Cristina Roldán-Carmona

One-Year stable perovskite solar cells by 2D/3D interface engineering

Despite the impressive photovoltaic performances with power conversion efficiency beyond 22%, perovskite solar cells are poorly stable under operation, failing by far the market requirements. Various technological approaches have been proposed to overcome the instability problem, which, while delivering appreciable incremental improvements, are still far from a market-proof solution. Here we show one-year stable perovskite devices by engineering an ultra-stable 2D/3D (HOOC(CH2)4NH3)2PbI4/CH3NH3PbI3 perovskite junction. The 2D/3D forms an exceptional gradually-organized multi-dimensional interface that yields up to 12.9% efficiency in a carbon-based architecture, and 14.6% in standard mesoporous solar cells. To demonstrate the up-scale potential of our technology, we fabricate 10 × 10 cm2 solar modules by a fully printable industrial-scale process, delivering 11.2% efficiency stable for >10,000 h with zero loss in performances measured under controlled standard conditions. This innovative stable and low-cost architecture will enable the timely commercialization of perovskite solar cells.

Flexible high efficiency perovskite solar cells

Flexible perovskite based solar cells with power conversion efficiencies of 7% have been prepared on PET based conductive substrates. Extended bending of the devices does not deteriorate their performance demonstrating their suitability for roll to roll processing.

High efficiency methylammonium lead triiodide perovskite solar cells: the relevance of non-stoichiometric precursors

Methylammonium lead iodide perovskite solar cells with improved performance and stability have been successfully prepared by using a non-stoichiometric PbI2 : CH3NH3I ratio in the precursor solution, and yield a power conversion efficiency (PCE) of above 19% under 1 sun for the champion cell.

High efficiency single-junction semitransparent perovskite solar cells

Semitransparent perovskite solar cells with a high power conversion efficiency (PCE) above 6% and 30% full device transparency have been achieved by implementing a thin perovskite layer and a simple foil compatible layout.

Highly efficient perovskite solar cells with a compositionally engineered perovskite/hole transporting material interface

Perovskite solar cells (PSCs) have experienced an outstanding advance in power conversion efficiency (PCE) by optimizing the perovskite layer morphology, composition, interfaces, and charge collection efficiency. To enhance PCE, here we developed a new method i.e., engineering a compositional gradient thinly at the rear interface between the perovskite and the hole transporting materials. We demonstrate that charge collection is improved and charge recombination is reduced by formation of an engineered passivating layer, which leads to a striking enhancement in open-circuit voltage (VOC). The passivation effect induced by constructing an additional FAPbBr3−xIx layer on top of the primary (FAPbI3)0.85(MAPbBr3)0.15 film was proven to function as an electron blocking layer within the perovskite film, resulting in a final PCE of 21.3%. Our results shed light on the importance of the interfacial engineering on the rear surface of perovskite layers and describe an innovative approach that will further boost the PSC efficiency.

Benzotrithiophene-Based Hole-Transporting Materials for 18.2% Perovskite Solar Cells

New star-shaped benzotrithiophene (BTT)-based hole-transporting materials (HTM) BTT-1, BTT-2 and BTT-3 have been obtained through a facile synthetic route by crosslinking triarylamine-based donor groups with a benzotrithiophene (BTT) core. The BTT HTMs were tested on solution-processed lead trihalide perovskite-based solar cells. Power conversion efficiencies in the range of 16 % to 18.2 % were achieved under AM 1.5 sun with the three derivatives. These values are comparable to those obtained with todays most commonly used HTM spiro-OMeTAD, which point them out as promising candidates to be used as readily available and cost-effective alternatives in perovskite solar cells (PSCs).

Efficient methylammonium lead iodide perovskite solar cells with active layers from 300 to 900 nm

Efficient methylammonium lead iodide perovskite-based solar cells have been prepared in which the perovskite layer is sandwiched in between two organic charge transporting layers that block holes and electrons, respectively. This configuration leads to stable and reproducible devices that do not suffer from strong hysteresis effects and when optimized lead to efficiencies close to 15%. The perovskite layer is formed by using a dual-source thermal evaporation method, whereas the organic layers are processed from solution. The dual-source thermal evaporation method leads to smooth films and allows for high precision thickness variations. Devices were prepared with perovskite layer thicknesses ranging from 160 to 900 nm. The short-circuit current observed for these devices increased with increasing perovskite layer thickness. The main parameter that decreases with increasing perovskite layer thickness is the fill factor and as a result optimum device performance is obtained for perovskite layer thickness aro...

Pulsed-current versus constant-voltage light-emitting electrochemical cells with trifluoromethyl-substituted cationic iridium(III) complexes

We report on five cationic iridium(III) complexes with cyclometalating 2-(3′-trifluoromethylphenyl)pyridine and a diimine, [(C⁁N)2Ir(N⁁N)](PF6), N⁁N = 4,4′-R2-2,2′-dipyridyl or 4,7-R2-1,10-phenanthroline (R = H, Me, tert-Bu, Ph), and characterize three of them by crystal structure analysis. The complexes undergo oxidation of the Ir–aryl fragment at 1.13–1.16 V (against ferrocene couple) and reduction of the N⁁N ligand at −1.66 V to −1.86 V, and have a redox gap of 2.84–2.99 V. The complexes exhibit bluish-green to green-yellow phosphorescence in an argon-saturated dichloromethane solution at room temperature with a maximum at 486–520 nm, quantum yield of 61–67%, and an excited-state lifetime of 1.2–4.3 μs. In two-layer spin-coated light-emitting electrochemical cells (LEC) operated at a constant-voltage (4 V) or a pulsed-current (100 A m−2 per pulse; block wave, 1000 Hz; 50% duty), the complexes exhibit green-yellow electroluminescence with a maximum at 547–556 nm. The luminance and efficiency of LEC do not level off after peaking but decay; for example, the luminance of the devices after reaching the peak of 195–1094 cd m−2 halves in 9–580 min. The best of the new LEC runs under pulsed-current driving and exhibits peak efficiencies of 16.8 cd A−1 and 7.9 lm W−1 and an EQE of 5.4% at a luminance of ≥834 cd m−2. We find that the pulsed-current LEC offer the following advantages over the constant-voltage LEC: lower current, higher stability, faster turn-on, and higher efficiency at higher luminance.

Tuning the Emission of Cationic Iridium (III) Complexes Towards the Red Through Methoxy Substitution of the Cyclometalating Ligand

The synthesis, characterization and evaluation in solid-state devices of a series of 8 cationic iridium complexes bearing different numbers of methoxy groups on the cyclometallating ligands are reported. The optoelectronic characterization showed a dramatic red shift in the absorption and the emission and a reduction of the electrochemical gap of the complexes when a methoxy group was introduced para to the Ir-C bond. The addition of a second or third methoxy group did not lead to a significant further red shift in these spectra. Emission maxima over the series ranged from 595 to 730 nm. All complexes possessing a motif with a methoxy group at the 3-position of the cyclometalating ligands showed very short emission lifetimes and poor photoluminescence quantum yields whereas complexes having a methoxy group at the 4-position were slightly blue shifted compared to the unsubstituted parent complexes, resulting from the inductively electron withdrawing nature of this directing group on the Ir-C bond. Light-emitting electrochemical cells were fabricated and evaluated. These deep red emitters generally showed poor performance with electroluminescence mirroring photoluminescence. DFT calculations accurately modelled the observed photophysical and electrochemical behavior of the complexes and point to an emission from a mixed charge transfer state.

Dynamically Doped White Light Emitting Tandem Devices

Solution-processed, salt-containing, blue and orange light-emitting layers lead to efficient white light-emitting devices when arranged in a tandem configuration separated by a thin metal layer.