Improvement to thin film CdTe solar cells with controlled back surface oxidation

Abstract

Debbie (2015) Improvement to thin film CdTe solar cells with controlled back surface oxidation. Solar Energy Materials and Solar Cells, 136. pp. 213-217.

Progression of metalorganic chemical vapour‐deposited CdTe thin‐film PV devices towards modules

“…The difficulty with p-type doping of CdTe is a well-known phenomenon that is often attributed to acceptor compensation [17][18][19]. The rise in the net acceptor density reported in this work for the air-annealed cells in Figure 1 may be inferred to be a result of the incorporation of oxygen into the CdTe structure: air annealing has previously been determined to introduce oxygen into CdTe films for both MOCVD material [11] (by X-ray photoemission spectroscopy) and CSS material [20] (by secondary-ion mass spectroscopy). This rise in the net carrier density correlates with the V oc boost observed with the air anneal.…”

“…V oc and FF: impact of air annealing. The carrier density for representative solar cells, with (T ann = 80 min) and without air annealing, was determined by C-V measurements ( Figure 1) to explore if the carrier density is likely to contribute to the V oc and FF enhancement observed [11]. A U-shaped carrier concentration profile, typical of thin-film CdTe-based devices, is observable for all samples.…”

“…Because air-anneal treatment caused small losses in J sc [11], thinning of the window layer was evaluated as a way to enhance the photocurrent to maximise the PV performance. The results of these experiments are demonstrated in Table I and Figure 2 where a significant increase in J sc was obtained by reducing the window layer from 240 (baseline [9][10][11][12]) to 100 nm. For 150-nm window devices, the performance is improved, whilst the uniformity is comparable with 240-nm window thickness.…”

“…However, for the MOCVD devices grown at the Centre for Solar Energy Research, in addition to CdCl 2 treatment, the devices are also doped with As during growth, and this is necessary to achieve high performance [10]. However, it has been shown in a recent study [11] that a post-deposition low-temperature annealing in air (prior to back contact metallization) acts to improve the overall device performance: enhancements in both V oc and FF were observed for anneals up to 180 min, despite a decline in J sc also began after 60 min. Whilst it was demonstrated by Rugen-Hankey et al [11] that the annealing introduced oxygen into the CdTe layers, the mechanism of the device improvement was not investigated further.…”

Optimization of physical properties of vacuum evaporated CdTe thin films with the application of thermal treatment for solar cells

“…It has enormous potential applications in the field of optoelectronic devices like solar cells, optical and nuclear detectors, light-emitting diodes (LEDs), field effect transistors, nonlinear integrated optical devices, lasers etc. The theoretical conversion efficiency of polycrystalline CdTe thin film solar cells is high (29%) and maximum reported experimental conversion efficiency is 20.4% [10][11][12][13][14][15].…”