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The greatest challenge for improving the power conversion efficiency of Cu2ZnSn(S,Se)4 (CZTSSe)/CdS/ZnO thin film solar cells is increasing the open circuit voltage (VOC). Probable leading causes of the VOC deficit in state-of-the-art CZTSSe devices have been identified as bulk recombination, band tails, and the intertwined effects of CZTSSe/CdS band offset, interface defects, and interface recombination. In this work, we demonstrate the modification of the CZTSSe absorber/CdS buffer interface following the deposition of 1 nm-thick Al2O3 layers by atomic layer deposition (ALD) near room temperature. Capacitance-voltage profiling and quantum efficiency measurements reveal that ALD-Al2O3 interface modification reduces the density of acceptor-like states at the heterojunction resulting in reduced interface recombination and wider depletion width. Indications of increased VOC resulting from the modification of the heterojunction interface as a result of ALD-Al2O3 treatment are presented. These results, while not conclusive for application to state-of-the-art high efficiency CZTSSe devices, suggest the need for further studies as it is probable that interface recombination contributes to reduced VOC even in such devices.

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Ă ĞƉĂƌƚŵĞŶƚ ŽĨ ůĞĐƚƌŝĐĂů ĂŶĚ ŽŵƉƵƚĞƌ ŶŐŝŶĞĞƌŝŶŐ͕ hŶŝ|ĞƌƐŝƚLJ ŽĨ hƚĂŚ͕ ^Ăůƚ >ĂŬĞ ŝƚLJ͕ hd͕ ϴϰϭϭϮ͕ h^ ď Yd ^ŽůĂƌ /ŶĐ͕͘ ^ƵŶŶLJ|ĂůĞ͕ ͕ ϵϰϬϴϲ͕ h^ Đ EĂƚŝŽŶĂů ZĞŶĞǁĂďůĞ ŶĞƌŐLJ >ĂďŽƌĂƚŽƌLJ͕ ϭϲϭϳ ŽůĞ ů|Ě͕͘ 'ŽůĚĞŶ͕ K͕ ϴϬϰϬϭ͕ h^ Ě ĞƉĂƌƚŵĞŶƚ ŽĨ DĂƚĞƌŝĂůƐ ^ĐŝĞŶĐĞ ĂŶĚ ŶŐŝŶĞĞƌŝŶŐ͕ hŶŝ|ĞƌƐŝƚLJ ŽĨ hƚĂŚ͕ ^Ăůƚ >ĂŬĞ ŝƚLJ͕ hd͕ ϴϰϭϭϮ͕ h^ ^dZ d ĞƐƉŝƚĞ ƚŚĞ ŵĂŶLJ ƐŝŵŝůĂƌŝƚŝĞƐ ďĞƚǁĞĞŶ Ƶ Ϯ Ŷ^Ŷ;^͕^ĞͿ ϰ ; d^^ĞͿ ĂŶĚ Ƶ;/Ŷ͕'ĂͿ;^͕^ĞͿ Ϯ ŵĂƚĞƌŝĂůƐ ĂŶĚ ĚĞ|ŝĐĞ ĂƌĐŚŝƚĞĐƚƵƌĞ͕ ŽƉĞŶ ƋƵĞƐƚŝŽŶƐ ƌĞŵĂŝŶ ĂďŽƵƚ ƚŚĞ ŽƉƚŝŵĂů ƐƵƌĨĂĐĞ ƉƌĞƉĂƌĂƚŝŽŶ ƐƚĞƉƐ ĨŽƌ d^^Ğ ĂďƐŽƌďĞƌƐ͕ ŝŶĐůƵĚŝŶŐ ǁŚĞƚŚĞƌ ĚŝĨĨĞƌĞŶĐĞƐ ĞdžŝƐƚ ĨŽƌ ĂďƐŽƌďĞƌ ůĂLJĞƌƐ ĚĞƉŽƐŝƚĞĚ ďLJ ĚŝĨĨĞƌĞŶƚ ŵĞƚŚŽĚƐ͘ /Ŷ ƚŚŝƐ ǁŽƌŬ͕ ǁĞ ŝŶ|ĞƐƚŝŐĂƚĞ < E ĞƚĐŚŝŶŐ ĂŶĚ E, ϰ K, ƚƌĞĂƚŵĞŶƚ ĂƐ ƐƵƌĨĂĐĞ ƉƌĞƉĂƌĂƚŝŽŶ ŵĞƚŚŽĚƐ ĨŽƌ ƚŚĞ ĂďƐŽƌďĞƌͬ Ě^ ŝŶƚĞƌĨĂĐĞ ĨŽƌ ƚǁŽͲƐƚĂŐĞ ƉƌŽĐĞƐƐĞĚ d^^Ğ ĂŶĚ ĐŽͲĞ|ĂƉŽƌĂƚĞĚ d^Ğ ĂďƐŽƌďĞƌ ůĂLJĞƌƐ͘ ŵďŝĞŶƚͲĞdžƉŽƐĞĚ͕ ƚŚƵƐ ŽdžŝĚŝnjĞĚ ĂŶĚ ĐŽŶƚĂŵŝŶĂƚĞĚ͕ ƚŚŝŶ Ĩŝůŵ ĂďƐŽƌďĞƌƐ ĂƌĞ ƵƚŝůŝnjĞĚ ƚŽ ĞdžĂŵŝŶĞ ƚŚĞ ĞĨĨĞĐƚŝ|ĞŶĞƐƐ ŽĨ ƚŚĞƐĞ ƐƵƌĨĂĐĞ ƉƌĞƉĂƌĂƚŝŽŶ ŵĞƚŚŽĚƐ ĂŶĚ ƚŽ ĞůƵĐŝĚĂƚĞ ƚŚĞŝƌ ĞĨĨĞĐƚƐ ŽŶ ĚĞ|ŝĐĞ ƉĞƌĨŽƌŵĂŶĐĞ͘ dŽƉŽŐƌĂƉŚLJ ĂŶĚ ƐƵƌĨĂĐĞ ƉŽƚĞŶƚŝĂů ŝŵĂŐĞƐ ƐŝŵƵůƚĂŶĞŽƵƐůLJ ŽďƚĂŝŶĞĚ ďLJ <Ğů|ŝŶ ƉƌŽďĞ ĨŽƌĐĞ ŵŝĐƌŽƐĐŽƉLJ ;

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