Advanced Detailed Balance Model for Examining Open-circuit Voltage and Short-circuit Current of Perovskite Solar Cells

Professor Choy, Wallace Chik Ho   (Principal Investigator (PI))

Professor Chew Weng Cho   (Co-Investigator)

Dr Jen Alex K.Y.   (Co-Investigator)

42

2017-01-01

675647

Advanced Detailed Balance Model for Examining Open-circuit Voltage and Short-circuit Current of Perovskite Solar Cells

detailed balance model, light trapping, organic/ inorganic solar cells, Perovskite solar cells, photon recycling

Photonics

Engineering (E)

17211916

General Research Fund (GRF)

2016

Completed

1) Establishing advanced detailed balance model to unveil PVSC device physics. We will establish an advanced detailed balance model, which is different from other conventional models (see ""Work done by others""), to simultaneously capture (i) photon recycling effect, (ii) radiative and nonradiative recombination, and (iii) CTL and defect influences in PVSCs. In the advanced model, (i) the photon recycling governed dark current (see ""Research Plan and Methodology"") is computed with the black-body radiation spectrum of PVSCs at their operation temperatures; (ii) the nonradiative recombination due to the traps/impurities will be modeled. The radiative recombination current is calculated from the dark current by Maxwell-Boltzmann statistics; (iii) CTL affected carrier transport and defect influenced current leakage are captured by series and shunt resistances, respectively. Meanwhile, in the model, only three parameters, i.e. nonradiative recombination coefficient, series resistance, and shunt resistance, will be retrieved based on the measured device performances. We will thus fabricate PVSCs with representative device configurations (e.g. CTLs, perovskite materials, and perovskite thicknesses) and measure J-V characteristics and the refractive index of corresponding perovskites at various temperatures. The validation of the model and evolutions of these three retrieval parameters will be demonstrated through studying the experimental results of new PVSCs with different device configurations. Consequently, the advanced model can predict the device performances of PVSCs using only these three retrieval parameters, and has the capability to fully comprehend the above mentioned multi-physics effects in PVSCs; 2) Examining Voc of PVSCs with the consideration of photon recycling effect. While the photon recycling effect and the approach to manipulate the effect for enhancing Voc are inconclusive in PVSCs, we will re-examine Voc by taking into account the effect. When one electron-hole pair recombines to generate a photon in radiative recombination, the photon will be reabsorbed at a different location in SC to create a new electron-hole pair (i.e. photon recycling). The photon recycling effect from the detailed balance between emission and absorption process will enhance Voc. Based on Maxwell-Boltzmann statistics, we will compute the (photon recycling governed) dark current and radiative current of PVSCs with different perovskites using our model. We will compare the amplitudes of radiative current to those of nonradiative current for understanding nonradiative recombination effects on Voc. With the understanding, we will carefully select perovskites to experimentally demonstrate the photon recycling effect and boost Voc with angular-restriction designs. Particularly, a wavelength-dependent angular restriction will be proposed to enhance Voc and suppress dark current without reducing the photocurrent. Since the dark current strongly depends on PVSC operation temperature, the temperature dependence will be examined. Consequently, through the study, the approach included photon recycling effect for manipulating Voc and dark current for high-performance PVSCs will be established; 3) Examining Jsc of PVSCs with architectures tailored for light trapping structures. Jsc has been studied intensively, particularly in various light trapping designs. We will re-examine Jsc via configuring device architectures to match light trapping structures. According to detailed balance model, Jsc can be enhanced by changing absorptivity of cells spectrally with different light trapping designs. However, the improved Jsc will not always lead to enhanced efficiency due to the undesired dark current, increased nonradiative recombination, and unmatched CTLs. We are proposing an approach to design PVSCs with the consideration of different device-configuration parameters for matching a light trapping design by using our advanced model. As a proof of concept, we will use this approach to design PVSCs with a new class of quasi-periodic light trapping structure which is a macroscopically periodic and microscopically random nanostructure, and will fabricate the theoretically optimized PVSCs to demonstrate its effectiveness. Consequently, the proposed approach will allow us to optimize PVSC configurations with a light trapping structure through maximizing not only Jsc but also PCE. *** To show our capability to manage the project, we have started to work on the project. The preliminary results show that, compared to the conventional detailed balance model, our advanced model can better capture PVSC J-V characteristics and provide good prediction capability (see ""Research Plan and Methodology"" for details).