Abstract
Understanding the exciton dissociation process in organic solar cells is a fundamental issue for the design of high-performance photovoltaic devices. In this article, a parameterized quantum theory based on a coarse-grained tight-binding model plus non-local electron-hole interactions is presented, while the diffusion and recombination of excitons are studied in a square lattice of excitonic states, where a real-space renormalization method on effective chains has been used. The Hamiltonian parameters are determined by fitting the measured quantum efficiency spectra and the theoretical short-circuit currents without adjustable parameters show a good agreement with the experimental ones obtained from several polymer:fullerene and polymer:polymer heterojunctions. Moreover, the present study reveals the degree of polymerization and the true driving force at donor-acceptor interface in each analyzed organic photovoltaic device.
Highlights
Harvesting solar energy through photovoltaic devices constitutes one of the most active ways to solve the rapid growth of global electricity requirements, given that in one hour the earth receives enough energy from the sun to satisfy current human needs for a year [1]
The efficiency of an organic photovoltaic device is sensitively dependent on the active layer morphology, whose structure can be divided into three sections in a polymer:fullerene bulk heterojunction: (1) a pure polymer region, (2) a pure fullerene region, and (3) donor:acceptor interface one [15]
The internal quantum efficiency (IQE) of organic photovoltaic devices can be calculated in terms of the electron-hole recombination rate (Γ) and the effective self-energy at the impurity site U, Σ0 ( E), when both the electron and the hole are found at the photocell or donor molecule
Summary
Harvesting solar energy through photovoltaic devices constitutes one of the most active ways to solve the rapid growth of global electricity requirements, given that in one hour the earth receives enough energy from the sun to satisfy current human needs for a year [1]. The efficiency of an organic photovoltaic device is sensitively dependent on the active layer morphology, whose structure can be divided into three sections in a polymer:fullerene bulk heterojunction: (1) a pure polymer region, (2) a pure fullerene region, and (3) donor:acceptor interface one [15]. The latter has a crucial role in the light absorption, electron-hole recombination, and exciton dissociation, and determines the PCE. The calculated IQE and JSC are compared with those measured in several polymer: fullerene and polymer: non-fullerene photovoltaic devices
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