1-Consider an organic solar cell consisting of a TiO2 semiconductor with an ionization energy 7.8eV and a polymer with an electron affinity 3.4eV. Which of the followning band diagrams corresponds to the organic solar cell. The band gap of TiO2 is 3.5eV.

(a) (b)
2-What is the driving force in eV for electron injection from the polymer to the semiconductor



3-The electron diffusion coefficient is De=4∗10−5cm2/s and the thickness of TiO2 is 4μm. What is the lifetime of the injected electronsin ms?

Q.1 (a)

Q.2 answer = 0.9
Q.3 answer = 4

Q.1 (a)

Q.2 answer = 0.9
Q.3 answer = 4

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To answer these questions, we need to understand a few concepts related to band diagrams, electron injection, and lifetime of injected electrons. Let's break down each question and explain how to get the answer.

1. To determine which band diagram corresponds to the organic solar cell, we need to consider the ionization energy and electron affinity of the semiconductor and polymer. The band gap of TiO2 is also given.

The ionization energy represents the energy required to remove an electron from an atom or molecule, while the electron affinity represents the energy change when an electron is added to an atom or molecule. In a solar cell, electrons are injected from the polymer (donor) to the semiconductor (acceptor). For efficient electron injection, there should be an energy level alignment between the donor and acceptor.

To find the correct band diagram, we need to compare the energy levels of the donor and acceptor with the energy levels of the TiO2 conduction band and valence band. The band gap of TiO2 is known to be 3.5eV. We should look for a diagram where the energy levels of the polymer align with the conduction band of TiO2 and the energy levels of the TiO2 semiconductor align with the valence band of the polymer.

By comparing the energy levels, we can determine the correct band diagram.

2. The driving force for electron injection from the polymer to the semiconductor is the difference in energy between the highest occupied molecular orbital () of the polymer and the conduction band edge of the semiconductor. This energy difference can be calculated by subtracting the electron affinity of the polymer from the ionization energy of the semiconductor.

3. The lifetime of the injected electrons can be calculated using the following equation:

Lifetime = (thickness^2) / (2 * diffusion coefficient)

where the thickness is given as 4 μm and the electron diffusion coefficient (De) is given as 4 * 10^-5 cm^2/s. By substituting these values into the equation, we can calculate the lifetime of the injected electrons in milliseconds.

By understanding these concepts and using the provided data, we can find the answers to the questions.

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