Transparent conducting oxide top contacts for organic electronics

Abstract

A versatile method for the deposition of transparent conducting oxide (TCO) layers directly onto conjugated polymer thin film substrates is presented. Using pulsed laser deposition (PLD) we identify a narrow window of growth conditions that permit the deposition of highly transparent, low sheet resistance aluminiumdoped zinc oxide (AZO) without degradation of the polymer film. Deposition on conjugated polymers mandates the use of low growth temperatures (<200 C), here we deposit AZO onto poly-3hexylthiophene (P3HT) thin films at 150 C, and investigate the microstructural and electrical properties of the AZO as the oxygen pressure in the PLD chamber is varied (5-75 mTorr). The low oxygen pressure conditions previously optimized for AZO deposition on rigid substrates are shown to be unsuitable, resulting in catastrophic damage of the polymer films. By increasing the oxygen pressure, thus reducing the energy of the ablated species, we identify conditions that allow direct deposition of continuous, transparent AZO films without P3HT degradation. We find that uptake of oxygen into the AZO films reduces the intrinsic charge carriers and AZO films with a measured sheet resistance of approximately 500 U , À1 can be prepared. To significantly reduce this value we identify a novel process in which AZO is deposited over a range of oxygen pressuresenabling the deposition of highly transparent AZO with sheet resistances below 50 U , À1 directly onto P3HT. We propose these low resistivity films are widely applicable as transparent top-contacts in a range of optoelectronic devices and highlight this by demonstrating the operation of a semi-transparent photovoltaic device.

Transparent conductive ZnO layers on polymer substrates: Thin film deposition and application in organic solar cells

“…low efficiency (η = 0.5 %), in good agreement with results on very similar OSCs [45]. The lower efficiency of these OSCs might be due to the AZO deposition as oxygen ions and UV radiation in the PLD plasma may damage the exposed photoactive polymer.…”

Exploring and controlling intrinsic defect formation in SnO2 thin films

“…[1][2][3][4] Whilst the development of n-type TCOs have been thoroughly investigated e.g. indium tin oxide (ITO), aluminium doped zinc oxide (AZO), and indium doped zinc oxide (IZO) [5][6][7] the progress towards developing p-type analogues is significantly lacking, owing to the challenge of obtaining stable p-type characteristics. SnO 2 is an intrinsic n-type semiconductor with a wide direct band gap (3.6 eV), high optical transparency and compatibility with a range of deposition methods.…”

Probing the doping mechanisms and electrical properties of Al, Ga and In doped ZnO prepared by spray pyrolysis

“…[8][9][10][11][12] The conductivity of ZnO is considered to arise from a variety of native point defects including; oxygen vacancies (V O ), zinc interstitials (Zn i ), zinc anti-sites and more recently to the incorporation of interstitial hydrogen. 13 The charge carrier mobility and concentration in ZnO can be further enhanced by the inclusion of dopant atoms, typically group III elements 14,15 or by the creation of intrinsic defects via thermal treatments under vacuum, argon or hydrogen environments. 16 For the thermal treatments several mechanisms have been proposed, namely the creation of V O 17 which act as point defects contributing two electrons to the conduction band.…”