Layer conductance reduction and failure analysis due to bending for superflexible perovskite solar cells

Flexible perovskite solar cells (FPSCs) with excellent anti-bending ability are successfully fabricated, in which the novel cathode PEDOT:PSS:Li/ITO(20 nm) is used. With a bending radius of 1.0 cm, when the bending cycle, N, equals 0, 10 000 and 20 000, the power conversion efficiency as a function of N, η(N), is 13.91%, 10.86% and 3.45%, or 100%, 78% and 25% of η(0), respectively. During bending along an edge of our FPSC, we found that the reductions of layer conductance, φ(N), for the cathode, electron transport layer, perovskite layer, and hole transport layer are essential for reduction of η(N) due to bending. For each of the above constituent layer “i”, when N increases, the normalized layer conductance fi(N), i.e. φi(N)/φi(0), consistently and markedly decreases, and its reduction rate consistently increases. η(N) can be well fitted by the product of fi(N)mi for the mentioned four layers, and the power, mi, is determined by fitting. The “i” for the cathode is marked as “1”, and when the cathode is improved as mentioned, not only the reduction rate of f1(N) with N sharply decreases, but also the power, m1, largely decreases from 1.52 to 0.0076. When the novel cathode is used, the influence of its layer conductance reduction on η(N) reduction due to bending greatly decreases.