Stefano Razza

Solid-state solar modules based on mesoscopic organometal halide perovskite: a route towards the up-scaling process

We fabricated the first solid state modules based on organometal halide perovskite CH3NH3PbI3-xClx using Spiro-OMeTAD and poly(3-hexylthiophene) as hole transport materials. Device up-scaling was performed using innovative procedures to realize large-area cells and the integrated series-interconnections. The perovskite-based modules show a maximum conversion efficiency of 5.1% using both poly(3-hexylthiophene) and Spiro-OMeTAD. A long-term stability test was performed (in air, under AM1.5G, 1 Sun illumination conditions) using both materials showing different behaviour under continuous light stress. Whilst the poly(3-hexylthiophene)-based module efficiency drops by about 80% with respect to the initial value after 170 hours, the Spiro-based module shows a promising long-term stability maintaining more than 60% of its initial efficiency after 335 hours.

Vertical TiO2 Nanorods as a Medium for Stable and High-Efficiency Perovskite Solar Modules

Perovskite solar cells employing CH3NH3PbI3-xClx active layers show power conversion efficiency (PCE) as high as 20% in single cells and 13% in large area modules. However, their operational stability has often been limited due to degradation of the CH3NH3PbI3-xClx active layer. Here, we report a perovskite solar module (PSM, best and av. PCE 10.5 and 8.1%), employing solution-grown TiO2 nanorods (NRs) as the electron transport layer, which showed an increase in performance (∼5%) even after shelf-life investigation for 2500 h. A crucial issue on the module fabrication was the patterning of the TiO2 NRs, which was solved by interfacial engineering during the growth process and using an optimized laser pulse for patterning. A shelf-life comparison with PSMs built on TiO2 nanoparticles (NPs, best and av. PCE 7.9 and 5.5%) of similar thickness and on a compact TiO2 layer (CL, best and av. PCE 5.8 and 4.9%) shows, in contrast to that observed for NR PSMs, that PCE in NPs and CL PSMs dropped by ∼50 and ∼90%, respectively. This is due to the fact that the CH3NH3PbI3-xClx active layer shows superior phase stability when incorporated in devices with TiO2 NR scaffolds.

Research Update: Large-area deposition, coating, printing, and processing techniques for the upscaling of perovskite solar cell technology

To bring perovskite solar cells to the industrial world, performance must be maintained at the photovoltaic module scale. Here we present large-area manufacturing and processing options applicable to large-area cells and modules. Printing and coating techniques, such as blade coating, slot-die coating, spray coating, screen printing, inkjet printing, and gravure printing (as alternatives to spin coating), as well as vacuum or vapor based deposition and laser patterning techniques are being developed for an effective scale-up of the technology. The latter also enables the manufacture of solar modules on flexible substrates, an option beneficial for many applications and for roll-to-roll production.

Mesoscopic perovskite solar cells and modules

In this work we exploit the use of a new promising class of light harvesting materials, namely the hybrid organic halide perovskites (CH3NH3PbI3-xClx), for the fabrication of mesoscopic perovskite solar cells and series-connected monolithic perovskite module. To achieve this goal, important innovative procedures were implemented in order to define a reproducible fabrication path applicable also to large area devices. Small area solar cells were fabricated with both Spiro-OMeTAD and the P3HT polymer as Hole Transporting Material (HTM) both showing a Power Conversion Efficiency (PCE) up to 10.5%. First attempts to scale up the size of the cell to a module size shown a PCE of 5.1% on an active area of 13.44cm2. In order to improve the efficiency of the module, we developed a new Laser assisted patterning of the perovskite/compact layers together with an optimized perovskite deposition in controlled atmosphere. This allowed us to improve the module PCE up to 7.3% which represent the state of art efficiency for a perovskite module. A promising long-term stability was obtained for the module with Spiro-OMeTAD as HTM. Supporting simulations of Mesoscopic Perovskite Solar Cells were obtained by using the multiscale device simulator TiberCAD.

Perovskite and a-Si:H/c-Si tandem solar cell

In this work the fabrication of Perovskite/Si tandem-solar cell is reported and discussed. In principle this configuration allows cell efficiency higher than single c-Si junction. While Perovskite cell was used as top cell, a-Si:H/c-Si heterojunction was adopted as a bottom cell. The investigated process starts from Glass/FTO/c-TiO2/n-TiO2/CH3NH3PbI3/ Spiro-OMeTAD/ITO top cell, coupled to an ITO/a-Si:H/c-Si/back reflector/Al heterojunction bottom cell. ITO film is used to join the top and bottom cell. Preliminary results demonstrate the feasibility of the tandem cell, indeed Voc value as high as 1.65mV has been achieved. Numerical simulations is used to evaluate the limit and the potentiality of the proposed tandem structure.

Device architectures with nanocrystalline mesoporous scaffolds and thin compact layers for flexible perovskite solar cells and modules

Hybrid organometallic halide perovskite photovoltaics has seen remarkable growth in world wide research and power conversion efficiencies (PCEs) over the last two years. Key advantages of perovskites devices, together with high PCEs typical of inorganic semiconductors, are represented by the ease of deposition of the precursors of the perovskite (via ink solutions) and their low temperature processing (<; 140°C), more typical of organic semiconductors. These values enable coating the active layers on plastic substrates, which can make the technology compatible with continuous roll to roll manufacturing. Flexible photovoltaics is drawing strong interest as it can also bring advantages to applications where flexibility, conformability, and being lightweight and easy-to-integrate are sought. Development of the technology on flexible substrates is far from trivial. Especially important is identifying materials and techniques that are low-temperature and compatible with plastic films even for the other components of the cell like the nanometer-thin electron extraction/blocking layers and the mesoporous nanocrystalline scaffolds. We will present effective strategies and formulations that enable the realization of efficient flexible perovskite cells and the first ever CH3NH3PbI3-xClx perovskite module on plastic film.