Band‐Offset Engineering for Enhanced Open‐Circuit Voltage in Polymer–Oxide Hybrid Solar Cells

Abstract

Abstract The power conversion efficiency of organic and hybrid solar cells is commonly reduced by a low open‐circuit voltage ( V OC ). In these cases, the V OC is significantly less than the energy of the lowest energy absorbed photon, divided by the elementary charge q . The low photovoltage originates from characteristically large band offsets between the electron donor and acceptor species. Here a simple method is reported to systematically tune the band offset in a π‐conjugated polymer–metal oxide hybrid donor–acceptor system in order to maximize the V OC . It is demonstrated that substitution of magnesium into a zinc oxide acceptor (ZnMgO) reduces the band offset and results in a substantial increase in the V OC of poly(3‐hexylthiophene) (P3HT)–ZnMgO planar devices. The V OC is seen to increase from 500 mV at x = 0 up to values in excess of 900 mV for x = 0.35. A concomitant increase in overall device efficiency is seen as x is increased from 0 to 0.25, with a maximum power‐conversion efficiency of 0.5 % obtained at x = 0.25, beyond which the efficiency decreases because of increased series resistance in the device. This work provides a new tool for understanding the role of the donor–acceptor band offset in hybrid photovoltaics and for maximizing the photovoltage and power‐conversion efficiency in such devices.