Optoelectronic transport properties in amorphous/crystalline silicon solar cell heterojunctions measured by frequency-domain photocarrier radiometry: Multi-parameter measurement reliability and precision studies

Abstract

A theoretical one-dimensional two-layer linear photocarrier radiometry (PCR) model including the presence of effective interface carrier traps was used to evaluate the transport parameters of p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) passivated by an intrinsic hydrogenated amorphous silicon (i-layer) nanolayer. Several crystalline Si heterojunction structures were examined to investigate the influence of the i-layer thickness and the doping concentration of the a-Si:H layer. The experimental data of a series of heterojunction structures with intrinsic thin layers were fitted to PCR theory to gain insight into the transport properties of these devices. The quantitative multi-parameter results were studied with regard to measurement reliability (uniqueness) and precision using two independent computational best-fit programs. The considerable influence on the transport properties of the entire structure of two key parameters that can limit the performance of amorphous thin film solar cells, namely, the doping concentration of the a-Si:H layer and the i-layer thickness was demonstrated. It was shown that PCR can be applied to the non-destructive characterization of a-Si:H/c-Si heterojunction solar cells yielding reliable measurements of the key parameters.

Imbalanced charge carrier mobility and Schottky junction induced anomalous current-voltage characteristics of excitonic PbS colloidal quantum dot solar cells

“…4, two independent best-fitting computation programs were used to investigate the reliability and thus the uniqueness of the best-fitted results in a statistical analysis. These programs have been used successfully in earlier multi-parameter fits to experimental data from an amorphous/crystalline silicon solar cell heterojunction [46]. The 'mean-value best fit' minimizes the mean square variance between the experimental data and the theoretical values.…”

An optoelectronic notch (‘dip’) phenomenon in the heterodyne photocarrier radiometry frequency response of Si wafers: a route to quantitative trap-state dynamic processes in semiconductors

“…Here, j and k indicate response harmonics for excitation at angular modulation frequencies ω 1 = 2πf 1 and ω 2 = 2 πf 2 , respectively. Equations (5) show that there are fundamental CDW response frequency components O(1), O(|∆ω| = |ω 1 − ω 2 |) and O(ω 1 + ω 2 ) generated by nonlinear frequency mixing. According to the foregoing discussion, the two-trap densities are taken as time-variable under heterodyne detection through their dependence on the modulated components which are proportional to the optical generation rate G:…”

“…PCR filters out thermal infrared photon emissions and employs a single-element nearinfrared (NIR) sensor to detect photoexcited free-carrierdensity-wave (CDW) radiative recombinations in electronic solids such as silicon wafers by recording the amplitude and phase of PL photon-generated PCR signals. PCR has been used for non-contact simultaneous determination of electronic CDW transport parameters in silicon substrates [2][3][4] and devices [5][6][7] through best-fitting the amplitude-and phasefrequency responses to appropriate CDW theoretical models [8] by means of suitable multi-parameter fitting procedures. Conventional PCR in which the exciting optical beam is modulated at a single frequency is referred to as 'homodyne' (HoPCR).…”

Quantitative Imaging of Defect Distributions in CdZnTe Wafers Using Combined Deep-Level Photothermal Spectroscopy, Photocarrier Radiometry, and Lock-In Carrierography

“…Rapidly growing applications of CdZnTe as a material suitable for X-ray and γ-ray detector fabrication − and for high-efficiency solar cells , have introduced the urgent need for characterization of photocarrier properties and their associated solid-state transport parameters, including their spatial distributions in wafer substrates, which affect charge transport and limit the performance of optoelectronic devices. Most popular diagnostic methods in use are current deep-level transient spectroscopy (I-DLTS), transient current technique (TCT), current and capacitance vs voltage ( I – V and C – V ) measurements, γ-ray spectroscopy, Hall measurements, and optical and thermal measurements. − Beyond those methodologies, photocarrier radiometry (PCR) is a nondestructive and noncontacting spectrally gated frequency-domain dynamic semiconductor photoluminescence (PL) diagnostic modality, which allows for the simultaneous nondestructive determination of electronic transport parameters in semiconductor substrates and devices. − Subsequently, lock-in carrierography (LIC) was introduced as a near-infrared (NIR) imaging extension of PCR, aimed at constructing quantitative images of carrier transport parameters. − Next, two-beam heterodyne LIC (HeLIC) was introduced to address the need for high-frequency photocarrier excitation, eliciting fast enough signal responses required to measure short recombination lifetimes and other fast photocarrier relaxation processes. HeLIC was developed to allow high-frequency dynamic imaging of optoelectronic material and device properties, which require sampling rates orders of magnitude higher than those achievable by the frame rates of today’s fastest NIR camera technologies. − Very recently, heterodyne PCR (HePCR) proved to be very sensitive to photocarrier emission/capture processes out of, and into, band-gap defect and impurity states: a newly discovered HePCR phenomenon giving rise to a frequency-domain heterodyne signal amplitude depression (“dip” or “notch”) accompanied by a 180° phase transition was attributed to a nonlinear kinetic mechanism of laser-excited harmonic carrier density waves (CDW) interacting with trap or defect states in Si wafers .…”