Theory of high photovoltages in semiconducting films

Abstract

A theory of photo‐e.m.f. much exceeding the energy gap is given for various semiconducting films based on the assumption of periodicity of the film parameters. The equations describing space charge, transport, and generation‐recombination of current carriers are solved rigorously under periodic boundary conditions. The layer can be treated as an array of photocells, forming effectively an integrated circuit. Expressions for photovoltage are given and discussed in the limits of low and high illumination. Some integral inequalities being the conditions for the solutions to have a physical meaning are discussed. It is found that a phase shift between space charge and generation‐recombination distributions as functions of x is essential for the occurrence of high photovoltage. The space charge may be due either to charged donor and acceptor centres and occur already in dark or may be due to light induced trapped charge. Rise and decay of photovoltage are discussed and the possibility of obtaining fast effects is indicated.

Quasi Fermi Level Scan of Band Gap Energy in Photojunction

“…2) Dividing formula (2.2) by (2.1) we can correlate the change of minority electron concentration from n 20 to n 21 with the change of the quasi Fermi level F 2n [7]:…”

“…Continuously ongoing advanced studies aimed at indepth understanding of the physics of photovoltaic heterojunctions [1][2][3][4][5][6][7][8][9] and improvement of construction of solar cells [10][11][12][13][14][15] and ultraviolet sensitive photodetectors [16][17][18] are in line with the search of renewable energy sources supporting the sustainable civilization development. The comprehensive theory of solar cells exists and can be found in textbooks [3][4][5][6] convenient models describing particular aspects of electricity generation in a solar cell, facilitating experimental data interpretation or useful as an enlightening example are still welcome.…”