ITO Top‐Electrodes via Industrial‐Scale PLD for Efficient Buffer‐Layer‐Free Semitransparent Perovskite Solar Cells

Abstract

well-established state-of-the-art devices such as silicon heterojunction solar cells and inorganic and organic light-emitting diodes (LEDs) to perovskite solar cells (PSCs), and organic solar cells. [5][6][7][8] There are also many examples of TCOs in new approaches that simultaneously require semitransparency and flexibility, such as semitransparent conductors, field-effect transistors, thermal shields, photo-detectors, and vertical transistors. [9][10][11][12][13][14] PSCs have attracted much interest since their onset in 2009 due to rapidly-increasing power conversion efficiencies (currently above 25% for small area cells). The perovskite layer and any adjacent charge transport layers can be fabricated in many ways using either solution-based processes or vacuum-assisted deposition. Vacuum-based deposition has the advantage of better control over the film thickness and is an additive method, moreover, it is a widely employed method of production of the before mentioned opto-electronic devices. [15,16] Despite the benefits and promising perspectives of using TCOs in optoelectronics, the development of organic/TCO (TCO on top of organic) bi-layer structures is still a non-trivial challenge because of the generally harsh processing conditions involved in the deposition of the TCO layers. [17] For both lab-and industrial-scale deposition of TCO, magnetron sputtering is the most widespread technique. It is a vacuumbased process that employs direct current or radio frequency to excite a carrier gas (most commonly Ar) into a high kinetic energy plasma which bombards a target material, resulting in the transfer of fragments from the target to substrates positioned above it. However, the accelerated particles, together with side phenomena such as plasma luminescence and processing-induced heat, can easily damage soft organic semiconductor layers, leading to increased leakage current, as well as reduced efficiency and a lower lifetime of the optoelectronic device. [18,19] To overcome this limitation, a protective buffer layer is deposited prior to the TCO deposition. [17] Also, many efforts were proposed to minimize damages of sputtering deposition on buffer-layer-free stacks by lowering the power density threshold by changes in power, target to substrate distance, sputtering gas, and process pressure, [20][21][22][23][24] but at the expense of longer processing times. [22,[25][26][27][28][29] Among these reports, the most efficient buffer-layer-free PSC using TCO top-electrode was achieved by Ramos et al. employing a post-annealed ITO sputtered directly onto a thick (290 nm) spiro-OMeTAD hole The deposition of transparent conductive oxides (TCO) usually employs harsh conditions that are frequently harmful to soft/organic underlayers. Herein, successful use of an industrial pulsed laser deposition (PLD) tool to directly deposit indium tin oxide (ITO) films on semitransparent vacuum-deposited perovskite solar cells without damage to the device stack is demonstrated. The morphological, electronic, and optical properties o...

Semitransparent near-infrared Sn–Pb hybrid perovskite photodetectors

“…This approach decreased the series resistance of devices finished with PLD-ITO from 17.4 to 4.8 mO cm À2 , within the same order of magnitude as devices using the metal top contact (B3.5 mO cm À2 ). 50 The transmittance of the full stack using 200 nm perovskite films was measured (Fig. 1d).…”

“…For example, in our recent investigation, bifacial MAPbI 3 perovskite solar cells were fabricated by directly depositing ITO with PLD on top of the organic C 60 /BCP electron transport layers (ETLs) with a total thickness of only 32 nm, without any protective buffer layers in between, leading to no damage to the device stack underneath and, hence, no losses in photovoltaic performance. 50 Therefore, for the fabrication of the semitransparent MA 0.3 FA 0.7 Pb 0.5 Sn 0.5 I 3 photodetectors investigated here, the ITO top cathode was also deposited via PLD directly on top of the C 60 /BCP ETLs, using the optimized conditions previously obtained. 50 In order to prove that the deposition of the ITO top electrode was not harmful to the organic stack underneath, reference devices with a standard opaque Cu top contact (100 nm), instead of ITO, were also prepared by thermal vacuum deposition, for comparison.…”

“…50 Therefore, for the fabrication of the semitransparent MA 0.3 FA 0.7 Pb 0.5 Sn 0.5 I 3 photodetectors investigated here, the ITO top cathode was also deposited via PLD directly on top of the C 60 /BCP ETLs, using the optimized conditions previously obtained. 50 In order to prove that the deposition of the ITO top electrode was not harmful to the organic stack underneath, reference devices with a standard opaque Cu top contact (100 nm), instead of ITO, were also prepared by thermal vacuum deposition, for comparison. Although the resistivity of the PLD-ITO films is quite low (between 0.4 to 1 mΩ cm, depending on the deposition pressure, for thicknesses of ca.…”

“…This approach decreased the series resistance of devices finished with PLD-ITO from 17.4 to 4.8 mΩ cm −2 , within the same order of magnitude as devices using the metal top contact (∼3.5 mΩ cm −2 ). 50…”

“…The source material for ITO deposition was a Sn:In 2 O 3 ceramic target with 2 : 98 wt% and the chamber pressure was set at 0.033 mbar, with an O 2 partial pressure of 0.007 mbar controlled by a constant injection of an oxygen/argon gas mix, as optimized in our previous paper. 50 Shadow masks were used during the ITO deposition to obtain a final active area of 0.06 cm 2 . The Au grids (100 nm thick) at the side of the PLT-ITO cathodes were thermally evaporated.…”