Highly Efficient (>13%) and Robust Flexible Perovskite Solar Cells Using an Ultrasimple All-Carbon-Electrode Configuration

Fragile and expensive transparent conductive oxide anodes and noble metal cathodes in typical perovskite photovoltaic devices pose unavoidable issues, i.e., poor flexibility and high material cost, making it inaccessible to commercial application. Here, we report an ultrasimple indium tin oxide (ITO)-free and HTL-free all-carbon-electrode flexible perovskite solar cell (AC-F-PSC) with an architecture of PEN/carbon/SnO2/perovskite/carbon which contains an anode made of a carbon-based integrator (CNT-GR) comprising carbon nanotubes and low-dose graphene, and a cathode made of the commonly used conductive carbon. The CNT-GR anode exhibits low sheet resistance, high light transmittance, and superior flexibility beyond ITO. Density functional theory calculations reveal that O atoms from GR anchored onto the interwoven CNT network have strong covalent binding capacity with bond-deficient Sn ions, inhibiting the formation of oxygen vacancies in SnO2. Such a binding effect induces a significant reduction of the conduction band minimum of SnO2, yielding favorable energy level alignment for carrier transport at the SnO2/perovskite interface. Also, a heat-pressing approach as a tiny trick is used to fill the gaps at the perovskite/carbon cathode interface. The resulting AC-F-PSC device attains an efficiency of 13.14%, which is a record value among reported carbon-electrode F-PSCs, with superior mechanical flexibility, i.e., ∼71% of initial efficiency after bending 4000 cycles at 4 mm bending radius. This PSC based on an ultrasimple all-carbon-electrode offers a promising route for robust and cost-effective flexible photovoltaic devices.