Progression towards high efficiency perovskite solar cells via optimisation of the front electrode and blocking layer

Abstract

The effects of a fluorine doped tin oxide (FTO) electrode, titanium dioxide (TiO 2Àx ) blocking layer (BL) and perovskite (methyl ammonium lead triiodide) preparation on the overall properties of the photovoltaic cells have been studied. The FTO electrode was deposited by atmospheric pressure chemical vapour deposition (APCVD) and the hole blocking layer by spin coating, atomic layer deposition (ALD) or sputtering. We have shown the importance of obtaining uniform thin films of FTO, with low sheet resistance to aid the formation of pin hole free uniform TiO 2Àx blocking layers and hence well adhered, perovskite layers. The optimal BL thickness was 20 nm, while thicker films gave decreased shunt resistance and thinner a greater number of pin holes through the layers. We also showed that the conformal nature of ALD and magnetron sputtering, along with their increased uniformity control over spin coating again improved cell efficiency. The main improvement comes for the smaller R oc , attributed to an improved electrical transport through particularly the sputtered TiO 2Àx blocking layer. After identifying the optimised parameters, all the properties were combined to fabricate large solar cells (1 cm 2 ) yielding power conversion efficiencies beyond 16%.

Roll to roll atmospheric pressure plasma enhanced CVD of titania as a step towards the realisation of large area perovskite solar cell technology

“…This is consistent also with the higher activation energy, which may indicate that these films have less oxygen deficiencies than the sputtered films. 38 This is consistent with the stoichiometric ratios determined by XPS, which showed TiO 1.82 for the four pass (40 nm) AP PECVD film compared to TiO 1.76 for the sputtered sample. However, deconvolution of the high resolution Ti 2p spectra showed a similar proportion of Ti 3+ at 3.21% and 3.37% for the AP PECVD and sputtered films respectively.…”

“…The increased stoichiometry with increased applied voltage is almost certainly due to the increased plasma energy allowing a higher degree of chemical reaction for a given substrate temperature, possibly via alternative pathways afforded by the formation of excited species. 37 The sub-stoichiometry was not perceived as a disadvantage for use as a hole blocking layer within a perovskite cell, given that in separate work 38 sub-stoichiometric sputtered titania had performed well in the intended cell constructions. It is suggested that the mobility of the oxygen vacancies and titanium interstitials may contribute to a reduction in series resistance regardless of the TiO 2Àx film being amorphous, polycrystalline or single crystal.…”

Atomic Layer Deposited Electron Transport Layers in Efficient Organometallic Halide Perovskite Devices

“…Other hole blocking layers include C60 [15], ZnO [16] and SnO2 [17][18][19][20]. The conformality of ALD allows for the deposition of very thin blocking layers over large areas when compared to conventional techniques [21][22][23].…”

Materials for Photovoltaics: State of Art and Recent Developments

“…For instance, the use of TiO 2 with fullerene as ETL enabled the fabrication of a hysteresis-free device, with an efficiency of 19.1% [ 101 ]. Additional layers should also be considered, such as the anti-reflective coating, as well as the thickness and strength of each layer [ 102 , 103 ].…”