The diode behavior of photovoltaic devices based on methylammonium lead iodide (MAPbI3) perovskites is examined, in combination with electroluminescence measurements. From this analysis the diode ...ideality factors are extracted, which indicate that non‐radiative trap‐assisted recombination is the dominant recombination pathway, primarily caused by the presence of electron traps.
Hybrid lead halide perovskites are promising materials for future photovoltaics applications. Their spectral response can be readily tuned by controlling the halide composition, while their stability ...is strongly dependent on the film morphology and on the type of organic cation used. Mixed cation and mixed halide systems have led to the most efficient and stable perovskite solar cells reported, so far they are prepared exclusively by solution‐processing. This might be due to the technical difficulties associated with the vacuum deposition from multiple thermal sources, requiring a high level of control over the deposition rate of each precursor during the film formation. In this report, thermal vacuum deposition with multiple sources (3 and 4) is used to prepare for the first time, multications/anions perovskite compounds. These thin‐film absorbers are implemented into fully vacuum deposited solar cells using doped organic semiconductors. A maximum power conversion efficiency of 16% is obtained, with promising device stability. The importance of the control over the film morphology is highlighted, which differs substantially when these compounds are vacuum processed. Avenues to improve the morphology and hence the performance of fully vacuum processed multications/anions perovskite solar cells are proposed.
Multiple‐source (up to 4) thermal vacuum deposition is used to prepare for the first time multications/anions perovskite compounds. These thin‐film absorbers are implemented into fully vacuum deposited solar cells using doped organic semiconductors. A maximum power conversion efficiency of 16% is obtained, with promising device stability.
Trap-assisted recombination, despite being lower as compared with traditional inorganic solar cells, is still the dominant recombination mechanism in perovskite solar cells (PSCs) and limits their ...efficiency. We investigate the attributes of the primary trap-assisted recombination channels (grain boundaries and interfaces) and their correlation to defect ions in PSCs. We achieve this by using a validated device model to fit the simulations to the experimental data of efficient vacuum-deposited p–i–n and n–i–p CH3NH3PbI3 solar cells, including the light intensity dependence of the open-circuit voltage and fill factor. We find that, despite the presence of traps at interfaces and grain boundaries (GBs), their neutral (when filled with photogenerated charges) disposition along with the long-lived nature of holes leads to the high performance of PSCs. The sign of the traps (when filled) is of little importance in efficient solar cells with compact morphologies (fused GBs, low trap density). On the other hand, solar cells with noncompact morphologies (open GBs, high trap density) are sensitive to the sign of the traps and hence to the cell preparation methods. Even in the presence of traps at GBs, trap-assisted recombination at interfaces (between the transport layers and the perovskite) is the dominant loss mechanism. We find a direct correlation between the density of traps, the density of mobile ionic defects, and the degree of hysteresis observed in the current–voltage (J–V) characteristics. The presence of defect states or mobile ions not only limits the device performance but also plays a role in the J–V hysteresis.
Efficient monolithic perovskite/perovskite tandem solar cells are fabricated using two perovskite absorbers with complementary bandgaps. By employing doped organic semiconductors, an efficient and ...selective extraction of the charge carriers is ensured. This study demonstrates perovskite/perovskite tandem cells delivering a maximum efficiency of 18%, highlighting the potential of vacuum‐deposited multilayer structures in overcoming the efficiency of single‐junction perovskite devices.
To improve the efficiency of existing perovskite solar cells (PSCs), a detailed understanding of the underlying device physics during their operation is essential. Here, a device model has been ...developed and validated that describes the operation of PSCs and quantitatively explains the role of contacts, the electron and hole transport layers, charge generation, drift and diffusion of charge carriers and recombination. The simulation to the experimental data of vacuum‐deposited CH3NH3PbI3 solar cells over multiple thicknesses has been fit and the device behavior under different operating conditions has been studied to delineate the influence of the external bias, charge‐carrier mobilities, energetic barriers for charge injection/extraction and, different recombination channels on the solar cell performance. By doing so, a unique set of material parameters and physical processes that describe these solar cells is identified. Trap‐assisted recombination at material interfaces is the dominant recombination channel limiting device performance and passivation of traps increases the power conversion efficiency (PCE) of these devices by 40%. Finally, guidelines to increase their performance have been issued and it is shown that a PCE beyond 25% is within reach.
A numerical model is developed and validated that describes the operation of perovskite solar cells and quantitatively explains the role of contacts, the charge transport layers, charge generation, drift and diffusion of carriers and recombination. By doing so, a unique set of material parameters and physical processes is identified that describes these solar cells. To increase their performance, some guidelines are issued.
The synthesis of three enamine hole‐transporting materials (HTMs) based on Tröger's base scaffold are reported. These compounds are obtained in a three‐step facile synthesis from commercially ...available materials without the need of expensive catalysts, inert conditions or time‐consuming purification steps. The best performing material, HTM3, demonstrated 18.62 % PCE in PSCs, rivaling spiro‐OMeTAD in efficiency, and showing markedly superior long‐term stability in non‐encapsulated devices. In dopant‐free PSCs, HTM3 outperformed spiro‐OMeTAD by a factror of 1.6. The high glass‐transition temperature (Tg=176 °C) of HTM3 also suggests promising perspectives in device applications.
Three enamine hole‐transporting materials (HTMs) based on Tröger's base scaffold were synthesized. These compounds are obtained in a three‐step facile synthesis from commercially available materials without the need of expensive catalysts, inert conditions or time‐consuming purification steps.
A series of bis-cyclometalated iridium(III) complexes of general formula Ir(ppy)2(N∧N)PF6 (ppy– = 2-phenylpyridinate; N∧N = 2-(1H-imidazol-2-yl)pyridine (1), 2-(2-pyridyl)benzimidazole (2), ...1-methyl-2-pyridin-2-yl-1H-benzimidazole (3), 2-(4′-thiazolyl)benzimidazole (4), 1-methyl-2-(4′-thiazolyl)benzimidazole (5)) is reported, and their use as electroluminescent materials in light-emitting electrochemical cell (LEC) devices is investigated. 2PF6 and 3PF6 are orange emitters with intense unstructured emission around 590 nm in acetonitrile solution. 1PF6, 4PF6, and 5PF6 are green weak emitters with structured emission bands peaking around 500 nm. The different photophysical properties are due to the effect that the chemical structure of the ancillary ligand has on the nature of the emitting triplet state. Whereas the benzimidazole unit stabilizes the LUMO and gives rise to a 3MLCT/3LLCT emitting triplet in 2PF6 and 3PF6, the presence of the thiazolyl ring produces the opposite effect in 4PF6 and 5PF6 and the emitting state has a predominant 3LC character. Complexes with 3MLCT/3LLCT emitting triplets give rise to LEC devices with luminance values 1 order higher than those of complexes with 3LC emitting states. Protecting the imidazole N–H bond with a methyl group, as in complexes 3PF6 and 5PF6, shows that the emissive properties become more stable. 3PF6 leads to outstanding LECs with simultaneously high luminance (904 cd m–2), efficiency (9.15 cd A–1), and stability (lifetime over 2500 h).
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