Efficient Mesoscopic Perovskite Solar Cells Research Articles

Enhancing the efficiency of perovskite solar cells by modifying perovskite layer with rGO additive

• Effective rGO additive combined with one-step deposition was used. • The prepared rGO-doped perovskite has better properties compared with undoped film. • Significant enhancement of perovskite solar cell (PSC) performance. Recently, Organometallic trihalide perovskites have been commonly studied owing to their outstanding optoelectronic characteristics. The current study uses reduced graphene (rGO) into perovskite solution as harvester layer for efficient mesoscopic perovskite solar cells (PSCs). We systematically investigated the impact of rGO additive on the optoelectronic performance properties of PSCs. The perovskite film with the rGO exhibited a dense and pinhole-free film with good crystalline nature. While, the devices without the rGO additive suffered from severe recombination process, which was investigated with photoluminescence (PL) spectroscopy. Consequently, the device with the rGO exhibited a power conversion efficiency (PCE) of 11.55%, together with an open voltage (Voc) of 0.934 V, a short current density (Jsc) of 17.67 mA/cm 2 and a fill-factor (FF) of 70%.

Efficient mesoscopic perovskite solar cells from emulsion-based bottom-up self-assembled TiO2 microspheres

Mesoscopic perovskite solar cells (PSCs) usually show superior photovoltaic performance to their planar counterparts because of the mesoporous electron transport layers (ETLs) benefiting for perovskite crystal growth and electron transport. However, the preparation of high-quality mesoporous ETLs needs selecting sizable semiconductor nanocrystals commonly within 20–50 nm, smaller or larger nanocrystals will lead to either too narrow pores to effectively infiltrate perovskite materials or too small surface area to efficiently extract charges from perovskite materials. Using sizable semiconductor microspheres can solve the issue, whereas it is also not easy to synthesis sizable semiconductor microspheres. Here, a novel emulsion-based bottom-up self-assembly strategy is used to prepare small size (about 150 nm) TiO2 microspheres from ultra-small (about 3.6 nm) TiO2 nanocrystals. The as-prepared mesoscopic PSCs can yield a champion PCE as high as 19.27% with a much smaller current–voltage hysteresis compared with those of the planar one. Specially, the emulsion-based bottom-up self-assembly strategy is a general way for preparing microspheres from wide kinds of semiconductor nanocrystals, so it will greatly expand the material selection range for preparing efficient mesoscopic PSCs and even inverted mesoscopic devices.

Spray-coated monodispersed SnO2 microsphere films as scaffold layers for efficient mesoscopic perovskite solar cells

Mesoporous SnO2 microspheres are a class of promising electron transport materials for mesoscopic perovskite solar cells, but a smooth and dense film as requested by electron transport layer is difficult to realize using the microspheres. Here, a series of monodispersed SnO2 microspheres with high specific surface area and good crystallinity are synthesized via a surfactant-free solvothermal method. These SnO2 microspheres showing small diameters of about 75, 110 and 200 nm with narrow size distribution are achieved by precisely controlling the crystal growth process. They are suitable for constructing the electron transport layers whose thickness is only about hundreds nanometers. Besides, as the microspheres easily slip off from the substrate during the conventional spin coating process, the spray coating method is exploited to prepare high quality electron transport layers. As a result, a power conversion efficiency of 16.85% is yielded by using the 75 nm sized SnO2 microspheres as the electron transport layers. This high power conversion efficiency is attributed to the fast electron transport and inhibited charge recombination. To further improve the charge transfer between the electron transport layer and perovskite layer, graphene quantum dots are added into the SnO2 microspheres, and a best efficiency of 17.08% is obtained.

HxMoO3−ynanobelts: an excellent alternative to carbon electrodes for high performance mesoscopic perovskite solar cells

The HxMoO3−ynanobelts as electrode has been firstly demonstrated with efficiency up to 14.5% in mesoscopic perovskite solar cells. This work thus opens up a new direction for developing electrode materials for more efficient mesoscopic perovskite solar cells.

Distinctive electroluminescence characteristics behind efficient mesoscopic perovskite solar cell

Abstract Metal halide perovskites are emerging as exceptional class of materials due to its unprecedented collective advantages for optoelectronic applications. Here, the efficient mesoscopic perovskite solar cells (M-PSCs) with the architecture of FTO-SnO2/m-TiO2 + MAPbI3/Spiro-OMeTAD/Ag were synthesized, where the discontinuous SnO2 derived blended-interfacial-layer worked as electron transport layer (ETL). A moderate power conversion efficiencies (PCEs) of 17.42% was achieved. Notably, a 10 s level ultra-long rise time in time-resolved electroluminescence (EL) characteristics was observed from the same device as the MAPbI3 perovskite layer served as light emitter. Such performance was attributed to the reasonable device design based on the dynamics favorable electron transport layer. This achievement would be beneficial for further understanding the working mechanism of perovskite-based optical-to-electrical and electrical-to-optical conversion devices.

Rational design of SnO2-based electron transport layer in mesoscopic perovskite solar cells: more kinetically favorable than traditional double-layer architecture

Here, the interfacial synergism of discontinuous spot shaped SnO2 and TiO2 mesoporous nanocomposite as electron transfer layer (ETL) underlayer is presented in highly efficient mesoscopic perovskite solar cells (M-PSCs). Based on this new strategy, strong charge recombination observed in previous SnO2-based ETLs is suppressed to a great extent as the pathways of charge recombination and energy loss are blocked effectively. Meanwhile, the internal series resistance of entire M-PSC is decreased remarkably. The new ETL is more kinetically favorable to electron transfer and thus results in significant photovoltaic improvement and alleviated hysteresis effect of M-PSCs.

Sequential multi-drop coating method for large crystallized α-(NH 2 ) 2 CHPbI 3 and mixed-organic-cation perovskite films for highly efficient mesoscopic perovskite solar cells

Abstract A simplified multi-drop coating method that improves the grain size and film quality is introduced to construct and stabilize a pure α-phase formamidinium (FA) lead iodide ((NH 2 ) 2 CHPbI 3 , FAPbI 3 ) perovskite layer. The developed method is then extended to fabricate an FA and methylammonium (MA) (FA/MA) mixed cation perovskite film under ambient conditions. The acquired FAPbI 3 film contains micron-sized large grains with preferred [111] orientation, which dramatically reduced the grain boundary area and the associated charge recombination to provide high short-circuit current densities and power conversion efficiencies (PCE) of up to 23.86 mA cm −2 and 17.66%, respectively. The open-circuit voltage of the device and the efficiency are further improved after extending this method to the FA/MA mixed perovskite film. Finally, the highest PCE reached 19.3%.

Novel spherical TiO2 aggregates with diameter of 100 nm for efficient mesoscopic perovskite solar cells

Abstract Novel monodispersed spherical TiO2 aggregate with a diameter of 100 nm (SP100), which is the smallest TiO2 spheres (or beads) reported thus far, has been prepared by a controlled hydrolysis and hydrothermal reaction. The obtained SP100 is a highly porous structure with an internal pore size of 12 nm and a surface area of 112 m2/g, and is shown to be an ideal building block of mesoporous TiO2 layer for CH3NH3PbI3–based perovskite solar cells (PSCs). The optimized PSC employing SP100 exhibits photovoltaic conversion efficiency of 18.41% with JSC of 22.91 mA/cm2, VOC of 1,049 mV and FF of 0.759. Furthermore, fabricated PSCs exhibit reproducible PCE values with little hysteresis in their J–V curves. Time-resolved photoluminescence measurement indicates that the PSC with SP100 (PSC-SP100), compared to the devices with the nanoparticles of 30 nm or 50 nm size shows notably faster electron injection from CH3NH3PbI3 to TiO2 layer, resulting from the extended contact area between perovskite and mesoporous TiO2 layer. Pulsed light-induced transient measurement of the photocurrent indicates that PSC-SP100 shows significantly longer electron lifetime, which is attributed to the suppression of electron recombination caused by the unique TiO2 network.

Synergistic effects of three-dimensional orchid-like TiO2 nanowire networks and plasmonic nanoparticles for highly efficient mesoscopic perovskite solar cells

A perovskite solar cell based on a collaborative scaffold structure consisting of orchid-like TiO2 nanowires (OC-TiO2 NWs) and silica-coated Ag@OC-TiO2 NWs exhibited the best power conversion efficiency of 15.09%.

Core-shell heterostructured metal oxide arrays enable superior light-harvesting and hysteresis-free mesoscopic perovskite solar cells.

To achieve highly efficient mesoscopic perovskite solar cells (PSCs), the structure and properties of an electron transport layer (ETL) or material (ETM) have been shown to be of supreme importance. Particularly, the core-shell heterostructured mesoscopic ETM architecture has been recognized as a successful electrode design, because of its large internal surface area, superior light-harvesting efficiency and its ability to achieve fast charge transport. Here we report the successful fabrication of a hysteresis-free, 15.3% efficient PSC using vertically aligned ZnO nanorod/TiO2 shell (ZNR/TS) core-shell heterostructured ETMs for the first time. We have also added a conjugated polyelectrolyte polymer into the growth solution to promote the growth of high aspect ratio (AR) ZNRs and substantially improve the infiltration of the perovskite light absorber into the ETM. The PSCs based on the as-synthesized core-shell ZnO/TiO2 heterostructured ETMs exhibited excellent performance enhancement credited to the superior light harvesting capability, larger surface area, prolonged charge-transport pathways and lower recombination rate. The unique ETM design together with minimal hysteresis introduces core-shell ZnO/TiO2 heterostructures as a promising mesoscopic electrode approach for the fabrication of efficient PSCs.