Laser processing of TiO₂ films for dye solar cells: a thermal, sintering, throughput and embodied energy investigation

Abstract

We have analysed and optimised a laser process for the sintering of the TiO2 layers in dye solar cells (DSCs). Through a thermographic characterisation of the process, we show that it is possible to scale and process large areas uniformly (16 cm2). We fabricated DSCs with nanocrystalline (nc)‐TiO2 films sintered by using pulsed ultraviolet laser with an average output power P varying from 1 W to 7 W whilst mainting a constant power conversion efficiency η. The highest efficiency reached for a laser sintered DSC was 7%. The time required to sinter 1 m2 of nc‐TiO2 film was found to decrease hyperbolically with P, which is important for determining process takt times. We quantified the embodied energy (EE) required to sinter 1 m2 of the active TiO2 layer for a variety of different processes, and found that the EE for the laser sintering process with a system wall plug efficiency of 3.5% to be competitive with the more conventional oven and belt furnace treatments. We outline the main features required from a laser system to carry out an efficient, energetically favourable and industrially applicable automated process with competitive throughput. Copyright © 2012 John Wiley & Sons, Ltd.

Taking Temperature Processing Out of Dye‐Sensitized Solar Cell Fabrication: Fully Laser‐Manufactured Devices

“…[ 36 ] Finally, utilizing high wall plug effi ciency RSLSs, there is scope to set up a complete fabrication process with a low embedded energy, even favorable compared to conventional ones. [ 21 ] 4. Experimental Section nc-TiO 2 Film Laser Patterning : Two TCO/glass substrates (a) and (b) (4 cm × 4 cm each, Pilkington 8 Ω/ٗ) were coated with a nc-TiO 2 fi lm obtained after depositing via doctor blade (gap of 130 µm) a nc-TiO 2 based paste successively dried at 100 °C for 10 min over a hot plate.…”

“…In the process we developed, the two electrodes were pressed ( p = 1 atm) with the gasket placed inbetween, and irradiated with a CW diode laser system emitting in the near IR laser ( λ = 800 nm and λ = 960 nm) where the FTO/glass shows low absorption (absorptance < 20%). [ 21 ] The optimal laser power was found to be P = 50 W. Higher P values were observed to induce local burning and irregular material deformation, whereas lower values led to insuffi cient bonding. After laser sealing, to fi nish device fabrication, an electrolyte was injected in the sandwich structure.…”

“…Differently from the CO 2 laser, during the process no glass brakeage was observed, being the Nd:YVO 4 emission wavelength ( λ = 1064 nm) only weakly absorbed by the FTO/ Glass substrate (absorptance ≈25%). [ 21 ] …”

“…In order to avoid this, the laser wavelength was chosen in the visible range ( λ = 515 nm) where the transparent conductive oxide (TCO) coatedglass is highly transparent. [ 21 ] We then systematically investigated the effect of Φ on R s and on nc-TiO 2 ablation to extract the suitable window of operation. Laser patterning was operated before TiO 2 sintering.…”

“…[13][14][15][16][17][18] In particular, we have reported an effi cient, effective, scalable, and low embodied energy sintering procedure for the nc-TiO 2 fi lm. [19][20][21] Here we demonstrate that all the primary DSC manufacturing steps that required temperature treatments and in particular, sintering of the TiO 2 fi lm, curing of the Pt precursor, and device sealing, can be successfully and effi ciently carried out via laser assisted processes controlled by means of raster scanning systems (RSLSs). We believe this to be the fi rst demonstration of a device which is also effi cient and durable, where absolutely no temperature treatments were applied (all replaced by laser processing) together with a method for the defi nition of the cell pattern.…”