Capacitance of amorphous silicon pin solar cells

Abstract

The i-region of pin solar cells on the basis of amorphous silicon provides the carrier collection. The density of (localized) states (DOS) in this region diminishes the electric field, favors recombination and limits the collection efficiency. The low-frequency capacitance of pin diodes is indicative for the DOS. The small-signal capacitance of a pin solar cell is measured in the frequency range 0.1 to lo3 H z for temperatures between 30 and 100 "C at zero dc bias. A simple diode model is suggested.It involves the assumption of constant DOS values in the p-, i-, and n-regions. These values are determined by fitting. It is shown that low-level doping of the i-region and illumination stress significantly raise the capacitance and the DOS. Das i-Gebiet von pin-Sonnenzellen aus amorphem Silizium besorgt die Sammlung der Ladungstrager. Die Dichte der (lokalisierten) Zustande (DOS) in diesem Gebiet vermindert das elektrische Feld, begiinstigt Rekombination und begrenzt den Sammelwirkungsgrad. Die Niederfrequenz-Kapazitat von pin-Dioden zeigt die DOS an. Die Kleinsignal-Kapazitiit einer pin-Sonnenzelle wird im Frequenzbereich 0,l bis los Hz fur Temperaturen zwischcn 30 und 100 "C ohne uberlagerte Gleichspannung gemessen. Ein einfnches Diodenmodell wird vorgeschlagen. Es beruht auf der Annahme konstanter DOS-Werte in den p-, i-und n-Gebieten. Diese Werte werden durch Anpassung bestimmt. Es wird gezeigt, daB schwache Dotierung des i-Gebiets und Dauerbeleuchtung Kapazitat und DOS deutlich erhohen.

The investigation of an annealing effect on the density of states in a-Si:H film

“…The differential equation ( 1) is solved under the following assumptions: (i) p/i-and i/njunctions are abrupt; (ii) N represents the deep traps and N p , N n denote the shallow traps and they are all constants (Wronski 1979); (iii) the contribution to the space-charge density ρ of the mobile holes and electrons in the extended states is neglected. The junction capacitance in terms of frequency is expressed by means of (Pfleiderer and Rauscher 1983)…”

“…Here we aim to investigate the effect of reverse bias thermal annealing on the DOS of the i-and nregion by means of Pfleiderer's model (Pfleiderer and Rauscher 1983). In order to achieve this goal, p/i/n structures of SnO 2 /a-SiC:H(p + -type)/a-Si:H(intrinsic)/a-Si:H(n + -type)/Al were fabricated.…”

Forward bias capacitance spectroscopy for characterization of semiconductor junctions: Application to a-Si:H p-i-n diode

“…This is the main reason why the characterization of the individual layers of a semiconductor junction prior to its fabrication does not always meet the expected performance in the corresponding device. 31 So far, there have been few reports on the capacitance measurements of a-Si:H p-i-n diodes [32][33][34][35][36][37][38] and except for the attempts to determine DOS at single bias voltages, 32-34 none of them were focused on admittance spectroscopy for the whole DOS distribution. The common results are that the reverse bias capacitance-voltage (C-V) curves at all frequencies simply give out the geometric capacitance of the metal electrodes separated by a material of some dielectric constant.…”

The investigation of the annealing effect on hydrogenated amorphous silicon pin diodes by capacitance techniques

“…In order to achieve this goal, SnO 2 /a-SiC:H(p + -type)/a-Si:H(intrinsic)/a-Si:H(n +type)/Al pin structures were fabricated. In these structures the MGDOS under different annealing conditions in the temperature range 23-175 • C with reverse bias applied was found by means of the differential capacitance-voltage [9], drive-level capacitance [10] and capacitance-frequency [11] methods.…”