June 2018

Researchers at the University of Maryland (UMD) have identified the impact of the environment on perovskite materials. To understand the physical and chemical processes that lead to degradation, the team exposed these materials to various environmental factors in the lab and measured their response using a technique called 'in situ environmental photoluminescence (PL) to temporally and spectrally resolve the light emission within a loop of critical relative humidity (rH) levels.'

'We found that the humidity pathway determines the overall optical response of the perovskite materials, leading to a behavior called luminescence hysteresis, wherein the light emitted from the material depends not only on the current conditions but also the prior ones,' said the team. 'Further, we found that the amount of luminescence hysteresis is highly dependent on the ratio between two critical elements constituting the perovskites: Cs and Br.'

Oxford Photovoltaics has reported a new perovskite tandem solar cell record, certified by Fraunhofer ISE at a conversion efficiency of 27.3%. Oxford PV's latest record for a 1 cm² perovskite-silicon tandem solar, reportedly exceeds the 26.7% efficiency world record for a single-junction silicon solar cell.

Oxford PV recently produced a 1 cm² perovskite-silicon two-terminal tandem solar cell with a verified conversion efficiency of 25.2%, through an ongoing collaboration with Helmholtz-Zentrum Berlin (HZB) and the Photovoltaics and Optoelectronics Device Group at the University of Oxford, led by Professor Snaith.

Researchers from the universities of New York, Peking, Electronic Science and Technology of China, Yale and Johns Hopkins report they have solved a major challenge to the commercial production of perovskite solar cells, by turning to spray coating. The scientists say spraying can apply the electron transport layer (ETL) uniformly across a large area, and is suitable for manufacturing large solar panels and ensuring high performance.

The research team reported spray coating led to a 30% efficiency gain over other ETLs ' translating to a power conversion efficiency leap from 13% to over 17% ' and even resulted in fewer defects.

Oxford Photovoltaics, in collaboration with Helmholtz-Zentrum Berlin (HZB) and the Photovoltaics and Optoelectronics Device Group at the University of Oxford, produced a 1 cm² perovskite-silicon two-terminal tandem solar cell with a verified conversion efficiency of 25.2%. The two-terminal tandem solar cell efficiency was certified by the Fraunhofer Institute for Solar Energy Systems ISE.

Dr Chris Case, Chief Technology Officer at Oxford PV commented, 'The unique, optically enhanced architecture developed as part of this collaboration, minimizes losses, and has helped us achieve this record setting efficiency'.

Saudi Arabia-based Quantum Solutions demonstrated its perovskite quantum dots (with a focus on its green-colored ones) at SID Displayweek 2018, in addition to its Lead-Sulfide (PbS) QDs.

Quantum Solutions says it uses a flow reactor to create uniform and high-quality QDs at high yields and minimal waste. The company also develops encapsulation technology to protect the perovskite QDs. Their current materials have a lifetime of around 8,000 hours.

Researchers from Sungkyunkwan University recently reported the development of highly stable perovskite solar cells under extreme environments by improving passivation techniques.

The architecture of the solar cells has inverted planar devices (so-called p-i-n devices; light illumination through hole transport layers) with FTO/NiO/Perovskite/PCBM/AZO/Ag. AZO has been deposited via atmoic layer deposition method, which produces pinhole-free, uniform, and dense films. The AZO-deposited perovskite solar cells exhibited similar performances to the control solar cells due to negligible charge transporting retardation by the 3 orders of magnitude higher conductivity of AZO compared to that of PCBM. The ALD-grown AZO (ALD-AZO) layers also acted as dense, uniform, and impermeable passivation layers that prevented ingress of water into the perovskite films, egress of the volatile components of perovskite when heated, and interfacial degradation between the perovskite-PCBM heterojunction and the Ag electrode caused by unfavorable chemical reactions.

A KAIST research team has proposed a perovskite material, Cs2Au2I6 that serves as a potential active material for highly efficient lead-free thin-film photovoltaic devices. This material is expected to lay the foundation to overcome previously known limitations of perovskite including its stability and toxicity issues.

The joint team led by Professor Hyungjun Kim from the KAIST Department of Chemistry and Professor Min Seok Jang from the School of Electrical Engineering analyzed a previously discovered perovskite material, Cs2Au2I6, consisting of only inorganic substances and investigated its suitability for application in thin-film photovoltaic devices. Theoretical investigations suggests that this new perovskite material is not only as efficient but also more stable and environment friendly compared to the conventional perovskite materials.

Researchers from Rice University and Los Alamos National Laboratory have observed electronic properties of perovskites at the quantum scale, and made discoveries likely to impact the development of perovskite solar cells.

The team has developed a scale to determine the binding energy of excitons, and thus the bandgap structures, in perovskite wells. This scale, according to Rice University, could assist scientists in developing new semiconductor materials.

EPFL the CSEM PV-center researchers have combined silicon and perovskite to create solar cells with the resulting efficiency of 25.2%, in what is regarded as a record for this type of tandem cell. Their innovative yet simple manufacturing technique could be directly integrated into existing production lines, and efficiency could eventually rise above 30%.

The researchers explain that creating an effective tandem structure by superposing two materials is no easy task. "Silicon's surface consists of a series of pyramids measuring around 5 microns, which trap light and prevent it from being reflected. However, the surface texture makes it hard to deposit a homogeneous film of perovskite," explains Quentin Jeangros, who co-authored the paper. A common problem in such cells arises from the fact that when the perovskite is deposited in liquid form, it accumulates in the valleys between the pyramids while leaving the peaks uncovered, leading to short circuits. The team tackled this problem by using evaporation methods to form an inorganic base layer that fully covers the pyramids. That layer is porous, enabling it to retain the liquid organic solution that is then added using a thin-film deposition technique called spin-coating. The researchers subsequently heat the substrate to a relatively low temperature of 150°C to crystallize a homogeneous film of perovskite on top of the silicon pyramids.

China-based QD developer Zhijing Nanotech demonstrated its perovskite-QD film (PQDF) at Displayweek 2018. The company showcased a 55" LCD TV that uses the film to convert the blue LED color to a white background.

Zhijing Nanotech says that its low-cost PQDF can be used to achieve a high 110%+ NTSC color gamut and a high efficiency.