An encapsulation system comprising of a UV‐curable epoxy, a solution processed polymer interlayer, and a glass cover‐slip, is used to increase the stability of methylammonium lead triiodide (CH3NH3PbI3) perovskite planar inverted architecture photovoltaic (PV) devices. It is found this encapsulation system acts as an efficient barrier to extrinsic degradation processes (ingress of moisture and oxygen), and that the polymer acts as a barrier that protects the PV device from the epoxy before it is fully cured. This results in devices that maintain 80% of their initial power conversion efficiency after 1000 h of AM1.5 irradiation. Such devices are used as a benchmark and are compared with devices having initially enhanced efficiency as a result of a solvent annealing process. It is found that such solvent‐annealed devices undergo enhanced burn‐in and have a reduced long‐term efficiency, a result demonstrating that initially enhanced device efficiency does not necessarily result in long‐term stability.

We explore degradation pathways within encapsulated CH 3 NH 3 PbI 3-x Cl x perovskite devices based on the inverted architecture: ITO/PEDOT:PSS/CH 3 NH 3 PbI 3-x Cl x /PC 70 BM/LiF/Al. Devices were subjected to more than 670 h of continuous illumination approximating AM1.5, with a Ts80 lifetime of (280 ± 20) hours determined. Devices stored in the dark underwent a similar drop in efficiency over the same time-period. Using external quantum efficiency, time-resolved photoluminescence, X-ray diffraction, scanning electron microscopy and laser beam induced current mapping, we attribute the primary cause of degradation to reactions with residual moisture trapped in the device, resulting in the decomposition of the perovskite. 36

The addition of Hydrogen Iodide to organometal halide perovskite precursor solution at 1% by volume leads to a 10 significant enhancement in average power conversion efficiency (PCE) in inverted solar cell devices, increasing from 7.7% 11 to 11.9% and 6.1% to 10.0% in spin-cast and spray-cast devices respectively. We directly attribute this improved device 12 performance to increased thin-film surface coverage coupled with higher optical density. X-ray diffraction studies also 13 reveal that the HI additive facilitates full conversion of the precursor material to the crystalline perovskite phase. From 14 solution studies, we relate these changes in device performance to the presence and distribution of precursor aggregates 15 that effectively pattern the formation of perovskite crystals during film formation. 16

Perovskite solar cells utilising NiO and TiO2 charge-extraction layers, deposited via high-speed, low substrate-temperature reactive electron-beam evaporation, achieve 15.8% PCE.

An anionic conjugated polyelectrolyte poly[(9,9-bis(4-sulfonatobutyl sodium) fluorene-altphenylene)-ran-(4,7-di-2-thienyl-2,1,3-benzothiadiazole-alt-phenylene)] which exhibits good solubility in water was synthesised via Suzuki-cross coupling. This conjugated polyelectrolyte was used as an additive in the hole transporting layer within organic photovoltaic devices. There is an efficiency gain as a result of an improved carrier generation and charge transport across the interface into the hole transport layer when the work function of the hole transport later is well matched to the active layer of the solar cell. The best performances were achieved using 5 mg/ml of the polyelectrolyte additive added to the hole transport layer solution in which case the average power conversion efficiency increased from 4.63 % for reference devices without any additive to 5.26 % when the additive is present which is a 13 % improvement. The reproducibility of device performance was also significantly improved with the variation in fill factor, short circuit current and open circuit voltage all improving when the additive is present.