A piperidinium salt stabilizes efficient metal-halide perovskite solar cells by Lin, Y-H, Sakai, N, Da, P, Wu, J, Sansom, H, Ramadan, A, Mahesh, S, Liu, J, Oliver, R, Lim, J, Aspitarte, L, Sharma, K, Madhu, PK, Morales‐Vilches, A, Nayak, P, Bai, S, Gao, F, Grovenor, C, Johnston, M, Labram, J, Durrant, J, Ball, J, Wenger, B, Stannowski, B, Snaith, H