Weidong Zhu

Efficient Bifacial Semitransparent Perovskite Solar Cells Using Ag/V2O5 as Transparent Anodes

Bifacial semitransparent inverted planar structured perovskite solar cells (PSCs) based on Cs0.05FA0.3MA0.7PbI2.51Br0.54 using an Ag thin film electrode and V2O5 optical coupling layer are investigated theoretically and experimentally. It is shown that the introduction of the cesium (Cs) ions in the perovskite could obviously improve the device performance and stability. When only the bare Ag film electrode is used, the PSCs show a bifacial performance with the power conversion efficiency (PCE) of 14.62% illuminated from the indium tin oxide (ITO) side and 5.45% from the Ag film side. By introducing a V2O5 optical coupling layer, the PCE is enhanced to 8.91% illuminated from the Ag film side, which is 63% improvement compared with the bare Ag film electrode, whereas the PCE illuminated from the ITO side remains almost unchanged. Moreover, when a back-reflector is employed, the PCE of device could be further improved to 15.39% by illumination from the ITO side and 12.44% by illumination from the Ag side. The devices also show superior semitransparent properties and exhibit negligible photocurrent hysteresis, irrespective of the side from which the light is illuminated. In short, the Ag/V2O5 double layer is a promising semitransparent electrode due to its low cost and simple preparation process, which also point to a new direction for the bifacial PSCs and tandem solar cells.

Intermediate Phase Intermolecular Exchange Triggered Defect Elimination in CH3NH3PbI3 toward Room-Temperature Fabrication of Efficient Perovskite Solar Cells

The solvent-engineered one-step spin-coating method has been widely used to produce full-coverage CH3NH3PbI3 films for perovskite solar cells by forming an intermediate phase. However, the resultant CH3NH3PbI3 films usually contain numerous structural and compositional defects mainly resulting from the fast crystallization of the intermediate phase as well as the escape of CH3NH3I species induced by the inevitably thermal annealing recipe. Herein, a facile room-temperature intermolecular exchange route is proposed to enable conversion of the intermediate phase into uniform and ultra-flat CH3NH3PbI3 films. It can effectively inhibit the formation of structural and compositional defects in the resultant films, and even repair their inherent defects. As a result, the efficiency of perovskite solar cells can be boosted to 19.45% with a stabilized value of 18.55%, which is much higher than that from the ones fabricated by thermal annealing. This study suggests a facile and low-cost route to room-temperature fabrication of highly efficient perovskite solar cells including flexible ones.

Improving Electron Extraction Ability and Device Stability of Perovskite Solar Cells Using a Compatible PCBM/AZO Electron Transporting Bilayer

Due to the low temperature fabrication process and reduced hysteresis effect, inverted p-i-n structured perovskite solar cells (PSCs) with the PEDOT:PSS as the hole transporting layer and PCBM as the electron transporting layer have attracted considerable attention. However, the energy barrier at the interface between the PCBM layer and the metal electrode, which is due to an energy level mismatch, limits the electron extraction ability. In this work, an inorganic aluminum-doped zinc oxide (AZO) interlayer is inserted between the PCBM layer and the metal electrode so that electrons can be collected efficiently by the electrode. It is shown that with the help of the PCBM/AZO bilayer, the power conversion efficiency of PSCs is significantly improved, with negligible hysteresis and improved device stability. The UPS measurement shows that the AZO interlayer can effectively decrease the energy offset between PCBM and the metal electrode. The steady state photoluminescence, time-resolved photoluminescence, transient photocurrent, and transient photovoltage measurements show that the PSCs with the AZO interlayer have a longer radiative carrier recombination lifetime and more efficient charge extraction efficiency. Moreover, the introduction of the AZO interlayer could protect the underlying perovskite, and thus, greatly improve device stability.

Efficient Semitransparent Perovskite Solar Cells Using a Transparent Silver Electrode and Four-Terminal Perovskite/Silicon Tandem Device Exploration

Four-terminal tandem solar cells employing a perovskite top cell and crystalline silicon (Si) bottom cell offer a simpler pathway to surpass the efficiency limit of market-leading single-junction silicon solar cells. To obtain cost-effective top cells, it is crucial to develop transparent conductive electrodes with low parasitic absorption and manufacturing cost. The commonly used indium tin oxide (ITO) shows some drawbacks, like the increasing prices and high-energy magnetron sputtering process. Transparent metal electrodes are promising candidates owing to the simple evaporation process, facile process conditions, and high conductivity, and the cheaper silver (Ag) electrode with lower parasitic absorption than gold may be the better choice. In this work, efficient semitransparent perovskite solar cells (PSCs) were firstly developed by adopting the composite cathode of an ultrathin Ag electrode at its percolation threshold thickness (11u2009nm), a molybdenum oxide optical coupling layer, and a bathocuproine interfacial layer. The resulting power conversion efficiency (PCE) is 13.38% when the PSC is illuminated from the ITO side and the PCE is 8.34% from the Ag side, and no obvious current hysteresis can be observed. Furthermore, by stacking an industrial Si bottom cell (PCEu2009=u200914.2%) to build a four-terminal architecture, the overall PCEs of 17.03% (ITO side) and 11.60% (Ag side) can be obtained, which are 27% and 39% higher, respectively, than those of the perovskite top cell. Also, the PCE of the tandem cell has exceeded that of the reference Si solar cell by about 20%. This work provides an outlook to fabricate high-performance solar cells via the cost-effective pathway.

Alleviating hysteresis and improving efficiency of MA1−yFAyPbI3−xBrx perovskite solar cells by controlling the halide composition

Due to their great potential for application in the future of photovoltaics, perovskite solar cells (PSCs) have attracted much attention recently. Changing the composition in perovskites is important for improving the performance of PSCs. In this work, PSCs with mixed MA/FA and Br/I components are fabricated. By changing the cation/anion composition, the MA0.7FA0.3Pb(I0.72Br0.18)3 PSC shows the negligible I–V hysteresis and the enhanced power conversion efficiency. And the statistics result also shows that devices with proper halide composition have a smaller discreteness in the device performance. We demonstrate that the halide ratio is essential for the formation of high-quality perovskite film with longer radiative carrier recombination lifetime, uniform crystal size, and better surface morphology. It is shown that the halide composition in the mixed PSCs could greatly affect the I–V hysteresis and power conversion efficiency (PCE). A proper Br ratio is important to help the device to alleviate the hysteresis and enhance PCE.