Charge-Transfer States at the Fullerene Interface Cause Nonradiative Recombination Losses in Sn-Based Perovskite Solar Cells

Tin-based perovskite solar cells (PSCs) are emerging as a more environmentally friendly alternative to traditional PSCs that typically contain toxic lead. In this work, we study the influence of the Sn-perovskite/fullerene interface on the open-circuit voltage (Voc). When the fullerene derivative ICBA is used as the electron transport layer, the Voc reaches 0.68 V, while the band gap of the Sn-perovskite is 1.44 eV, giving a voltage deficit of 0.76 V. Using PCBM as the electron transport layer, this deficit is 0.19 V higher. Herein, we identify through Fourier transform photocurrent spectroscopy and luminescence measurements that interfacial charge-transfer states at the Sn-perovskite/fullerene interface induce a nonradiative recombination channel. The energy of these states should be increased in order to mitigate voltage losses at the contacts