Highly efficient (>13%) and robust flexible perovskite solar cells using an ultra-simple all-carbon-electrode configuration

Fragile and expensive transparent conductive oxide anode and noble metal cathode 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 ultra-simple 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 exhibitslow sheet resistance, high light transmittance and superior flexibility beyond ITO. DFT calculations reveal that O atoms from GR anchored onto the interwoven CNTs network have strong covalent binding capacity with bond-deficient Sn ions, inhibiting the formation of oxygen vacancies in SnO₂. Such binding effect induces a significant reduction of the CB minimum of SnO₂, yielding favorable energy level alignment for carrier transport at the SnO₂/perovskite interface. Also, a heat-pressing approach as atiny trick is used to fill the gaps at the perovskite/carbon cathode interface. Theresulting 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 ultra-simple all-carbon-electrode offers a promising route for robust and cost-effective flexible photovoltaic devices.