Perovskite CH3NH3PbI3–XClx Solar Cells. Experimental Study of Initial Degradation Kinetics and Fill Factor Spectral Dependence

The main drawback of the methylammonium lead halide perovskite solar cells is their degradation in ambient atmosphere. To investigate ambient-air-induced cell degradation, spec-tral dependencies of open-circuit voltage (VOC), fill factor (FF) and the power conversion effi-ciency (PCE) have been acquired (for the first time reported in literature). Our custom-made measurement system allowed us to perform measurements of the above-mentioned entities in situ directly in vacuum during and after thermal deposition of the elec-trode. We also studied how these parameters in vacuum changed after cell exposure to ambient air for 85 min (50 nm top electrode) and for 180 min (100 nm top Ag electrode). For fresh CH3NH3PbI3–xClx cell (never been in open air) with very high shunt resistance of 3·107 Ω·cm2 (with practically no shorts and therefore FF could be determined mainly by charge carrier recombination processes) we found that FF in vacuum increased along with an increase of the incident photon energy from 0.55 at 760 nm up to 0.82 at 400 nm. Hypothesis considering hot polaron participation in charge carrier photogeneration and recombination processes as well as another competing hypothesis were offered as possible explanations for the observed FF increase. The kinetics of short-circuit photocurrent EQE with a change in pressure was also inves-tigated. It was also shown that perovskite solar cell degradation could be noticeably reduced by increasing the top Ag electrode thickness to at least 100 nm, which could possibly facilitate the usual encapsulation process.---//---This work is licensed under a CC BY 4.0 license.Institute of Solid State Physics, University of Latvia as the Centre of Excellence has received funding from the European Union’s Horizon 2020 Framework Pro-gramme H2020-WIDESPREAD-01-2016-2017-Teaming Phase2 under grant agreement No. 739508, project CAMART

CH3NH3PbI3-XCl2 Perovskite Solar Cell Grown by Interdiffusion of Stacking Layers

Organometalic halide perovskites in last two years have emerged as new class of light absorbers that have demonstrated exceptional progress in solar cell performance [1]. To overcome pinholes problem in CH3NH3PbI3-xClx we have been used modified interdiffusion method [2]: on patterned ITO coated glass after cleaning it in chloroform, deionized water, acetone and 2-propanol in an ultrasonic bath for a 15 min each; aqueous PEDOT:PSS layer was spin coated at 8000 rpm for 50 s. After heating this layer at 140◦C for 30 min the mixture of PbI2 and PbCl2 (with molar ratio 3.4) dissolved in DMF and DMSO mixture with molar ratio 3 was spin coated at a rate 6000 rpm at 65◦C using 65◦C hot solution and was dried at 70◦C in argon atmosphere for 45 minutes. On top of this layer CH3NH3I solution in 2-propanol (40 mg/mL) was spin coated at a rate 6000 rpm at 65◦C. The obtained bilayer system was annealed in closed system at 107◦C for 1 h and additionally 1 h in argon atmosphere. After cooling to room temperature system was covered with PCBM dissolved in DCB (30 mg/mL) at a rate 2000 rpm for 60 s and annealed in argon atmosphere at 105◦C for 1 h, cooled down and put in vacuum chamber where 50 nm thick C60 layer and 60 nm thick Ag electrode were thermally evaporated at pressure 10-6 mbar. All photoelectric measurements have been made in the same homemade vacuum cryostat where electrode was deposited at p~5∙10-7 mbar without breaking the vacuum and moving the cell. The spectral dependences of short circuit photocurrent external quantum efficiency (EQE), fill factor (FF) and open circuit voltage (VOC) has been investigated in spectral range 370-900 nm, using synhro-detection technique and PC controlled data storage equipment