Perovskite solar cells have achieved photo-conversion efficiencies greater than 20%, making them a promising candidate as an emerging solar cell technology. While perovskite solar cells are expected to eventually compete with existing silicon-based solar cells on the market, their long-term stability has become a major bottleneck. In particular, perovskite films are found to be very sensitive to external factors such as air, UV light, light soaking, thermal stress and others. Among these stressors, light, oxygen and moisture-induced degradation can be slowed by integrating barrier or interface layers within the device architecture. However, the most representative perovskite absorber material, CH3NH3PbI3 (MAPbI3), appears to be thermally unstable even in an inert environment. This poses a substantial challenge for solar cell applications because device temperatures can be over 45 °C higher than ambient temperatures when operating under direct sunlight. Herein, recent advances in resolving thermal stability problems are highlighted through literature review. Moreover, the most recent and promising strategies for overcoming thermal degradation are also summarized.

Indigenous fire stewardship enhances ecosystem diversity, assists with the management of complex resources, and reduces wildfire risk by lessening fuel loads. Although Indigenous Peoples have maintained fire stewardship practices for millennia and continue to be keepers of fire knowledge, significant barriers exist for re-engaging in cultural burning. Indigenous communities in Canada have unique vulnerabilities to large and high-intensity wildfires as they are predominately located in remote, forested regions and lack financial support at federal and provincial levels to mitigate wildfire risk. Therefore, it is critical to uphold Indigenous expertise in leading effective and socially just fire stewardship. In this perspective, we demonstrate the benefits of cultural burning and identify five key barriers to advancing Indigenous fire stewardship in Canada. We also provide calls to action to assist with reducing preconceptions and misinformation and focus on creating space and respect for different knowledges and experiences. Despite growing concerns over wildfire risk and agency-stated intentions to establish Indigenous Peoples as partners in wildfire management, power imbalances still exist. The future and coexistence with fire in Canada needs to be a shared responsibility and led by Indigenous Peoples within their territories.

We explore a new characterization approach capable of probing the grain interior (GI) and grain boundary (GB) of a CHNHPbICl perovskite thin film. In particular, we have found that the photoluminescence (PL) spectrum observed for a CHNHPbICl perovskite thin film is asymmetric, and can be deconvoluted using a bi-Gaussian function, representing the ordered and disordered phases of the perovskite film. In order to understand the origin of the ordered and disordered phases of the perovskite film, two-dimensional (2D) PL mapping was performed to resolve the PL spectra at the nanoscale level. Quantitative analysis of the local PL spectra revealed that the ordered phase originated from the GIs while the disordered phase mainly came from the GBs. In particular, power-dependent PL measurements of the deconvoluted PL spectra revealed that smaller grained perovskites showed defect-mediated recombination at GBs but exciton-like transitions at GIs. In contrast, perovskite films with large grains followed an excellent power law, showing exciton-like recombination at both GIs and GBs. As expected, perovskite solar cells fabricated with large grains showed an increased efficiency with higher light absorption and higher charge extraction efficiency.

Carbon is inherently abundant in nature and relatively inexpensive, which can potentially reduce the manufacturing cost of solar cells. In recent years, carbon has been used as a hole transport layer or counter electrode in perovskite solar cells. Herein, we demonstrate that carbon can also be used as a charge transport layer capable of enhancing the energy conversion efficiency of a CHNHPbICl solar cell when carbon is combined with PCBM. Particularly, we have been able to deposit an ultra-flat carbon layer using an e-beam irradiation method, which exhibited much better conductivity than the competitive PCBM/C60 layer. In addition, quantitative analysis of interfacial charge dynamics shows that the quenching efficiency of PCBM/carbon is comparable to that of PCBM/C60 but better interface defect passivation and improved series and shunt resistances were observed when PCBM/carbon was employed. For the photovoltaic performance, the reference perovskite solar cell fabricated from the widely used PCBM/C60 has a power conversion efficiency (PCE) of 14% while the perovskite solar cell with PCBM/carbon has an increased PCE of 16%. Our results demonstrate the potential of the use of cost-effective carbon for perovskite solar cells, which could reduce production costs.

No abstract

a b s t r a c tGrain interiors (GIs) and grain boundaries (GBs) of perovskites have been investigated using chemically, spatially, and temporally resolved measurements. Two dimensional (2D) chemical mapping measurements revealed the GBs consisted of the non-stoichiometric PbI x or CH 3 NH 3 PbI x , that were characterized by an absence of chloride, an enriched oxygen concentration, and a high density of iodide vacancies. In addition, steady-state 2D photoluminescence showed the bandgap broadening at the GBs while 2D lifetime mapping measurement suggested that the GBs indeed contained deep defect centers. However, it is found that defective GBs in perovskite materials do not act as high recombination sites for photogenerated charge carriers due to the bandgap broadening of non-stoichiometric PbI x or CH 3 NH 3 PbI x perovskites at the GB that forms the potential barriers for photo-generated charge carriers toward the GBs. As a consequence, the photo-generated charge carriers adjacent to the GBs will be easily repelled by the GBs, resulting in a greater reduction of the recombination of photogenerated charge carriers. This is one possible reason for the high performance of CH 3 HN 3 PbI 3-x Cl x based solar cells.

The outgassing rates of three nominally identical 304L stainless steel vacuum chambers were measured to determine the effect of chamber coatings and heat treatments. One chamber was coated with titanium nitride (TiN) and one with amorphous silicon (a-Si) immediately following fabrication. The last chamber was first tested without any coating, and then coated with a-Si following a series of heat treatments. The outgassing rate of each chamber was measured at room temperatures between 15 and 30 °C following bakes at temperatures between 90 and 400 °C. Measurements for bare steel showed a significant reduction in the outgassing rate by nearly a factor of 20 after a 400 °C heat treatment-12 Torr L s -1 cm -2 prior to heat treatment, reduced to 1.7×10 -13 Torr L s -1 cm -2 following heat treatment). The chambers that were coated with a-Si showed minimal change in outgassing rates with heat treatment, though an outgassing rate reduced by heat treatments prior to a-Si coating was successfully preserved throughout a series of bakes.The TiN coated chamber exhibited remarkably low outgassing rates, up to four orders of magnitude lower than the uncoated stainless steel, but the uncertainty in these rates is 2 large due to the sensitivity limitations of the spinning rotor gauge accumulation measurement and the possibility of a small pump speed due to inhomogeneity in the TiN coating. The outgassing results are discussed in terms of diffusion-limited versus recombination-limited processes.3

No abstract