Surface Modification and Additive Engineering for Record High Efficiency Flexible Perovskite Solar Cells
Shengzhong Liu1,2
1Dalian National Laboratory for Clean Energy, iChEM, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, Dalian, China
/2Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119, Xi'an, China

An effective surface modification technique is developed to prepare SnO2 based electron transport layer. Together with an additive engineering strategy, solar cell efficiency is improved to over 22% for glass based rigid substrate. Using flexible PET substrate, flexible solar cells are designed and fabricated with the cell efficiency improved to as high as 20.9%, the highest efficiency for this category of flexible solar cells. It is found that by using an additive to react with Pb2+ to form an intermediate complex. Crystallization process is slowed down during the perovskite formation, leading to enlarged grain size and improved crystallin quality. In fact, using the SnO2 electron selective layer and the additive engineering, the trap state density of the resultant perovskite thin films is effectively reduced comparing to the films without it, demonstrating that the additive effectively retards transformation kinetics during the thin film formation process. Meanwhile, the surface modification is found critical to form a nucleation layer and a good interface for the perovskite thin film development. Meanwhile, the environmental stability of the Flexible solar cells is significantly enhanced comparing to the devices without them. Large area solar cells are fabricated to demonstrate its scalability.