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Contrasting Effects of Organic Chloride Additives on Performance of Direct and Inverted Perovskite Solar Cells

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journal contribution
posted on 01.10.2019 by Pang Wang, Hui Wang, Fanghao Ye, Huijun Zhang, Mengting Chen, Jinlong Cai, Donghui Li, Dan Liu, Tao Wang
Perovskite solar cells (PSCs) have demonstrated encouraging progress in recent years. Additive engineering, where diverse additives are incorporated into the perovskite layer, has been widely adopted to tune the perovskite grains, reduce defect density and charge recombination. Here, we observe a universal phenomenon that organic chloride additives enhance the open circuit voltage (VOC) and power conversion efficiencies (PCEs) of direct PSCs but decrease the VOC, short-circuit current (JSC), and PCE of inverted PSCs, regardless of the choice of charge transport materials. The polyTPD-based direct device incorporating trimethylammonium chloride (TACl) additive delivery improved PCE from 17.8 to 20.0%, arising from the enhanced VOC from 1.03 to 1.12 V. With the same content of TACl, the best PCE of the polyTPD-based inverted device decreased from 20.2 to 18.5% because of the reduced VOC (1.05–1.01 V) and JSC (23.2–22.5 mA/cm2). Our investigation confirms that organic chloride will p-dope perovskites and elevate the work functions, which lead to favorable/unfavorable charge transfer between perovskite films and its upper transport layers in direct and inverted devices. This work provides an insight into the rational design of the device structure when applying additives which can dope the perovskite to affect charge transfer at the perovskite/charge transport layer interface.