Optical simulations to inform the design of UV-absorbing organic materials and solar cells

Abstract

Organic solar cells are ideal for semi-transparent applications given their “peaky” absorption, which allows them to selectively absorb photons outside the visible range while transmitting visible light. Such devices embody a fundamental tradeoff between transparency and power generation that must be optimized to fit the requirements of each potential application—for example, powering electrically dimmable smart windows. To inform the design of organic ultraviolet-absorbers and solar cells that target such applications, we computer-generate sets of optical constants with a range of absorption coefficients and absorption cutoff wavelengths that mimic those of real organic semiconductors. We then perform optical transfer-matrix simulations to determine the absorption and transmission spectra of full-stack photovoltaic cells, inserting these computer-generated optical constants to describe the photoactive absorbing layers. We find that solar cells having absorbers with a cutoff wavelength of 420 nm produce the most power without degrading transparency or color neutrality, and that absorption coefficients up to 5 × 105 cm−1 are needed to fully absorb the targeted wavelengths within practical photoactive layer thicknesses <300 nm in the absence of a reflecting electrode.