  Indoor photovoltaics are receiving tremendous attention due to the continuous
development of the Internet of Things (IoT). Here we report a triple anion (TA)
perovskite CH3NH3PbI2.6(BrCl)0.2 with a tailored bandgap suitable for
maximizing indoor light harvesting compared to methyl ammonium lead iodide
CH3NH3PbI3. The best-performing TA perovskite indoor-photovoltaic device
achieved a steady-state power conversion efficiency (PCE) of 25.1% with an
output power density of ~ 75 microW/cm2 under 1000 lux indoor illumination
  (0.3 mW/cm2 irradiance). This PCE is almost 40% higher than that of
equivalent CH3NH3PbI3-based devices (PCE of 17.9%). Longer carrier lifetime,
reduced density of trap states and improved crystalline quality were achieved
by the triple anion alloying method. The decisive role of chlorine (Cl) in the
better performance of TA-based indoor photovoltaic devices was further
investigated by successively reducing the Cl content and correlating it with
the corresponding photovoltaic device performance. Replacing the commonly used
hole transporting layer of Spiro-MeOTAD with undoped P3HT was found to
significantly reduce the current-voltage hysteresis under indoor lighting
conditions. A graphene-coated textile fiber-based temperature sensor was
successfully powered by the triple anion perovskite indoor photovoltaic
devices. The results from the present study demonstrate a novel route to
maximize the PCE of halide perovskite indoor photovoltaic devices and their
potential for application in the IoT industry.
