To further increase the open-circuit voltage (V oc) of perovskite solar cells (PSCs), many efforts have been devoted to doping the TiO2 electron transport/selective layers by using metal dopants with higher electronegativity than Ti. However, those dopants can introduce undesired charge traps that hinder charge transport through TiO2, so the improvement in the V oc is often accompanied by an undesired photocurrent density–voltage (J–V) hysteresis problem. Herein, it is demonstrated that the use of a rapid flame doping process (40 s) to introduce cobalt dopant into TiO2 not only solves the J–V hysteresis problem but also increases the V oc and power conversion efficiency of both mesoscopic and planar PSCs. The reasons for the simultaneous improvements are two fold. First, the flame-doped Co-TiO2 film forms Co-Ov (cobalt dopant-oxygen vacancy) pairs and hence reduces the number density of Ti3+ trap states. Second, Co doping upshifts the band structure of TiO2, facilitating efficient charge extraction. As a result, for planar PSCs, the flame doping of Co increases the efficiency from 17.1% to 18.0% while reducing the hysteresis from 16.0% to 1.7%. Similarly, for mesoscopic PSCs, the flame doping of Co increases the efficiency from 18.5% to 20.0% while reducing the hysteresis from 7.0% to 0.1%.
Bibliographical noteFunding Information:
J.K.K. and S.U.C. contributed equally to this work. The authors acknowledge the support of the Yonsei University Future-leading Research Initiative of 2015 (2015-22-0067) and the NRF of Korea Grant funded by the Ministry of Science, ICT, and Future Planning (2016R1A2A1A05005216 and 2018R1D1A1B07050875). X.L.Z. acknowledges the support of the Stanford Precourt Institute for Energy. Y.J. acknowledges the support of Knut and Alice Wallenberg Foundation. J.H.P. acknowledges the support of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No.20163010012450 and 20173010013340).
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All Science Journal Classification (ASJC) codes
- Renewable Energy, Sustainability and the Environment
- Materials Science(all)