• Energy Research

Organo-lead-halide perovskite based solar cells have achieved remarkable advancements in power conversion efficiencies (PCEs) in recent years. Given their attractive properties, possible applications for perovskites are wide ranging and among others, particularly appealing for building integrated photovoltaics (BIPVs). In this study, patterned perovskite films were successfully fabricated based on a microsphere lithography SiO2 honeycomb scaffold template, which was derived by a combination of air-water interface self-assembly and O2 plasma etching. These patterned perovskite films exhibited near-neutral-color and tunable semitransparency, which meet the requisites of semitransparent solar cells for BIPVs application. O2 plasma etching of the microsphere template could effectively improve the active layer average visible transmission (AVT), and the existence of the SiO2 nanoscaffold effectively smoothed the internal trade-off of active layer AVT and device PCE. Solar cell devices fabricated with these optimized patterened perovskite films yielded a maximum PCE of 10.3% with relatively high active layer AVT of 38%. This nanoscaffold patterned perovskite opens up a new strategy for design and fabrication of functional photoelectric device based on organo-lead-halide perovskite.

Herein we describe both theoretically and experimentally the optical response of solution-processed organic-inorganic halide perovskite solar cells based on mesostructured scaffolds. We develop a rigorous theoretical model using a method based on the propagation of waves in layered media, which allows visualizing the way in which light is spatially distributed across the device and serves to quantify the fraction of light absorbed by each medium comprising the cell. The discrimination between productive and parasitic absorption yields an accurate determination of the internal quantum efficiency. State-of-the-art devices integrating mesoporous scaffolds infiltrated with perovskite are manufactured and characterized to support the calculations. This combined experimental and theoretical analysis provides a rational understanding of the optical behavior of perovskite cells and can be beneficial for the judicious design of devices with improved performance. Notably, our model justifies the presence of a solid perovskite capping layer in all of the highest efficiency perovskite solar cells based on thinner mesoporous scaffolds.

AbstractOrganic–inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced ‘brightening’ of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.

AbstractThe performance of perovskite photovoltaics is fundamentally impeded by the presence of undesirable defects that contribute to non-radiative losses within the devices. Although mitigating these losses has been extensively reported by numerous passivation strategies, a detailed understanding of loss origins within the devices remains elusive. Here, we demonstrate that the defect capturing probability estimated by the capture cross-section is decreased by varying the dielectric response, producing the dielectric screening effect in the perovskite. The resulting perovskites also show reduced surface recombination and a weaker electron-phonon coupling. All of these boost the power conversion efficiency to 22.3% for an inverted perovskite photovoltaic device with a high open-circuit voltage of 1.25 V and a low voltage deficit of 0.37 V (a bandgap ~1.62 eV). Our results provide not only an in-depth understanding of the carrier capture processes in perovskites, but also a promising pathway for realizing highly efficient devices via dielectric regulation.

This is the first report of using anatase TiO(2) nanosheets with exposed (001) facets in a high-efficiency PbS quantum dot/TiO(2) heterojunction solar cell. The TiO(2) nanosheets have higher conduction band, and surface energy compared to normal anatase (101) TiO(2) nanoparticles. This PbS QD/TiO(2) heterojunction solar cell produces power conversion efficiency of 4.7% which is one of the highest reported in literature.

AbstractMesoporous nanofibers (NFs) with a high surface area of 112 m2/g have been prepared by electrospinning technique. The structures of mesoporous NFs and regular NFs are characterized and compared through scanning electron microscope (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and selected area electron diffraction (SAED) studies. Using mesoporous TiO2 NFs as the photoelectrode, solid‐state dye‐sensitized solar cells (SDSCs) have been fabricated employing D131 as the sensitizer and P3HT as the hole transporting material to yield an energy conversion efficiency (η) of 1.82%. A Jsc of 3.979 mA cm−2 is obtained for mesoporous NF‐based devices, which is 3‐fold higher than that (0.973 mA cm−2) for regular NF‐based devices fabricated under the same condition (η = 0.42%). Incident photon‐to‐current conversion efficiency (IPCE) and dye‐desorption test demonstrate that the increase in Jsc is mainly due to greatly improved dye adsorption for mesoporous NFs as compared to that for regular NFs. In addition, intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) measurements indicate that the mesopores on NF surface have very minor effects on charge transport and collection. Initial aging test proves good stability of the fabricated devices, which indicates the promise of mesoporous NFs as photoelectrode for low‐cost SDSCs.