SPLTRAK Abstract Submission
The Effect of Residual PbI2 on 2-Step Vapor-Processed p-i-n and n-i-p MAPbI3 Solar Cells
Austin G Kuba, Alexander J Harding, Chaiwarut Santiwipharat, Ujjwal K Das, Kevin D Dobson, William N Shafarman
Institute of Energy Conversion, University of Delaware, Newark, DE, United States

Solar cells were made with MAPbI3 deposited by a two-step close space vapor transport (CSVT) deposition process and identical materials and deposition techniques in n-i-p and p-i-n architectures. Evaporated C60 ETL and copper phthalocyanine (CuPC) HTLs were used as contact layers. P-i-n solar cell J-V curves are well-behaved while n-i-p solar cells initially have s-shaped J-V curves that become well-behaved upon light soaking, possibly due to the substrate work function or integer charge transfer effects from the substrates. The CSVT reaction proceeds by conversion of a PbI2 layer via reaction with methylammonium iodide (MAI), where the diffracted intensity of the residual PbI2 reflects the degree of conversion of the film. N-i-p solar cells lose performance when there is no residual PbI2 in the film, which may be explained by excess mobile ions diffusing through the film into the C60 layer and reducing the carrier concentration. This is tested by treatment of C60 with KI/IPA solution, which produces a stronger s-shaped J-V curve. In contrast, p-i-n solar cells perform well without residual PbI2 due to the improved chemical stability of the CuPC HTL with the perovskite and excess MAI. This study highlights the flexibility of the 2-step close space vapor process for producing multiple solar cell architectures and the need to choose contact layers that are not degraded by the perovskite and excess MAI in 2-step vapor processes.