In this work, we report the benefits of incorporating p h e n e t h y l a m m o n i u m c a t i o n ( P E A + ) i n t o ( H C -(NH 2 ) 2 PbI 3 ) 0.85 (CH 3 NH 3 PbBr 3 ) 0.15 perovskite for the first time. After adding small amounts of PEA cation (<10%), the perovskite film morphology is changed but, most importantly, grain boundaries are passivated. This is supported by Kelvin Probe Force Microscopy (KPFM). The passivation results in the increase in photoluminescence intensity and carrier lifetimes of test structures and open-circuit voltages (V OC ) of the devices as long as the addition of PEA + is ≤4.5%. The presence of higher-band-gap quasi-2D PEA incorporated perovskite is responsible for the grain boundary passivation, and the quasi-2D perovskites are also found to be concentrated near the TiO 2 layer, revealed by PL spectroscopy. Results of moisture exposure tests show that PEA + incorporation is effective in slowing down the degradation of unencapsulated devices compared to the control devices without PEA + . These findings provide insights into the operation of perovskite solar cells when large cations are incorporated.

Layered low‐dimensional perovskite structures employing bulky organic ammonium cations have shown significant improvement on stability but poorer performance generally compared to their 3D counterparts. Here, a mixed passivation (MP) treatment is reported that uses a mixture of bulky organic ammonium iodide (iso‐butylammonium iodide, iBAI) and formammidinium iodide (FAI), enhancing both power conversion efficiency and stability. Through a combination of inactivation of the interfacial trap sites, characterized by photoluminescence measurement, and formation of an interfacial energetic barrier by which ionic transport is reduced, demonstrated by Kelvin probe force microscopy, MP treatment of the perovskite/hole transport layer interface significantly suppresses photocurrent hysteresis. Using this MP treatment, the champion mixed‐halide perovskite cell achieves a reverse scan and stabilized power conversion efficiency of 21.7%. Without encapsulation, the devices show excellent moisture stability, sustaining over 87% of the original performance after 38 d storage in ambient environment under 75 ± 20% relative humidity. This work shows that FAI/iBAI, is a new and promising material combination for passivating perovskite/selective‐contact interfaces.

aMonolithic perovskite/silicon tandem solar cells show great promise for further efficiency enhancement for current silicon photovoltaic technology. In general, an interface (tunnelling or recombination) layer is usually required for electrical contact between the top and the bottom cells, which incurs higher fabrication costs and parasitic absorption. Most of the monolithic perovskite/Si tandem cells demonstrated use a hetero-junction silicon (Si) solar cell as the bottom cell, on small areas only. This work is the first to successfully integrate a low temperature processed (r150 1C) planar CH 3 NH 3 PbI 3 perovskite solar cell on a homo-junction silicon solar cell to achieve a monolithic tandem without the use of an additional interface layer on large areas (4 and 16 cm 2 ).Solution processed SnO 2 has been effective in providing dual functions in the monolithic tandem, serving as an ETL for the perovskite cell and as a recombination contact with the n-type silicon homo-junction solar cell that has a boron doped p-type (p++) front emitter. The SnO 2 /p++ Si interface is characterised in this work and the dominant transport mechanism is simulated using Sentaurus technology computer-aided design (TCAD) modelling. The champion device on 4 cm 2 achieves a power conversion efficiency (PCE) of 21.0% under reverse-scanning with a V OC of 1.68 V, a J SC of 16.1 mA cm À2 and a high FF of 78% yielding a steady-state efficiency of 20.5%. As our monolithic tandem device does not rely on the SnO 2 for lateral conduction, which is managed by the p++ emitter, up scaling to large areas becomes relatively straightforward. On a large area of 16 cm 2 , a reverse scan PCE of 17.6% and a steady-state PCE of 17.1% are achieved. To our knowledge, these are the most efficient perovskite/homo-junction-silicon tandem solar cells that are larger than 1 cm 2 . Most importantly, our results demonstrate for the first time that monolithic perovskite/silicon tandem solar cells can be achieved with excellent performance without the need for an additional interface layer. This work is relevant to the commercialisation of efficient large-area perovskite/homo-junction silicon tandem solar cells. Broader contextA simple approach for integrating a perovskite solar cell monolithically onto a Si solar cell is reported here. The first advantage of this approach is that it does not require additional fabrication of an additional interface layer between the perovskite and Si cell. The second advantage of this approach is that it is compatible with a homo-junction p-n Si solar cell, which is a common Si solar cell structure for commercial cells. The third advantage is that the entire sequence for the planar perovskite cell fabrication is done at low temperatures, minimising damage to the bottom Si solar cell. The fourth advantage is that the SnO 2 electron transport layer of the perovskite top cell also serves as a recombination contact with the silicon bottom cell. Finally, this monolithic tandem approach does not rely on the SnO 2 for lateral conducti...

For the first time, we report large-area (16 cm2) independently certified efficient single perovskite solar cells (PSCs) by overcoming two challenges associated with large-area perovskite solar cells. The first challenge of realizing a homogeneous and densely packed perovskite film over a large area is overcome by using an antisolvent spraying process. The second challenge of removing the series resistance limitation of transparent conductor is overcome by incorporating a metal grid designed using a semidistributed diode model. A 16 cm2 perovskite solar device at the cell level rather than at the module level is demonstrated using the modified solution process in conjunction with the use of a metal grid. The cell is independently certified to be 12.1% efficient. This work paves the way toward highly efficient and large perovskite cells without single-junction perovskite solar cells and silicon–perovskite tandems.

Improving the quality of perovskite poly‐crystalline film is essential for the performance of associated solar cells approaching their theoretical limit efficiency. Pinholes, unwanted defects, and nonperovskite phase can be easily generated during film formation, hampering device performance and stability. Here, a simple method is introduced to prepare perovskite film with excellent optoelectronic property by using acetic acid (Ac) as an antisolvent to control perovskite crystallization. Results from a variety of characterizations suggest that the small amount of Ac not only reduces the perovskite film roughness and residual PbI2 but also generates a passivation effect from the electron‐rich carbonyl group (CO) in Ac. The best devices produce a PCE of 22.0% for Cs0.05FA0.80MA0.15Pb(I0.85Br0.15)3 and 23.0% for Cs0.05FA0.90MA0.05Pb(I0.95Br0.05)3 on 0.159 cm2 with negligible hysteresis. This further improves device stability producing a cell that maintained 96% of its initial efficiency after 2400 h storage in ambient environment (with controlled relative humidity (RH) <30%) without any encapsulation.

Initial improvement in power conversion efficiency (PCE) during ambient storage is often seen in perovskite solar cells (PSCs). In this work, we studied the origin of PCE enhancement by ambient storage on typical n-i-p PSCs. We found improvements in both fill factor and opencircuit voltage during the first two days of storage. By analyzing temperature and light intensity dependent VOC, we found that the charge recombination mechanism changed from surface-to A Self-archived copy in Kyoto University Research Information Repository https://repository.kulib.kyoto-u.ac.jp bulk-dominated due to defect passivation at the perovskite surface upon storage. In addition, we found that storage improves the conductivity and lowers the highest occupied molecular orbital level of the spiro-OMeTAD improving charge extraction. These results show that there are more than one factor causing the storage-induced-improvements in perovskite solar cells.

NiO x is as a promising hole transporting layer (HTL) for perovskite solar cells (PSCs) due to its good stability, large bandgap, and deep valence band. The use of NiO x as a HTL for “inverted” PSC as part of a monolithic silicon/perovskite tandem solar cell is also suitable when the processing temperature is suitably low. Solution-processed NiO x at low temperature for PSCs remains to be improved due to the relatively low short-circuit current density (J sc) and fill factor (FF) of reported devices. In this work, the use of Ag-doping is reported for solution-processed NiO x film at 300 °C for inverted planar PSCs. We have shown that Ag-doping has no negative effect on the optical transmittance and morphology of the NiO x film and the overlying perovskite film. In addition, Ag-doping is effective in improving conductivity, improving carrier extraction, and enhancing the p-type property of the NiO x film confirmed by electrical characterization, photoluminescence measurements, and ultraviolet photoelectron spectroscopy. These improvements result in better devices based on the ITO/Ag:NiO x /​CH3NH3PbI3/​PCBM/BCP/Ag structure with improved average FF (from 69% to 75%), enhanced average J SC (by 1.2 mA/cm2 absolute) and enhanced average V OC (by 29 mV absolute). The average efficiency of these devices is 16.3% while the best device achieves a PCE of 17.3% with negligible hysteresis and a stabilized efficiency of 17.1%. In comparison, devices that use undoped NiO x have an average efficiency of 13.5%. This work demonstrates that silver is a promising doping material for NiO x by a simple solution process for high-performance inverted PSCs and perovskite tandems.

UV-induced degradation and parasitic ultraviolet (UV) absorption by the “sun-facing” carrier transport layer in a perovskite cell hinders stability and electrical performance when the perovskite cell is a top cell for a Si-based tandem. In this work, we tackle these issues by applying textured polydimethylsiloxane (PDMS) films that incorporate a down-shifting material (Ba,Sr)2SiO4:Eu2+ micron phosphor on the front of monolithic perovskite/silicon tandem cells. This film serves multiple purposes: antireflective control for the top cell, light trapping in the Si cell, as well as absorbing UV and re-emitting green light with high quantum yield. When applied onto a 4 cm2 monolithic perovskite/silicon tandem solar cell, the power conversion efficiency was improved from 20.1% (baseline device without any antireflective film) to 22.3% (device with an antireflective film but without the phosphors) and to 23.1% (device with down-shifting phosphor-incorprated antireflective film). The steady-state efficiency of 23.0% and a high fill factor (FF) of 81% achieved by the champion device are the highest values to date for a monolithic perovskite/silicon tandem that uses a homojunction silicon bottom cell. Moreover, results of a continuous UV irradiation test show that this composite down-shifting antireflection film significantly enhances the UV stability for the tandem device. This work demonstrates an elegant approach for improving the efficiency and stability for larger-area perovskite/silicon tandems.