Perceiving the temperature coefficients of carbon-based perovskite solar cells

Abstract

Perovskite solar cells (PSCs) have emerged in a "catfish effect" of other established photovoltaic technologies with the rapid development of high-power conversion efficiency (PCE) and low-cost fabrication. Among various kinds of PSCs, the organic hole transport layer (HTL) free carbon‐based PSCs (c‐PSCs) has appeared as the most promising devices due to its excellent stability. However, temperature becomes one of the crucial factors in determining the pace of PSCs commercialization. Temperature stress at the interfaces between the perovskite film and the charge transport layers is an essential factor in determining the performance of cPSCs. This work assesses the correlation between the temperature coefficients (TC) and different photovoltaic parameters for HTL free c-PSCs. To evaluate different photovoltaic parameters of the c-PSC as a function of temperature, two different testing approaches such as steady temperature (ST) and transient temperature (TT) conditions have been considered across a wide range of temperature window (5-75 oC) under 1 SUN 1.5 AM. Here the TT testing stands for a single c-PSC undergoing a continuous temperature treatment whereas; the ST testing indicates specific temperature treatment for an individual c-PSC. The maximum efficiency achieved at 25 oC for TT testing devices is ~14.5%, which is ~11% higher than the ST testing devices (PCE ~13%). Moreover, the efficiency temperature coefficient (ETC) for ST testing was found 3.5 x 10-2 (5 °C ≤ T ≤ 25 °C) and -2.1 x 10-2 (25 °C ≤ T ≤ 75 °C), whereas the ETC values of TT testing devices were +2.5 x 10-2 (5 °C ≤ T ≤ 25 °C) and -1.8 x 10-2 (25 °C ≤ T ≤ 75 °C), respectively. The outcome of the temperature stress transmitting through different interfacial layers was further investigated by the thermal imaging for TT devices. On the other hand, X-ray diffraction and scanning electron microscope structural analysis were demonstrated to understand the thermal stress on the overall performance of ST devices. It has been observed that the TC values resulting from TT testing condition are reversible, whereas in the case of ST testing shows irreversible nature and facilitates degradation of the device.