12% efficient CdTe/CdS thin film solar cells deposited by low-temperature close space sublimation

Abstract

We report 12% efficient CdS/CdTe thin film solar cells prepared by low temperature close space sublimation (CSS). Both semiconductor films, CdS and CdTe, were deposited by high vacuum CSS in superstrate configuration on glass substrates with fluorine doped tin oxide (FTO) front contact. The CdTe deposition was carried out at a substrate temperature (Tsub) of 340° C, which is much lower than that used in conventional processes (>500 ° C). The CdTe films were treated with the usual CdCl 2 activation process. Different optimal annealing times and temperatures were found for low-temperature cells (Tsub 340°C) compared to high-temperature cells (Tsub = 520°C). The influence of the activation step on the morphology of high-temperature and low-temperature CdTe is determined by XRD, AFM, SEM top views, and SEM cross-sections. Grain growth, strong recrystallization, and a reduction of planar defects during the activation step are observed, especially for low-temperature CdTe. Further, the influence of CdS deposition parameters on the solar cell performance is investigated by using three different sets of parameters with different deposition rates and substrate temperatures for the CdS preparation. Efficiencies about 10.9% with a copper-free back contact and 12.0% with a copper-containing back contact were achieved using the low temperature CdTe process

Review of the CdCl2 Treatment Used in CdS/CdTe Thin Film Solar Cell Development and New Evidence towards Improved Understanding

“…Numerous reports [21][22][23][24][25][26] conclude that the XRD peaks observed show recrystallisation and grain growth after CdCl 2 treatment. Heat treatment alone, without CdCl 2 , also shows this trend, but the presence of CdCl 2 enhances the recrystallisation.…”

“…However, some research groups have reported that as-grown CdTe layers have (111) preferred orientation but after CdCl 2 treatment, the intensity of the (111) peak reduces and the other two peaks (220) and (311) become visible and the material therefore loses the preferential orientation along the (111) plane and becomes poly-crystalline [20][21][22][23][24][25][26][27]. There are also reports concluding that there is no grain growth if the starting CdTe layer has large grains [9].…”

Study the efficiency of single crystal CdTe/ZnCdS solar cell at various temperatures and illumination levels

“…Hadrich et al (2007) produced CdS/CdTe based solar cell which shows efficiency s = 8.2% with V oc = 0.68 V, J sc = 21.3 mA cm −2 , and ff = 0.57. Seymour (2005) produced CdTe based solar cells treated with Cu, having an efficiency s = 12.4% with V oc = 0.82 V, J sc = 23.9 mA cm −2 and ff = 0.63 and Jvdith (Schaffner et al, 2011) shows efficiency 12% by using copper in CdTe. Razkov also shows the latest evaluation of the conversion efficiencies of various type of research PV Cells (Razkov et al, 2011).…”

Growth of AgGaTe2 Layers by a Closed-Space Sublimation Method

“…[1][2][3][4][5][6][7] Also, chalcopyrite I-III-VI 2 compounds have recently attracted attention as potential components for semiconductor devices, including applications in solar cells and electrooptic devices. [8][9][10] In particular, CuInSe 2 has already become widely used in making commercial solar cells.…”