• Energy Research

AbstractStacking two photovoltaic (PV) cells to form a tandem structure can improve the efficiency of PV modules, and if achieved at sufficiently low cost, could dominate the PV market in the future. Rapid progress in silicon–perovskite tandem (SPT) cell efficiency has been made, so cost modelling is becoming important in analysing the commercial attractiveness of this approach. While previous cost modelling assumed idealised production processes, this work focuses first on six demonstrated SPT sequences using both homojunction and heterojunction bottom silicon cells, analysed in detail using a bottom‐up cost and uncertainty model and then compared with other reported SPT high‐efficiency cells. This identifies cost barriers in the perovskite cell, including high‐cost hole transport material (HTM) and electron transport layer (ETL) materials such as (2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene [SPIRO] and [6,6]‐phenyl‐C61‐butyric acid methyl ester [PCBM]), and the use of spin coating which has a high wastage rate. Once these cost issues are solved, the silicon cell cost becomes important, and the use of lower cost homojunction cells with p‐type wafers can further reduce costs. A hypothetical medium term low‐cost sequence that combines the lowest cost parts of the analysed sequences and an improved perovskite deposition process has a projected likely cost of $1.50/cell, which if combined with 25% efficiency would give a favourable levelised cost of electricity (LCOE) compared with industry standard c‐Si cells. This analysis guides research directions to address cost issues in parallel with higher efficiencies in this technology area.

A spin-coating-free fabrication sequence has been developed for the fabrication of highly efficient organic-inorganic halide perovskite solar cells (PSCs). A novel blow-drying method is demonstrated to be successful in depositing high quality mesoporous TiO2 (mp-TiO2), methylammonium lead halide (CH3NH3PbI3) perovskite and spiro-MeOTAD layers. When combined with compact TiO2 (c-TiO2) deposited by spray pyrolysis which is also a spin-coating-free process, a stabilized power conversion efficiency exceeding 17% can be achieved for the glass/FTO/c-TiO2/mp-TiO2/ CH3NH3PbI3/spiro-MeOTAD/Au device. This is the highest efficiency for PSCs fabricated without the use of spin-coating to our knowledge. This method provides a pathway towards a scalable process for fabricating high-performance, large area and reproducible PSCs.

A simple and scalable interface-layer free monolithic perovskite/silicon tandem has been demonstrated achieving over 20% efficiency on a large area.

An ultra-thin indium tin oxide interlayer design was developed for interfacing perovskite solar cells with Si solar cells thereby minimising shunting effects for large area monolithic tandem devices.

AbstractWe present a simple yet powerful analysis of Suns‐photoluminescence quantum yield measurements that can be used to determine the surface saturation current densities of thin film semiconductors. We apply the method to state‐of‐the‐art polycrystalline perovskite thin films of varying absorber thickness. We show that the non‐radiative bimolecular recombination in these samples originates from the surfaces. To the best of our knowledge, this is the first study to demonstrate and quantify non‐linear (bimolecular) surface recombination in perovskite thin films.

Abstract Organic-inorganic hybrid lead halide perovskite has shown to be one of the best light-harvesting materials for solar cell in the last decade. However, there still is needed a deeper understanding of phase and film formation for better control of device fabrication. In this work, we visualise the formation mechanism of Cs0.15(MA0.7FA0.3)0.85PbI3 perovskite by the sequential spin-coating method and how changes in the dispensing timing and substrate motion affect the formation process and properties of the final film quality. In particular, this is the first time that we are able to visualise and identify the different stages of the film formation: i) “initial formation”; ii) “perovskite deconstruction” and iii) “perovskite re-crystallisation”. This particularly applies to films that are sequentially spin-coated and involve the use of dimethyl sulfoxide (DMSO) as the “deconstruction” is caused by the formation of intermediate-DMSO-complex. These findings are validated by FTIR and XRD measurements. Comparison among processes also suggests that motion causes an earlier onset of deconstruction, which will lead to a slower re-crystallisation resulting in better quality perovskite film with less non-perovskite phase. This can be achieved by motion dispensing and dynamic processing (where there is no stoppage between the two sequential steps). Reasons for the earlier onset of deconstruction are the higher kinetic energy supplied by the dynamic process. This work has provided more insights into the complex stages involved in perovskite conversion specific to sequential processing. The knowledge will aid future process optimisation for better device fabrication.

AbstractImproving 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.