MoS2 Quantum Dot/Graphene Hybrids for Advanced Interface Engineering of a CH3 NH3 PbI3 Perovskite Solar Cell with an Efficiency of over 20%

ABSTRACT

Interface engineering of organic–inorganic halide perovskite solar cells (PSCs) plays a pivotal role in achieving high power conversion efficiency (PCE). In fact, the perovskite photoactive layer needs to work synergistically with the other functional components of the cell, such as charge transporting/active buffer layers and electrodes. In this context, graphene and related two-dimensional materials (GRMs) are promising candidates to tune “on demand” the interface properties of PSCs. In this work, we fully exploit the potential of GRMs by controlling the optoelectronic properties of molybdenum disulfide (MoS2) and reduced graphene oxide (RGO) hybrids both as hole transport layer (HTL) and active buffer layer (ABL) in mesoscopic methylammonium lead iodide (CH3NH3PbI3) perovskite (MAPbI3)-based PSCs. We show that zero-dimensional MoS2 quantum dots (MoS2 QDs), derived by liquid phase exfoliated MoS2flakes, provide both hole-extraction and electron-blocking properties. In fact, on one hand, intrinsic n-type doping-induced intraband gap states effectively extract the holes through an electron injection mechanism. On the other hand, quantum confinement effects increase the optical band gap of MoS2 (from 1.4 eV for the flakes to >3.2 eV for QDs), raising the minimum energy of its conduction band (from −4.3 eV for the flakes to −2.2 eV for QDs) above the one of the conduction band of MAPbI3 (between −3.7 and −4 eV) and hindering electron collection. The van der Waals hybridization of MoS2 QDs with functionalized reduced graphene oxide (f-RGO), obtained by chemical silanization-induced linkage between RGO and (3-mercaptopropyl)trimethoxysilane, is effective to homogenize the deposition of HTLs or ABLs onto the perovskite film, since the two-dimensional nature of RGO effectively plugs the pinholes of the MoS2 QD films. Our “graphene interface engineering” (GIE) strategy based on van der Waals MoS2 QD/graphene hybrids enables MAPbI3-based PSCs to achieve a PCE up to 20.12% (average PCE of 18.8%). The possibility to combine quantum and chemical effects into GIE, coupled with the recent success of graphene and GRMs as interfacial layer, represents a promising approach for the development of next-generation PSCs.

Leyla Najafi, Babak Taheri, Beatriz Martín-García, Sebastiano Bellani, Diego Di Girolamo, Antonio Agresti, Reinier Oropesa-Nuñez, Sara Pescetelli, Luigi Vesce, Emanuele Calabrò, Mirko Prato, Antonio E. Del Rio Castillo, Aldo Di Carlo, Francesco Bonaccorso

DOI: 10.1021/acsnano.8b05514

ACS Publications
Publication Date (Web): September 21, 2018

https://pubs.acs.org/doi/10.1021/acsnano.8b05514

NEW ARCHITECTURE OF POLYMERIC CELLS WITH DNA AS A CONSTITUENT LAYER

A new architecture of polymeric cells that foresees the presence of DNA as a constituent layer: it is the result of the study conducted jointly by the new ultrafast spectroscopy laboratory of the Institute "Struttura della Materia" of CNR (Cnr-Ism) and the researchers of the Department of Engineering Electronics of the University of Rome "Tor Vergata" and of CHOSE.

The results of the research are published in Advanced Functional Materials (No. 28 of 27 June 2018):

https://www.cnr.it/it/news/8196/cnr-ism-e-universita-di-tor-vergata-svelano-come-il-dna-puo-migliorare-le-prestazioni-di-celle-fotovoltaiche-di-nuova-generazione

The complete article can be found at link:

https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201707126

LOW TEMPERATURE, SOLUTION-PROCESSED PEROVSKITE SOLAR CELLS AND MODULES WITH AN APERTURE AREA EFFICIENCY OF 11%

ABSTRACT

Planar perovskite solar cells and modules were realized by using low temperature solution-process fabrication procedures. The photovoltaic performance was improved by optimizing a SnO2 electron transport layer and its interface with the perovskite layer. We achieved a power conversion efficiency (PCE) of 17.3% on small area cell (0.09 cm2) with negligible hysteresis and a steady-state PCE equal to 17.4%. Furthermore, shelf life tests showed a relative decrease of only 5% in PCE from its initial value after 1000 h of storage in dark conditions in air (RH 20%). Up-scaling of the technology was implemented entirely in air with fabrication of modules with a high aperture ratio of 91%. The modules delivered a maximum PCE of 13.1% obtained on an active area of 13.8 cm2and of 11.9% on an aperture area of 15.2 cm2 representing state of art performance for fully low temperature solution processed planar perovskite solar modules.

Emanuele Calabrò, Fabio Matteocci, Alessandro Lorenzo Palma, Luigi Vesce, Babak Taheri, Laura Carlini, Igor Pis, Silvia Nappini, Janardan Dagar, Chiara Battocchio, Thomas M. Brown

DOI: 10.1016/j.solmat.2018.05.001

https://www.sciencedirect.com/science/article/pii/S0927024818302150

AGING EFFECTS IN INTERFACE-ENGINEERED PEROVSKITE SOLAR CELLS WITH 2D NANOMATERIALS: A DEPTH PROFILE ANALYSIS

ABSTRACT

The stability of perovskite solar cells (PSCs) is a major factor limiting the market breakthrough of this technology. To understand the aging effects in PSCs is mandatory to rationally design implemented architectures and materials combining a viable deposition process, efficiency and stability. Despite of this evidence, only few experimental works succeeded in the direct quantitative characterization of aging effects in PSCs. In this work, we apply state-of-the-art X-ray photoelectron spectroscopy (XPS) depth profile analysis and time-of-flight secondary ion mass spectrometry (ToF-SIMS) 3D imaging to investigate the light-induced degradation of layers and interfaces in reference (Au/Spiro-OMeTAD/CH3NH3PbI3/m-TiO2/cTiO2/FTO) and interface-engineered mesoscopic PSCs in which graphene flakes are added into the mesoscopic TiO2 layer and a solution-processed 2H-MoS2 flakes buffer layer is added at the Spiro-OMeTAD/CH3NH3PbI3interface. Results show that the graphene addition into the mesoscopic TiO2 layer improves the stability of the PSC by reducing the locally-inhomogeneous light-induced back-conversion of the CH3NH3PbI3 layer into PbIx and PbOx species and the consequent release of iodine species, which diffuse across the interfaces and causes the modifications at the gold electrode (Au-I bonding) and the mesoscopic TiO2 (Ti-I bonding) interfaces. Moreover, where the CH3NH3PbI3 layer is preserved the gold diffusion across the entire device structure is strongly reduced even after the aging. The 2H-MoS2 flakes buffer layer allows limiting the localized diffusion of gold and the iodine diffusion in as-prepared PSCs while it is rather ineffective in preventing light-induced aging effects. Overall, thanks to the lower average degradation of the layers and interfaces, interface engineered PSCs could retain ∼60% of their initial PCE after the aging respect to less than ∼25% in the reference cells.

Yan Busby, Antonio Agresti, Sara Pescetelli, Aldo Di Carlo, Celine Noel, Jean-Jacques Pireaux, Laurent Houssiau

DOI: 10.1016/j.mtener.2018.04.005

https://www.sciencedirect.com/science/article/pii/S2468606918300303

ENHANCED CHARGE SEPARATION EFFICIENCY IN DNA TEMPLATED POLYMER SOLAR CELLS

ABSTRACT

The insertion of a DNA nanolayer into polymer based solar cells, between the electron transport layer (ETL) and the active material, is proposed to improve the charge separation efficiency. Complete bulk heterojunction donor–acceptor solar cells of the layered type glass/electrode (indium tin oxide)/ETL/P3HT:PC70BM/hole transport layer/electrode (Ag) are investigated using femtosecond transient absorption spectroscopy both in the NIR and the UV–vis regions of the spectrum. The transient spectral changes indicate that when the DNA is deposited on the ZnO nanoparticles (ZnO‐NPs) it can imprint a different long range order on the poly(3‐hexylthiophene) (P3HT) polymer with respect to the non‐ZnO‐NPs/DNA containing cells. This leads to a larger delocalization of the initially formed exciton and its faster quenching which is attributed to more efficient exciton dissociation. Finally, the temporal response of the NIR absorption shows that the DNA promotes more efficient production of charge transfer states and free polarons in the P3HT cation indicating that the increased exciton dissociation correlates with increased charge separation.

Francesco Toschi, Daniele Catone, Patrick O'Keeffe, Alessandra Paladini, Stefano Turchini, Janardan Dagar, Thomas M. Brown

DOI: 10.1002/adfm.201707126

https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201707126

FACILE SYNTHESIS OF A SNO2@RGO NANOHYBRID AND OPTIMIZATION OF ITS METHANE-SENSING PARAMETERS

ABSTRACT

Stannic oxide nanoparticles and various compositions of SnO2@rGO (reduced graphene oxide) nanohybrids were synthesized by a facile hydrothermal method and utilized as chemiresistive methane gas sensors. To characterize the synthesized nanohybrids, BET (Brunauer-Emmett-Teller), XRD, FESEM, TEM, FTIR, and Raman techniques were used. Sensing elements were tested using a U-tube flow chamber with temperature control. To obtain the best sensor performance, i.e., the highest signal and the fastest response and recovery times, the sensing element composition, operating temperature, and gas flow rate were optimized. The highest response (change in resistance) of 47.6% for 1000 ± 5 ppm methane was obtained with the SnO2@rGO1% nanohybrid at 150 °C and a flow rate of 160 sccm; the response and recovery times were 61 s and 5 min, respectively. A sensing mechanism was suggested, based on the experiments.

Shiva Navazani, Ali Shokuhfar, Mostafa Hassanisadi, Mojtaba Askarieh, Aldo Di Carlo, Antonio Agresti

DOI: 10.1016/j.talanta.2018.01.015

https://www.sciencedirect.com/science/article/pii/S0039914018300213