

Optical communication is one of the most important areas of research in the field of micro & opto-electronics, owing to the ever-increasing demand for bandwidth to enable a future with high-speed voice, video, and data system for homebuyers. Cost effective solutions and reliability of the optical modules pose significant challenges for the adoption of the optical technology on local area network. One of the major areas that the project focused on was the use of polymer based technologies for packaging of optical transceiver assemblies and to integrate polymeric waveguides and plasmonic resonance based devices into these devices. The project successfully determined the materials needed and the methodologies needed to maximise optical efficiency losses in these optical subassemblies. Novel methodologies to characterise time, temperature, and environment (humidity) based optical properties and to incorporate them into appropriate models were also developed.RG 15/0

Development of portable organic thin film transistor (OTFT) breath analyzer for detection of NO, CO and H2S

Analysis of breath is feasible and could provide a non-invasive method for early detection, continuous monitoring and management of lung injury/diseases caused by battlefield trauma and infectious/chronic illness. Currently, clinical measurement of nitric oxide NO in exhaled air is proving to be a reliable marker of lung inflammation and oxidative stress. However, current detector systems are expensive, benchtop system and only detect a single analyte. Recently, several other volatile gases, such as carbon monoxide CO and ammonia NH3 have been detected and correlated with various types of pulmonary injury/disease.RG 110/0