Interfacial barrier height modification of indium tin oxide/a-Si:H(p) via control of density of interstitial oxygen for silicon heterojunction solar cell application

• Published in: Thin solid films 2013-11, Vol.546, p.342-346
• Main Authors: Ahn, Shihyun, Kim, Sunbo, Dao, Vinh Ai, Lee, Seungho, Iftiquar, S.M., Kim, Doyoung, Hussain, Shahzada Qamar, Park, Hyeongsik, Lee, Jaehyeong, Lee, Youngseok, Cho, Jaehyun, Kim, Sangho, Yi, Junsin
• Format: Article
• Language: English
• Subjects: Applied sciences; Barriers; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Density; Electrodes; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Energy; Exact sciences and technology; Free-carrier absorption; Heterojunction solar cells; Heterojunctions; Indium tin oxide; Interstitial oxygen density; Interstitials; Natural energy; Photovoltaic conversion; Physics; Silicon; Solar cells. Photoelectrochemical cells; Solar energy; Structure and morphology; thickness; Surface double layers, schottky barriers, and work functions; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Work function
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2013.05.132

An indium tin oxide (ITO) film with low carrier concentration (n), high mobility (μ) and high work function (ΦITO) is a beneficial material for the front electrode in heterojunction silicon (HJ) solar cells due to its low free-carrier absorption in the near-infrared wavelength and low Schottky barrier height at the ITO/emitter-layer front contact. This low free-carrier absorption as well as the low Schottky barrier height increase the open-circuit voltage (Voc) and the short-circuit current density (Jsc), which in turn increases the overall cell efficiency (η). Hence, ITO films with lower n, higher μ and higher ΦITO were prepared by controlling the density of the interstitial oxygen [Oi] in the films and used as anti-reflection electrodes in HJ solar cells. With increasing [Oi] in the ITO, the preferential orientation of the (222) crystalline plane became more dominant. The ΦITO and μ increased from 4.87eV and 38.9 cm2V−1s−1 to 5.04eV and 48.79 cm2V−1s−1, respectively, whereas n decreased from 4.7×1020cm−3 to 2.8×1020cm−3. We attribute these changes to the chemisorbed oxygen into the ITO films, while the decrease of n is due to the ability of interstitial oxygen to capture electron, and the increase of μ is due to the reduction in free-carrier scattering. These ITO films were used to fabricate HJ solar cells. As [Oi] in the ITO film increased, the device performance improved and the best cell performance was obtained with Voc of 714mV, Jsc 34.79mA/cm2 and η of 17.82%. By computer simulation, we found that the higher ΦITO and μ but lower n were responsible for the enhanced cell performance. The cell performance, however, deteriorated due to poor film properties when [Oi] exceeded concentration limit from 3.2×1020cm−3. •The carrier concentration (n) decreases with increasing interstitial oxygen ([Oi]).•The Hall mobility (μ) and the work function (ΦITO) increases with increasing ([Oi].•High μ and high ΦITO but low n is beneficial for cell performance.•The best cell performance was obtained as [Oi] of 3.2×1020cm−3.