您需要为参数（p0）提供合适的初始猜测值。
下面的代码和图像拟合模型：

import numpy as np
from matplotlib import pyplot as plt
from scipy.optimize import curve_fit

time = [0, 30, 45, 60, 75, 90, 300, 600]
des2 = [19.042, 19.019, 19.018, 19.012, 19.011, 19.009, 18.990, 18.984]

def first_order(t, A, tau, A0):
    t0 = t[0]
    y = - (A * (1 - np.exp(-(t - t0) / tau)) + A0)
    return y

parameters, _ = curve_fit(first_order, time, des2, p0=(1, 100, 1))
plt.plot(time, des2)
plt.plot(
    np.linspace(time[0], time[-1], 100),
    first_order(np.linspace(time[0], time[-1], 100), *parameters),
    "--",
)
plt.show()